Home

VERY LARGE TELESCOPE NaCo User Manual

1. 6 14 Recommended magnitude ranges for Standard Stars The recommended magnitude range for standard stars in imaging and spectroscopy is given in Table 6 3 Saturation with the minimum DIT can occur for targets that are about 1 magnitude brighter than the lower limit in these ranges but this limit is very sensitive to the level of correction These magnitude ranges are valid for observations with the visual dichroic Limits are similar for the JHK and K dichroics and respectively 0 2 and 3 magnitudes brighter for the N20C80 and N90C10 dichroics For detailed estimates users should use the ETC Table 6 3 Recommended magnitude range of standard stars for observations with the visual dichroic Mode Magnitude Range SW broad band filters 10 12 SW NB filters 8 10 FP 4 6 LW Lp band 7 9 LW Mp band 6 8 LW NB filters 4 6 SW spectroscopy 6 9 LW spectroscopy 4 5 6 6 15 Maximum brightness of observable targets Bright targets leave residual images that can take several minutes to disappear Table 6 4 presents the absolute limits acceptable Table 6 4 Magnitude limits for DIT lt 1 sec IR Magnitude Filters to use gt 6 Any gt 4 and lt 6 Any narrow band filter gt 2 and lt 4 Any filter plus one neutral density filter gt 0 and lt 2 Any narrow band filter plus one neutral density filters Please note that the maximum brightness limit is se
2. Window size Min DIT Max NDIT Temporal noise Spatial Noise ADU ADU 1024 x1026 0 345 127 3 8 TBD 512 x514 0 1091 508 3 9 TBD 256 x258 0 0389 2032 3 9 TBD 128 x130 0 0158 8065 4 3 TBD 64 x 66 0 0072 31775 4 2 TBD Note that windowing introduces higher noise and in some cases some 8 pixel fixed pattern noise Some preliminary results are also listed in Table 5 12 Temporal noise refers to the noise measured on single pixels across the cube Spatial noise refers to noise measured in each single plane stil TBD Cube mode overheads for DCR HD are minimal given the fact that no readout is performed till the entire cube has been produced When using min DIT and small windows overheads increase but are still of the order of few seconds This will likely not be the case for Fowler read More information will be available at the start of the observing period 82 in the NaCo web pages 5 9 Pupil Tracking mode Pupil tracking mode for imaging applications includes 4QPM coronagraphy and SDI Tentatively offered pending commissioning Pupil tracking mode is being implemented to support SAM but given the demand from the community it will be tentatively offered for use with imaging and 4QPM coronagraphic observations In this mode the telescope independently from NaCo tracks the pupil instead of the field This new tracking mode opens the possibility to do Angular Differential Imaging ADI a high contrast imaging te
3. mpn m Sy Position Angle 45 deg Conica FOV 28 for 827 1 1 X Figure 7 3 An illustration of the NACO img obs Autolitter In this example the jitter box width is set to 10 NEXPO is 1 number of offset position is 7 Return to Origin is T and the camera is 27 The dotted line defines the jitter box width The value of the Jitter Box Width parameter corresponds to the full width of the box in which the offsets are generated Defining too wide a box may lead to poor image overlap Conversely too small a value may lead to poor sky subtraction near extended objects By construction there is no telescope offset before the first exposure If the parameter Return to Origin T F is set to true T the telescope moves back to its original position at the end of the template If not the telescope is not moved The total integration time excluding overheads is defined in seconds by DIT x NDIT x NEXPO per offset position X Number of offset positions Table 7 9 describes the parameters of this template Table 7 9 Parameters of NACO_img_obs_AutoJitter P2PP Label Default Values Description DIT NODEFAULT Detector Integration Time sec NDIT NODEFAULT Number of DIT s Readout mode Double_RdRstRd Readout mode Window Size 1024 Size of the window Observation Category SCIENCE Observation Category Store Data Cube T F F Data cube flag Jitter Box width NODEFAULT Jitter box width NEXPO per offset position 1 Num
4. 5 1 4 Pipeline for imaging The NACO img obs AutoJitter and the NACO img obs FixedSkyOffset templates are supported by the pipeline The NACO img obs GenericOffset is only partly supported Sequences of observations with offsets larger than the field of view mosaicking are not reduced by the pipeline The pipeline also calculates zero points and Strehl ratios for data taken with the NACO img cal StandardStar template read out noise from detector darks and it creates master twilight flats master lamp flats and master dark frames 5 1 5 Fabry Perot Imager In P82 Fabry Perot imaging is not offered 5 1 6 Simultaneous Differential Imaging SDI The SDI mode of CONICA obtains four images through three narrow band filters simultaneously Two images are taken outside the 1 6um methane feature at 1 575 um and 1 600 um and two images are taken inside the feature both at 1 625 um All filters have a FWHM of 25 nm The plate scale of the SDI camera is 17 32 mas pixel As of P82 SDI has permanently replaced the old SDI 28 NaCo User s Manual VLT MAN ESO 14200 2761 In SDI the beam splitting is done by means of a double calcite Wollaston with the four images placed on a square The field of view is 8X8 see Figure 5 2 Note that the vertical misalignment of the mask varies with time and cannot be corrected for The SDI has been designed to detect methane rich objects near very bright stars To give an approximate id
5. Information on the CONICA s broadband filters can be found in Table 5 2 and for narrow and intermediate band filters in Table 5 3 Table 5 2 CONICA Broad Band Imaging filters Name Ac FWHM Max Transmission um um J 1 27 0 25 78 H 1 66 0 33 77 Ks 2 18 0 35 70 Lp 3 80 0 62 95 Mp 4 78 0 59 91 26 NaCo User s Manual VLT MAN ESO 14200 2761 Table 5 3 List of narrow and intermediate band filters a oer um um o em Additionally there are two neutral density filters ND Long which can only be used with LW filters and ND Shott which can only be used with SW filters These filters are mounted in another wheel so they can be used in parallel with other filters to reduce the flux of extremely bright 27 NaCo User s Manual VLT MAN ESO 14200 2761 sources The intensity of sources are reduced by factors of 80 and 50 for the ND Short and ND Long filters respectively 5 1 3 Calibration Plan for imaging and SDI For imaging observations a variety of calibration frames will be taken archived and updated at regular intervals The details are describe in the NaCo Calibration Plan http www eso org instruments naos index html Documentation o Nightly zero points provided it is clear in J H and Ks with the 27 objective and visual dichroic Zero points in Lp and Mp with the L27 objective and zero points in the J H and Ks filters with either the 13 or 54 o
6. DEC E Offset x lt Object Positions RA Offset Sky Positions Figure 7 10 An illustration of how the NACO coro obs Stare template works The dashed line connecting position 10 with 1 is the offset done at the end of the template since Return to Origin T F is set to T The rather erratic bold lines are wires which hold the coronagraphic mask in place The AO loop is off when the sky is observed large filled in circles and on when the object is observed small filled in circles In this example the parameter settings were Number of AB cycles 2 Number of Exposures Object Only 2 Number of offset positions Sky only 3 Jitter Box Width 9 Sky offset in Dec 15 Sky offset in RA 35 Return to Origin I F T Camera S13 Table 7 22 Parameters of NACO_coro_obs_Stare P2PP Label Default Values Description DIT NODEFAULT Detector Integration Time sec Readout mode Double_RdRstRd Readout mode Window Size 1024 Size of the window Store Data Cube T F F Store in data cube flag Jitter Box Width NODEFAULT Jitter box width SKY only Number of AB cycles NODEFAULT Number of AB cycles e g 2 for ABAB NDIT for OBJECT NODEFAULT Number of DITs for OBJECT positions NDIT for SKY positions NODEFAULT Number of DITs for SKY Number of exposures NODEFAULT Number of exposures on target Object only Number of offset positions NODEFAULT Number of exposures on sky Sky only Sky offset in RA NODEFAULT RA offset f
7. For very bright target a neutral density filter can be inserted into the light path The choices are Full for no neutral density filter ND Long for a LW neutral density filter and ND_Short for a SW neutral density filter Since the J band filter is in the same wheel as the Wollaston J band polarimetric observations are not feasible 7 7 1 NACO_pol_obs_GenericOffset This template is used for imaging polarimetry It can be used with all filters with the exception of J and Mp Rotator offset angles can now be entered as a list The angles are relative so a sequence with 0 45 45 45 would rotate the field by 0 45 90 and 135 degrees from the original rotator position Due to difficulties in compensating for rotator offsets with the FS we are presently requesting observers to keep the relative offset angle to 45 degrees or less Additionally the user can choose to rotate the rotator to the original rotator position once the template has ended with the parameter Return to the Original Rotator Position T F For observations with NAOS CONICA the default value for this flag is False 98 NaCo User s Manual VLT MAN ESO 14200 2761 After each rotator offset the telescope can offset according to a user defined list Spatial offsets are defined with the parameters List of offsets in X and List of offsets in Y The offsets are relative to the previous position are in X and Y and are defined in arcsec Additionally the observation type can
8. NaCo User s Manual VLT MAN ESO 14200 2761 Figure 9 2 Illustration of the extinction curve used when giving a non zero value to the extinction Ay The J H K and R bands are shown for reference along with the monochromatic wavelength for V The bottom graph represents the quantum efficiency for the WFS detectors as a function of wavelength 9 5 5 Optimizing NAOS and Getting a Performance Estimation The optimal configuration i e the one giving the highest Strehl and the resulting PSF are determined when the Optimize button located in the bottom left corner of the graphical user interface is selected The typical response time from the server is 10 seconds and should not exceed 60 seconds When more than one reference object has been defined the optimization is done for the selected highlighted one For complete preparation the Optimize command should be repeated for each potentially viable reference object Once you have made a request for optimization and if it has been successfully processed the GUI will be updated with the optimal AO configuration Figure 9 4 and an estimation of the resulting PSF The Strehl ratio is always computed for the reference object on axis at the 116 NaCo User s Manual VLT MAN ESO 14200 2761 observing wavelength and at 2 166 um For the science target off axis the Strehl ratio is given at the observing wavelength only Tracking Table Data 8 DEG G 10 0
9. A further data cleaning strategy is based on frame selection over this data cube any frames with poor AO performance or any other strange effects are rejected This can be easily achieved by cutting the data according to outliers in simple statistical tests on quantities such as the counts in the peak pixel the total counts etc 5 6 7 PSF calibrations strategies As with all forms of optical interferometry it is paramount to preserve a focus on calibration To do this it is suggested to bracket observations of the science target with observations of a nearby point source reference object Ideally this reference star will be an unresolved point or if not at least a single star of well known size Good calibration is helped by observing the reference star s at similar airmass and observed with as near identical telescope AO configuration as possible Finding reference stars is straightforward but does take some work and it may help to consult some local interferometrists or interferometry web resources some institutions such as the Michelson Science Center have calibrator finding catalogue search engines available online For the case of CONICA the resolutions are relatively modest so almost all single stars of any spectral type will present photospheres that are essentially unresolved with the exception only of a handful of extremely bright red late M supergiants and Miras This being the case a good calibrator is then any star which i
10. NACO spec cal NightCalib TT NaCo User s Manual VLT MAN ESO 14200 2761 With the exception of standards the minimum amount of time between exposures is 30 seconds This limit is set to allow the telescope Active Optics to at least perform one correction Ensure that the correct filters are used when acquiring bright targets for spectroscopy When doing a blind offset from a bright reference object to a faint target we strongly recommend that the position angle be set so that the reference object and target fall in the slit at the same time Additionally the coordinates of the reference object are the ones that should go into the OB When using extended objects as AO reference sources make sure that the flux within the specified aperture is correct Users tend to significantly overestimate this flux The verify button on P2PP checks that individual parameters are within the defined ranges and some additional checking on the global logic of selected OBs The Strehl seeing and airmass constraints as well as the epoch equinox and RA and DEC and respective proper motion fields of P2PP will be automatically filled when the configuration file is loaded Do not edit these fields There must be one AO configuration file per target The same AO configuration file cannot be used for different targets 7 1 1 Offset conventions and definitions Position Angle 0 deg Position Angle 45 deg 1024 1024 1024 1024 Coni
11. SW coronagraphy of a bright source with Double_RdRstRd 74 Table 6 13 Example 7 LW coronagraphy of a bright source 74 Table 6 14 Example 8 Imaging with chopping 75 Table 6 16 Example 10 A bright source with SDI 75 Table 7 1 NaCo template suite 77 Table 7 2 Parameters of NACO img acg MoveToPixel 81 Table 7 3 Parameters of NACO img acqg SDIMoveToPixel 82 Table 7 4 parameters of NACO img acg MoveToS lit 83 Table 7 5 Parameters of NACO_img_acq_MoveToMask 84 Table 7 6 Parameters of NACO img acqg SDIMoveToMask 85 Table 7 7 Parameters of NACO img acg Polarimetry 85 Table 7 8 Parameters of NACO_img_acq_S AMMoveToPixel 86 Table 7 9 Parameters of NACO img obs Antofitter 87 Table 7 10 Parameters of NACO img obs GenericOffset 88 Table 7 11 parameters for the example shown in Figure 7 4 89 Table 7 12 parameters for the example shown in Figure 7 5 89 NaCo User s Manual VLT MAN ESO 14200 2761 Table 7 13 parameters of NACO_img_obs_AutoChopNod Table 7 14 Parameter of NACO img obs FixedSkyOffset Table 7 15 Parameters of NACO img cal StandardStar Table 7 16 Parameters of NACO_sdi_obs_GenericOffset Table 7 17 Parameters of NACO_spec_obs_AutoNodOnSlit Table 7 18 Parameters of NACO_spec_obs_GenericO fet Table 7 19 Parameters of NACO_spec_cal_NightCalib Table 7 20 Parameters of NACO pol obs GenericOffset Table 7 21 Parameters of NACO pol obs Retarder Table 7 22 Parameterf of NACO como obs Stare Table 7 23 P
12. s Manual VLT MAN ESO 14200 2761 Uncorr Template parameters Acquisition Template NACO img acq MoveToPixel Observation Template NACO img obs Autolitter DIT 0 2 sec NDIT 150 Number of offset positions 120 NEXPO per offset position 1 Readout Mode Uncotr Execution Time min Preset 3 Guide Star Acquisition 0 75 Initial Setup 2 AO Acquisition 5 Imaging acquisition 0 5 Sub Total acquisition 11 25 Observation 120x 27 150x0 2 114 Total min 125 Overheads 108 Observation Number of offset positionsx Offset overhead DITxNDIT Table 6 9 Example 4 Spectroscopy of faint source with FowlerNsamp Template parameters Acquisition Template NACO_img_acq_MoveToSlit Observation Template NACO spec obs AutoNodOnSlit DIT 300 sec NDIT 1 Number of AB or BA cycles 6 NEXPO pet offset position 1 Readout Mode FowlerNsamp Return to Origin T Jitter Box Width 10 Execution Time min Preset 3 Guide Star Acquisition 0 75 Initial Setup 2 AO Acquisition 10 Spectroscopic acquisition 5 Through slit 2 Sub Total acquisition 22 75 Observation 2x6x 27 300 2 65 8 Total min 88 6 Overheads 48 Observation 2xNumber of AB or BA cyclesx Offset overhead DIT readout overhead Table 6 8 Example 3 Imaging a bright source in the L band V 11 for the VIS WE
13. 1 4 1 4 C 0 7 sep 10 0 7 a apateni 3 5 X 10 transmissivity situated on a glass plate 4QPM_K 0 15 Four quadrant phase mask for K band 13x13 FOV The diameter is that of the central Lyot spot 4QPM_H 0 15 Four paiar phase mask for H band 8x8 FOV The diameter is that of the central Lyot spot 5 2 1 Performance of the semitransparent mask C 0 7 sep 10 The contrast between inside and outside of the 0 7 semi transparent mask has been measured to be AKs 6 3 0 1 mags and AH 6 0 0 1 mags The opaque masks are held by wires and the semi transparent mask is situated on a transparent plate 5 2 2 Performance of the 4QPMs The two four quadrant phase masks 4QPM reduce the intensity of a source by adding a phase shift of x to the wavefront Unlike the classical Lyot masks a phase mask coronagraph splits the focal plane into four equal areas two of which are phase shifted by m As a consequence a destructive interference occurs in the relayed pupil and the on axis starlight rejected outside the geometric pupil is filtered with a diaphragm a Lyot stop of 0 15 diameter The advantage over a classical Lyot mask is twofold there is no large opaque area at the centre enabling observations of objects that are within 0 35 of the main source and a larger achievable contrast is met cfr Boccaletti et al The four quadrant phase mask coronagraph PASP 116 p 1061 2004 There are two such masks available Fi
14. 1 degree in declination and a few minutes in right ascension In these conditions an improvement of a factor 10 can be expected on the averaged contrast A contrast of 9 to 9 5 mag is achievable at 0 5 separation in H and Ks Other techniques involving field rotation active or passive can be envisaged but are not tested yet Given the above the use of the four quadrant phase mask is restricted to Visitor Mode observations 35 NaCo User s Manual VLT MAN ESO 14200 2761 5 2 8 Calibration plan for coronagraphy For coronagraphic observations a variety of calibration frames will be taken archived and updated at regular intervals The calibrations are described in detail in the NaCo Calibration Plan o Twilight flats and daytime lamp flats as described in 5 1 3 These calibrations are done without the focal plane masks o Detector darks in all readout modes and DITs 5 2 9 Night flat fields for coronagraphy Imperfections on the plates that hold the semi transparent Lyot mask and the 4QPMs together with instrument flexure means that flat fields depend on the rotator angle The template NACO_coro_cal_NightCalib allows one to take nighttime flat fields immediately after coronagtaphic data have been taken We strongly recommend that these calibrations be taken for the said masks Nighttime flat fields with the fully opaque masks are not needed These flats are taken without the mask Given the low transmissivity of the semi transparen
15. 10 0 12 0 12 0 13 0 13 0 15 0 5 0 12 0 12 0 13 0 13 0 Figure 9 3 An example of tracking table window acquisition and observation of moving objects Offsets in RA and DEC ate given in arcsec Figure 9 4 Performance subpanel the AO optimal configuration and the PSF is available from buttons in this panel 117 NaCo User s Manual VLT MAN ESO 14200 2761 The optimal Adaptive Optics configuration can be displayed by clicking on the AO Config button in the subpanel depicted in Figure 33 An example is shown in Figure 9 5 AO Configuration VIS Figure 9 5 Pop up window showing an optimal configuration of the AO system You do not have to worry about these parameters but they may give you some insight into the way NAOS works From the perspective of the astronomer the most significant result of the optimization is the corresponding estimated performance in terms of image quality It is expressed quantitatively by the computed point spread function PSF and its derived quantities The PSF is returned to the user interface in FITS format It characterizes the quality of the optical beam which is provided by NAOS to CONICA and is thus logically computed at the observing wavelength and is available from the Resulting Performance area of the GUI The provided PSF is computed off axis i e in the direction of the target seen by CONICA The PS computes these data on 128x128 pixels One pixel corresponds
16. 33 would result in images that are taken 0 33 33 and 0 degrees from the original rotator position Due to difficulties in compensating for rotator offsets with the FS we are presently requesting observers to keep the relative offset angle to 45 degrees or less Additionally the user can choose to rotate the rotator to the original rotator position once the template has ended with the parameter Return to the Original Rotator Position T F For observations with NAOS CONICA the default value for this flag is False The total number of exposures is given by number of rotator positions x Number of offset positions x NEXPO per offset position With this scheme it is possible for the user to sample the object and the sky as desired at several rotator positions It is also possible to code the template so that the object and sky are sampled as 93 NaCo User s Manual VLT MAN ESO 14200 2761 desired for one angle only The template can be restarted with another orientation on the sky for another series of exposures The total integration time excluding overheads is defined in seconds by DIT x NDIT x NEXPO per offset position x Number of offset pos x number of rotator pos Table 7 16 Parameters of NACO_sdi_obs_GenericOffset P2PP Label Default Values Description DIT NODEFAULT Detector Integration Time sec Readout mode Double_RdRstRd Readout mode Window Size 1024 Size of the window Store Data Cube T F F Data cube flag List
17. 4 with the acquisition position is the offset done at the end of the telescope since the Return to Origin I F was set to T In this example the parameter settings were Number of offset positions 4 NEXPO per offset position 1 Observation Type O or S OSSO Offset Coordinates DETECTOR List of offsets in RA or X 70 140 List of offsets in DEC or Y 0 707 Return to Origin T F T Table 7 18 Parameters of NACO sper obs GenericOffset P2PP Label Default Values Description DIT NODEFAULT Detector Integration Time sec NDIT NODEFAULT Number of DITs Readout mode FowlerN samp Readout mode NEXPO per offset position 1 Number of exposures per offset position Number of offset positions NODEFAULT Number of offset positions Observation type O or S NODEFAULT Oisin closed loop S in open loop Offset coordinates NODEFAULT SKY or DETECTOR List of offset in RA or X NODEFAULT Offsets in arcsec List of offset in DEC or Y NODEFAULT Offsets in arcsec Return to Origin T F T Return to Origin Slit NODEFAULT Name of slit Spectroscopic Mode NODEFAULT Spectroscopic Mode 97 NaCo User s Manual VLT MAN ESO 14200 2761 7 6 3 NACO spec cal StandardStar This template is used for spectroscopic standard star observations It is strictly equivalent to the NACO spec obs AutoNodOnSlit template in the definition of the parameters The user is referred to 7 6 1 for the description of the parameters This template should be used by us
18. 4Q ref stand for direct corona graphic imaging respectively not using and using reference subtraction For all the lines that are called SDI we are studying the spectral subtraction image at 1 575um image at A 1 625um SDI and SDI roll show the results of SDI subtraction with and without roll averaging It is the same for SDI ref and SDI ref roll but using also the subtraction of the SDI image of a reference star at the same parallactic angle The SDI double subtraction is described in details in the text For the detection level estimation we supposed that the companion has a contrast of 100 in the methane band no flux in the image at A 1 625um Obviously for a companion located at close angular separation the PSFs may overlap and subtract themselves In our case a simple simulation using the real PSF image has been used to estimate the attenuation of the positive PSF For an angle of 25 the PSF is attenuated by 20 at 150 mas and less than 4 at 300 mas The blue curve showed in Figure 5 12 has been corrected for this effect by dividing the detection level calculated on the double roll subtraction images by the theoretical 39 NaCo User s Manual VLT MAN ESO 14200 2761 attenuation This last technique is outperforming all the others except at very short angular separation less than 0 15 where the SDI subtracted by an SDI reference is better However since it does not use a reference image the exposure time on
19. CALIBRATIONS FLAT FIELDS AND DATA CLEANING PSF CALIBRATIONS STRATEGIES IMAGING TESTS ON SKY OBSERVATIONS VY CANIS MAJORIS 31 31 31 31 32 32 33 34 34 36 36 36 36 37 38 40 40 40 41 42 42 42 43 43 43 44 44 45 45 46 47 47 47 48 49 49 49 50 NaCo User s Manual VLT MAN ESO 14200 2761 5 6 10 FAINT COMPANION DETECTION 5 6 11 ON SKY OBSERVATIONS AB DOR IN H AND K 5 6 12 ON SKY OBSERVATIONS HD39213 INK 5 6 13 PSF AND MTF 5 6 14 5 6 15 REFERENCES AND FURTHER READINGS 5 6 16 CALIBRATION PLAN FOR SAM 5 6 17 PIPELINE FOR SAM 5 7 5 7 1 5 12 5 7 3 5 8 5 9 CONICA DETECTOR GENERAL CHARACTERISTICS DIT AND NDIT READOUT MODES AND DETECTOR MODES CUBE MODE PUPIL TRACKING MODE 6 OBSERVING WITH CONICA AT THE VLT CALCULATING EXPOSURE TIMES THROUGHPUT AND SENSITIVITY FOR SELECTED FILTERS 61 6 1 6 2 6 3 6 4 6 5 6 6 6 6 1 6 6 2 6 6 3 6 6 4 6 6 5 6 6 6 6 7 6 8 6 9 6 10 6 11 6 12 6 13 6 14 6 15 VISITOR MODE VM OPERATIONS ACTIVE OPTICS VERSUS ADAPTIVE OPTICS THE INFLUENCE OF THE MOON TELESCOPE CONTROL CHOPPING AND COUNTER CHOPPING TARGET ACQUISITION IMAGING SPECTROSCOPY CORONAGRAPHY SDI 4 POLARIMETRY SAM PRE IMAGING FINDING CHARTS README FILES AND OB NAMING CONVENTIONS REFERENCE SOURCES FOR WAVEFRONT SENSING MEASUREMENT OF STREHL RATIO AND CLASSIFICATION OF OBS IN SERVICE MODE PSF REFERENCE STAR RECOMMENDED DIT AND NDITS IR BACKGROUND REC
20. CONICA the Preparation Software PS See Appendix B is a key tool since it allows one to optimize the adaptive optics configuration and to estimate performance Both the Exposure Time Calculator ETC and P2PP use the output from PS to determine feasibility and to prepare observations For phase II preparation the PS must be used The ETC can be accessed via the regular web based interface http www eso org observing etc or via the HTML file produced by PS For the former the ETC now calls the NAOS PS server itself to retrieve the performance estimate For phase I preparation users can use either access route although we strongly recommend the use of the PS for phase I preparation as well At the telescope OBs are executed by the instrument operator Both NAOS and CONICA are setup according to the contents of the OB Note that the NAOS configuration might be further optimized at this time in order to provide better performance A Real Time Display is used to view the output of CONICA and to perform acquisitions while the wavefront pupil is also displayed Daytime calibrations are executed the following morning by observatory staff 6 1 Visitor Mode VM operations Visitors arrive on Paranal two days ahead of their observing run and receive support from Paranal Science Operations PSO Users are requested to read the P2PP and NAOS CONICA User Manuals before arriving During the night users do not have direct interaction with t
21. F F Data cube flag NEXPO per offset position 1 Number of exposures per offset position Number of offset positions NODEFAULT Number of offset positions List of offsets in X NODEFAULT Offsets in arcsec List of offsets in Y NODEFAULT Offsets in arcsec Filter NODEFAULT Filter name Neutral Density Filter Full Neutral density filter Full none Camera NODEFAULT Camera Name 92 NaCo User s Manual VLT MAN ESO 14200 2761 7 4 6 NACO img cal ChopStandardStar This template is used for standard star observations that require chopping It is strictly equivalent to the NACO img obs AutoChopNod template in the definition of the parameters 7 4 3 This template should be used by users who need calibrations standard stars beyond the ones provided by the Calibration Plan of this mode The only difference with NACO img obs AutoChopNod is that some DPR keywords in the FITS headers of the images are set to values that allow pipeline processing and archiving 7 5 Simultaneous Differential Imaging SDI template The simultaneous differential imager SDI uses special templates to acquire and observe targets 7 5 1 NACO sdi obs GenericOffset This template is used exclusively with the SDI mode It is similar to the NACO pol obs GenericOffset template in that it allows one to rotate the field of view as well as offset the telescope At each rotator angle the telescope offsets according to a user defined list Offsets are defined with the p
22. NaCo User s Manual VLT MAN ESO 14200 2761 to combine chopping with telescope nodding i e offsetting in the opposite direction of the chop because chopped images usually leave strong residuals on the detector due to the different optical paths through the telescope With AO fed systems there is an added complication The amplitude of the residuals depends on the strength of the turbulence stronger turbulence means that the deformable mirror has to work harder and the residuals on the two sides of the nod are generally different Consequently they cannot be perfectly removed For observations with NaCo it is not necessary to use chopping and nodding for LW imaging spectroscopic and polarimetric observations if the central wavelength of the filter is less than 4 2 um the sky is sampled frequently i e more than once per minute and if conditions are clear But for coronagraphic observations where one cannot jitter and for filters with wavelengths greater than 4 2 um efficient subtraction of the sky background will require chopping and nodding 3 6 Spectroscopy Spectroscopic observations with an AO system lead to the following effects o An increase in the Strehl ratio along the spectrum with increasing wavelengths Depending on the setting the Strehl ratio can change by 10 o A wavelength shift caused by the change in the Strehl ratio as a function of wavelength In particular at shorter wavelengths the FWHM of the PSF of the s
23. a fraction of incoming light at the observing wavelength Resulting Performance PointSpread Function on target 0 032 x axis max 0 0296 FYVHM x 0 094 0 020 l FYVHM Y 0 073 Sr 15 30 0 024 Dismiss 0 016 0 012 0 0080 0 0040 0 95 0 80 0 64 046 032 0 15 0 00 0 16 0 32 048 0 64 0 80 0 96 arcsec Figure 9 6 Pop up window showing the PSF profile This also gives access to the PSF FITS file The different width of the PSF in x and y direction are due to anisoplanatism The x axis is here defined as the axis that is parallel to the line connecting the reference object with the science target 9 5 6 Exporting to the Exposure Time Calculator When clicking on Export to CONICA ETC at the bottom of the main panel a file browser pops up You can then give the name of an HTML file that will be created by the GUI and saved to your local disk This HTML file contains the PSF profile the CONICA filter and the magnitude and spectral type of the target 119 NaCo User s Manual VLT MAN ESO 14200 2761 To call the ETC load this file into your favorite web browser and click on the Call CONICA ETC button at the bottom of the page 9 5 7 Exporting to P2PP All NaCo acquisition templates Section 7 3 require a configuration file which is produced by the Export to P2PP button It has the default extension aocfg and it is saved in the directory specified in the Preferences menu under the option set the
24. adhered to 6 6 3 Coronagraphy It is mandatory to use the NACO_img_acq_MoveToMask acquisition template for all coronagtaphic OBs and the same mask in both the acquisition and observing templates This template provides interactive tools to centre objects behind the selected mask which is overlaid on the RTD 6 6 4 SDI 4 It is mandatory to use the NACO img acq SDIMoveToMask acquisition template for all SDI 4 OBs and also use the same setup in both the acquisition and observing templates with the possible exception of the ND Short filter which is used during acquisition of bright stars This template provides interactive tools to centre objects behind the 4QPM_H mask 6 6 5 Polarimetry It is mandatory to use the NACO img acq Polarimetry acquisition template 6 6 66 SAM It is mandatory to use NACO img acq SAMMoveToPixel 6 7 Pre Imaging Pre imaging is offered for programs where critical conditions need to be checked to guarantee the successful execution of the science program This mode ensures a quick delivery of the data to the user and is restricted to programs that have already requested a separate pre imaging Run or otherwise indicated an amount of time to be used for pre imaging Examples of cases that may require pre imaging are programs needing to check either the field orientation because of possible contamination by a close by bright star or the possible binarity of potential targets for occultations or to refin
25. and polarimetric observations with the other LW filters Lp NB_3 74 and NB_4 05 chopping is optional The basic characteristics and definitions of chopping are O The chopping throw is the distance between the ON and OFF beams The maximum chop throw is 20 Bests results are provided for a chop throw of 15 which is the recommended limit The chopping angle can be defined with reference to the SKY or to the DETECTOR The chopping frequency is automatically defined in the templates and is based on the filter that is being used It typically varies between 0 1 and 0 2 Hz One chop cycle corresponds to one ON OFF cycle i e one period of the M2 chopping motion Several chop cycles can be averaged by the pre processor to deliver one image This is referred to as the Number of chop cycles and this parameter is automatically set by the templates The detector acquisition system delivers the two half cycle frames the ON and OFF images averaged over the number of chop cycles and the subtracted frame ie ON OFF Objects at the ON position appear negative objects at the OFF position if within the field of view appear positive Only the half cycle frames are saved to disk and sent to the archive These frames are stored in a cube The first plane in the cube corresponds to the ON image and the second plane corresponds to the OFF image and so on Chopping is always associated with nodding in the opposite direction of the chop Th
26. and the reference are the same and for a source that is 30 away from the reference star The assumed seeing values are 0 8 and 1 2 at Zenith at a wavelength of 0 5 mm These values were derived with the Preparation Software PS and are also used in the CONICA Phase I Exposure Time Calculator to estimate signal to noise ratios V magnitude Strehl ratios SR On axis 30 off axis On axis 30 off axis 0 8 seeing 0 8 seeing 1 2 seeing 1 2 seeing 10 0 47 9 32 1 5 11 5 44 9 12 1 4 13 0 26 7 7 1 3 14 5 17 5 5 1 0 16 0 5 3 1 0 7 Note that a seeing of 0 8 or better can be obtained on Paranal 50 of the time while 1 2 or better can be obtained 80 of the time 4 3 Anisoplanatism Anisoplanatism is the field dependence of the PSF It corresponds to the angular decorrelation of the wavefront coming from two angularly separated stars This phenomenon affects the quality of the AO correction in the direction of the target when the reference star is not on axis 4 4 Laser Guide Star facility LGSF Adaptive Optics Operations are strongly affected by the size of the isoplanatic angle usually 20 at 2um but only 5 in diameter at 0 6um Even for observations at 2 2um the sky coverage achievable by this technique equal to the probability of finding a suitable reference star in the isoplanatic patch around the chosen target is only of the order of 0 5 to 1 Th
27. be defined for each image and is entered as a list in the parameter Observation Type O or S O stands for Object and assigns the DPR TYPE header keyword to OBJECT S stands for Sky and assigns the DPR TYPE header keyword to SKY The AO loop is closed for the former and open for the latter The total number of spatial offsets is defined by the parameter Number of offset positions This number can be different from the number of elements in the aforementioned lists If the number of spatial offsets is larger than the number of elements in a list the list is restarted from the beginning as many times as needed until the correct number of offsets have been done These lists can have any length however having lists of different lengths can become extremely confusing It is good practice to use lists of equal length or lists with only one value if one parameter is not changed The total number of exposures is given by number of rotator positions x Number of offset pos x NEXPO per offset pos Unlike other templates this template does not have a Return to Origin I F flag This flag refers to the spatial offsets only and the template will do this automatically before rotating the rotator to the new position Table 7 20 describes the parameters of this template With this scheme it is possible for the user to sample the object and the sky as desired at several rotator positions It is also possible to code the template so that the
28. cache folder This file contains all the information relevant to the setup of NAOS during acquisition of the target When preparing your observations with the PS and P2PP the following points should be noted o The output file is a text file and it should never be manually edited If you do the execution of your OB will be seriously compromised o There must be one configuration file per target The same configuration file cannot be used for different targets but is fine for different OBs using the same target o The configuration file is inserted into the NAOS parameter file keyword of the relevant acquisition template o The Strehl seeing and airmass constraints and the RA and DEC fields of P2PP will be automatically filled when the configuration file is loaded Do not edit these fields 9 5 8 Exporting OBs from P2PP The export facility in P2PP allows one to export observing blocks For NaCo two files are produced one with the extension obx and another with the extension aocfg These files should be kept in the same directory P2PP will report an error if the two files are in different directories 9 5 9 Saving Restoring a PS Session The complete PS session can be saved on local disk and restored The Save Session and Load Session functions available from the File menu of the main panel allow you to save or load the corresponding information on your disk Please be aware that loading a previously saved session file will d
29. centred target without the mask and the second image is an image of the target accurately centred behind the mask If four images are recorded then these images become respectively the 3rd and 4th images and the first two are images of the reference and they are used by the operator to classify the OB For the case the 4QPM masks and the semi transparent mask C_0 7_sep_10 the recorded images are o One flat on halogen lamp is on and one flat off image these images can be used for flat fielding the subsequent science frames 83 NaCo User s Manual VLT MAN ESO 14200 2761 o An image of the star off the mask 2 off with the ND filter inserted if specified in the initial setup and an image of the sky these images can be used as PSF calibrator Then the following steps are performed o Rough offset to position the star behind the mask o Removal of the ND_Short filter if used For 4QPM the Full Uszd mask is used All other masks use Full o Adjustment of DIT if needed o Fine centring behind the mask o Record the final acquisition image of the star finely centred behind the mask without the ND filter Table 7 5 Parameters of NACO_img_acq_MoveToMask P2PP Label Default Values Description DIT NODEFAULT Detector Integration Time sec NDIT NODEFAULT Number of DITs Type of AO Observation LGS NGS NODEFAULT LGS or NGS observation type PSF Reference T F F Set to T if it is a PSF reference star Pupil Tracking M
30. finer and it takes longer for exposures to be sky noise limited However if there are bright objects of scientific interest in the field of view then DITs will have to be much smaller than the ones listed in Table 6 1 For DITs larger than 60 seconds users should consider using FowlerNsamp and not Double_RdRstRd With DITs larger than 60 seconds the number of hot pixels in Double_RdRstRd is noticeably larger Table 6 1 Recommended DIT and NDIT range Filter DIT sec DITxNDIT sec J SW NB filters 60 300 120 300 H and Ks 20 120 60 240 LW NB filters 0 175 2 4 40 80 Lp 0 175 30 SW Spectroscopy 60 900 120 900 LW Spectroscopy 0 4 3 0 60 120 These recommendations do not necessarily hold for cube mode where the choice of DIT and NDIT will depend on the application For observations that use chopping DIT and NDIT are computed automatically by the templates 66 NaCo User s Manual VLT MAN ESO 14200 2761 6 13 IR background Background is a function of the filter and the dichroic They are listed in Table 6 2 Users should note that the RON of the array can dominate if DIT is too small Table 6 2 IR Backgrounds The hyphens mark invalid combinations of a NAOS dichroic CONICA filter Filter Background magnitude sq arcsec VIS N20C80 N90C10 JHK K J 15 8 15 8 15 8 5 8 H 14 0 14 0 14 0 14 0 Ks 12 8 12 5 11 0 Lp 3 0 3 0 Mp 05 0 5
31. having the NGS on axis with the LGS It is also important to remember that due to the Cone effect the maximum Strehl achievable with the LGS is significantly less than the one obtained with a bright natural guide star 20 against 40 in K band with the AO reference on axis For information the LGS is expected to have a magnitude equivalent to that of a star in the range my 11 13 In order to apply for the LGS mode just make sure that you have a natural guide star within 40 from your object and that no other mode can be used It should be stated clearly in the proposal why only this mode can be used and which NGS will be used for tip tilt sensing There are borderline cases when one has to decide whether to select LGS or NGS mode The limiting magnitude is currently my 13 5 14 i e with AO reference stars which are fainter than this limit one should select LGS mode and keep the star as a tip tilt reference Brighter stars offer better performance in NGS mode When using the PS a good rule of thumb is the following if the expected Strehl ratio calculated for the NGS mode is 10 or higher stay with NGS Otherwise move to LGS Chopping observations are impossible in LGS mode thus M band observations cannot be performed 69 NaCo User s Manual VLT MAN ESO 14200 2761 Table 6 5 NaCo Overheads Acquisition Templates Description Overhead Comment Telescope Preset 3 min Guide star acqui
32. may be marginally OK with broadband filters such as Ks Lp or Mp Useful range is from about 3 to 7 Mag fainter if bandwidth smearing is not an issue Gives very good Fourier coverage and could be used for mapping relatively simple objects Good for faint companions BB_9Holes This mask was specifically optimized for broadband hence BB_ operation and should be used with the broad filter set Although bandwidth smearing is unavoidable this mask is not affected because the holes are arranged to that they do not smear into each other Useful range of target brightness is about 5 to 10 Fourier coverage is not as good as 9Holes 7Holes This mask passes the most light and should operate from about 8 to 11 or maybe 12 mag Probably it is most useful for faint companion detection due to limited Fourier coverage 48 NaCo User s Manual VLT MAN ESO 14200 2761 5 6 6 Calibrations flat fields and data cleaning Data processing entails all the normal imaging data tasks such as subtraction of any bias flat fielding and removal of bad pixels To obtain flats and bad pixel maps we have found that the standard CONICA procedures and data reduction software were fine Results using the standard flats were compared with flats generated by hand with the finding that there was no significant difference Normally masking data will be taken in a data cube mode which yields a large sample of the interferograms up to several hundred frames
33. motion or tilt determination problem Because the paths of the light rays are the same on the way up as on the way down the centroid of the artificial light spot 22 NaCo User s Manual VLT MAN ESO 14200 2761 appears to be stationary in the sky while the apparent position of an astronomical source suffers lateral motions also known as tip tilt The simplest solution is to supplement the AO system using the LGS with a tip tilt corrector set on a generally faint close NGS V 17 or brighter Performance is then limited by the poor photon statistics for correcting the tip tilt error The need of a natural guide star for tip tilt sensing is the reason why sky coverage cannot go up to 100 for LGS AO The Laser Guide Star Facility LGSF at UT4 is a joint project in which ESO built the laser room beam relay and launch telescope while MPE and MPIA provided the laser itself The PARSEC project is based on a 4W CW Sodium Laser 589 5 nm focused at 90 km altitude in the mesosphere The thin layer of atomic sodium present at that height backscatters the spot image and produces in best conditions a V 11 artificial star to guide the AO servo loop More typically the artificial guide star is in the range V 11 13 This artificial reference star can be created at the position specified by the target coordinates and the NAOS visible wavefront sensor is used to correct the high order wavefront aberrations on the target object The laser is host
34. of 4QPMs Contrasts were measured on the PSF fibre for the 4QPM K and the 4QPM_H Azimuthally averaged radial profiles are shown in Figure 5 7 and provide an averaged contrast 32 NaCo User s Manual VLT MAN ESO 14200 2761 Another metric commonly used is the maximum attenuation which refers to the ratio of the maximum intensity in the PSF image to that of the coronagraphic image Although maximum intensity is at r 0 on the PSF it is located at 1 5 2 A D on the coronagraphic image Radial contrast does not reflect directly this value because of azimuthal averaging The maximum attenuation is about 100 a little bit more in the H band probably because the Lyot spot is larger with respect to A D at shorter wavelengths This is comparable to the result obtained in 2004 with the first 4QPM implemented in NaCo In this case the limit of contrast is set by the residual static aberrations likely originating from non common path aberrations 5 2 5 Chromaticity of 4QPMs Phase shifts as provided by phase masks are chromatic However the chromaticity effect must be balanced with other sources of degradations Chromaticity turns out not to be an issue for NaCo Even with the fibre source we observed very small variations as a function of the filter bandwidth as shown in Figure 5 8 The attenuation reaches a factor 60 70 in both Ks and NB_2 17 filters Under atmospheric seeing the effect of chromaticity is totally negligible and a 4QPM designed for
35. of NDITs NODEFAULT List of NDITs NEXPO per offset position 1 Number of exposures per offset position Number of offset positions NODEFAULT Number of offset positions Observation type O or S NODEFAULT O is in closed loop S in open loop List of offsets in X NODEFAULT Offsets in arcsec List of offsets in Y NODEFAULT Offsets in arcsec Return to the Original F Rotator position at the end of the template Rotator position T F List of position angle offsets NODEFAULT List of rotator offsets in degrees Neuttal Density Filter Full Neutral density filter Full none 7 6 NaCo spectroscopic science templates For SW observations the readout mode of the detector can be set to either FowlerNsamp or Double_RdRstRd for LW observations the readout mode will be set to Double_RdRstRd The width of the slitless mask is 13 arc seconds which is half the length of the regular slits Users should keep this point in mind when programming the offsets For the NACO spec obs AutoNodOnSlit and NACO_spec_cal_StandardStar templates this means that the nod throw should be less than 10 7 6 1 NACO spec obs AutoNodOn amp Slit This template nods the telescope between two positions A and B along the slit A cycle is a pair of AB or BA observations Cycles are repeated on ABBA sequences E g 3 cycles correspond to an ABBAAB sequence 4 cycles correspond to an ABBAABBA sequence etc Table 7 17 describes the parameters of this template The mean siz
36. of images within the data cubes In fact it is quite impressive to see how resistant aperture masking is to bad seeing the likelihood map presented in Figure 5 17 pinpoints precisely the position of the companion We recorded an angular separation of 59 8 mas with a flux ratio of 1 22 N 0 19 Additional on SAM scientific results can be found in the NaCo SAM web pages 5 6 13 PSF and MTF Informtion of PSF and MTF can be found in the NaCo SAM web pages http www eso org sci facilities paranal instruments naco inst sam html 5 6 14 Calculating Exposure times mask throughput and sensitivity for selected filters In order to convert from the standard CONICA exposure times given by the online calculator tool into SAM exposure data only two additional numbers are needed These are 1 the fraction of the mirror area passed by the mask and 2 the fraction of the total flux that will be found in the brightest pixel 53 NaCo User s Manual VLT MAN ESO 14200 2761 These numbers have been calibrated using the commissioning data for a subset of the total available filter mask combinations For filters which have not been calibrated here it should be fairly simple to extrapolate from these numbers to get reasonably close The table below gives mask areas and peak pixel flux ratios for all mask filter combinations used in commissioning 18Holes Total area 3 9 of pupil Filter Peak Pixel Flux NB 1 75 6 38e 4 IB 2 24 6 10e 4 NB 3
37. offset for sky image DEC offset arcsec 5 DEC offset for sky image Position angle on sky 0 Position angle 0 Add Velocity Alpha Additional tracking velocity in arcsec sec Add Velocity Delta 0 Additional tracking velocity in arcsec sec Filter NODEFAULT Filter name e g Ks Neutral Density Filter ND_Shott Neutral density Filter Full none Camera NODEFAULT Camera Name e g S27 Slit NODEFAULT Slit name NAOS parameter file NODEFAULT NAOS aocfg file from JNPS 7 3 5 NACO img acq MoveToMask This template does a telescope preset and is followed by interactive centting of the object behind the coronagraphic mask It is very similar to the NACO img acq MoveToPixel template however it must be followed by a coronagraphic template drawing of the selected mask is displayed on the RTD and is superimposed on the image of the field The centting of the target is then done interactively Acquisition must be done with the L27 objective for LW filters and can be done with either the S13 or S27 objectives for SW filters For precise centring with the 4QPM mask we recommend that users use the S13 objective Note that when 4QPM masks are used the mask itself is not taken out of the optical path as was the case in the past to avoid repositioning problems Table 7 5 describes the parameters of this template This template records either two or four images If two images are recorded then the first image is an image of the approximately
38. recommend that you consult the NaCo web pages for the latest information o All imaging observations must use the NACO img acq MoveToPixel template for acquisition o All polarimetric observations must use NACO img acq Polarimetry for acquisition o All spectroscopic observations must use NACO img acq MoveToSlit for acquisition o All coronagraphic observations must use NACO img acq MoveToMask for acquisition o All observations with the SDI must use NACO img acq SDIMoveToPixel for acquisition o All observations with the SDI 4 must use NACO img acq SDIMoveToMask for acquisition o Al observations with SAM must use NACO img acq SAMMoveToPixel for acquisition o It is possible to submit a single OB that comprises several observing descriptions for example one can observe a single target with different filters but most mixed mode observations e g coronagtaphy with spectroscopy ate generally not allowed Direct imaging after any other mode is allowed but users should note that the position of the object in the CONICA FOV will slightly change when moving from either coronagraphy or spectroscopy to imaging because different flexure compensation models are used for these modes O Some targets we are asked to observe saturate the detector with the minimum DIT Consult the ETC o The pixel scale is very small so the readout noise can dominate if the DIT is too small Consult the ETC o In the NACO spec obs AutoNodOnsSlit template the jitter wi
39. slitless spectroscopy the latter in VM only together with 4 grisms of resolving power 400 1400 Polarimetry Imaging with a Wollaston prism SAM Sparse Aperture Interferometry with 4 different masks VM only This manual is organized as follows e Sec 3 a summary of AO techniques and IR observations Sec 4 description of NAOS Sec 5 description of CONICA Sec 6 operations with NaCo Sec 7 acquisition and observations templates manual Section 8 filters transmission curves e Section9 the Preparation Software PS user manual 12 NaCo User s Manual VLT MAN ESO 14200 2761 Additional resources NaCo Web Pages NaCo Online Documentation NaCo News NaCo Call for Proposal NAOS Preparation Software Exposure Time Calculator Catalogues for adaptive optics reference objects http www eso org instruments naco http www eso org instruments naco doc http www eso org instruments naco news html http www eso org sci observing proposals http www eso org observing p2pp OSS NAOSPS http www eso org observing etc Optical sources ESO GSC2 skycat http archive eso org skycat GSC2 at STScI http www gsss stsci edu Infrared Sources VIZIER Catalogue http vizier u strasbg fr viz bin VizieR source 2MASS Phase 2 Proposal http www eso org observing p2pp NaCo NaCo P2PP html Preparation User Support Department NaCo Quality Control http www eso org org dm
40. spectral bands it is therefore possible to identify the position of the secondary star The position is indicated by the two arrows in Figure 5 16 Data fitting also allows derivation of the flux ratio between the star and its companion These results are summarised in Table 5 9 Table 5 9 result of the observations of AB Dor and its calibrator Star AB Dor AB Dor HD 39213 Wavelength K H K ARA mas 183 6 192 9 19 8 ADec mas 75 6 77 8 56 8 Relative flux 1 20 N 0 14 1 47 0 24 1 22 0 19 Delta mag 4 71 0 15 4 58 02 4 78 0 17 Our results on AB Dor are in agreement with the results obtained by coronagraphic means and with results from the literature see Janson et al A amp A 462 615 2007 Sources of potential errors are 1 Uncertainty on the orientation on the field of view on the pupil Aperture masking require freezing the spider arms in the pupil plane vertical mode The field orientation on the detector is therefore changing with time which requires further sophistication of the software because the recorded data header values become inaccurate 2 Uncertainty on the central wavelength due to the spectral type of the target 3 Uncertainty on the pupil diameter inside the camera filter wheel These sources of error at present limit the determination of the relative positions to a few percent a value which should improve with further characterization 52 Na
41. standard practice is to resort to the jitter technique and most NaCo imaging templates make use of it The technique basically consists of taking numerous images of the field typically 10 or more with small offsets between the positions The sky is then estimated from all the observations The most critical aspect of jittering is that the size of the offsets should be larger than the spatial extent of the object s one is observing For more crowded fields or extended objects i e covering a large fraction of the array the jittering technique works less well and the sky has to be sampled separately from the object resulting in a loss of observing efficiency which can amount to 50 of the time if the sky has to be sampled as frequently as the object Still all the object positions can be jittered between themselves as well as the sky positions This minimises the effect that poor array cosmetics have on the data In the case of crowded fields where there is no suitable nearby sky field the jittering technique can still give good results as long as the number of offsets is large i e greater than 20 In spectroscopy the classical technique is to observe point sources or moderately extended sources at two or more positions along the slit allowing one to integrate continuously on the object For crowded fields or extended objects the sky has to be sampled separately from the object At thermal IR wavelengths gt 3 um the background i
42. that have a separation of 25 SDI 0 SDI 25 and SDI 5 SDI 30 and SDI 10 SDI 35 etc up to SD1 25 SD1 50 Adding them after having rotated them by the right amount will add up the information of the companion However we have only added 6 times the information of the companion while we have a total of 11 images and subtracted out 6 images To add up the other 5 images we can for example subtract from the 38 NaCo User s Manual VLT MAN ESO 14200 2761 5 images that have not been added yet SDI 30 to SDI 50 note that they were used for subtraction though the images that show an angle difference of 25 SDI 50 SDI 25 SD1 45 SDI 20 etc to SD1 30 SDI Adding all these roll subtracted images corrected for the instrument angle will create a typical spatial structure made of a positive PSF at the companion position and 2 negative PSF located at 25 on each side of the companion The profile in Figure 5 12 clearly shows an improvement of about 1 mag with respect to standard SDI data reduction SDI 2 rolls 10 4Q 4Q ref 3 4th of the dato SDI SDI roll SOl ref 3 4th of the doto 107 SDI ref roll 3 4th of the ous SDI Stondord roll subtraction 2 deg SDI double roll subtraction 25deg 10 Hi 5 g detection level 107 107 0 0 0 5 1 0 1 5 2 0 Angular distance in arcseconds Figure 5 12 5 0 detection level for different processing techniques 4Q and
43. the detector mode is set to HighDynamic The minimum DITs for these modes are listed in Table 5 11 For very bright targets a neutral density filter can be inserted into the light path The choices are Pull for no neutral density filter ND_Long for a LW neutral density filter and ND_Short for a SW neutral density filter Filter curves are plotted in Section 8 All acquisition templates can be used to acquire PSF stars In such cases the PSF reference T F flag should be set to true Although the NAOS configuration will be ignored during the acquisition a valid NAOS parameter file is still required By default the PSF reference T F flag is F Note that this flag when used with pupil tracking including SAM will additionally keep the pupil angle fixed 7 3 1 Pupil Tracking PT in the acquisition templates Pupil tracking is set in the acquisition template and it can be set to true only for those templates that support this feature NACO img acq SAMMoveToPixel NACO img acq SDIMoveToPixel NACO img acq SDIMoveToMask NACO img acq MoveToPixel NACO img acq MoveToMask In those templates the rotator angle assumes a different meaning since the pupil tracking flag has been set to T it is the angle to which the telescope spiders should be set In the remaining templates NACO img acq MoveToSlit and NACO_img_acq_Polarimetry even though the flag is still present it must remain set to F Rotator angle offsets work the same way as in normal r
44. the studied star is doubled for a given observing time For this reason we advise users to save images with rotation steps of the instrument and use this double roll subtraction technique to improve the efficiency of the instrument In terms of operations the rotation of the instrument is already implemented in the templates and is not time consuming However during the rotation the position of the star is changed compared to the coronagtaph mask and a re centring is mandatory albeit time consuming 5 3 3 Calibration plan for SDI 4 Darks with the same DIT are the only supported calibration 5 3 4 Night flat fields for SDI 4 SDI 4 is even more affected by dust than those of 4QPMs The same recommendations issued for 4QPMs hold for SDI 4 Imperfections on the plates that hold the 4QPMs together with instrument flexure means that flat fields depend on the rotator angle For this reason the template NACO_coro_cal_NightCalib allows one to take nighttime flat fields immediately after SDI 4 data have been taken We strongly recommend that these calibrations are taken for the said setup In addition the acquisition template for SDI 4 NACO img acq SDIMoveToMask takes the following calibration frames o One flat on and one flat off images with the mask inserted Those can be used for flat fielding of the science data taken afterwards since the mask is not moved out of the beam o Two images of the bright star off the mask with ND Shott inser
45. to an angle of M 2D and the extracted PSF is assumed to be monochromatic To access the PSF data once the optimization has been performed click on the PSF button This pops up a window that shows the profile of the PSF 118 NaCo User s Manual VLT MAN ESO 14200 2761 along the x and y axes Figure 9 6 The FITS file itself can also be saved to the user s local disk for later use If you want to save the file the Save PSF button brings a file browser and allows you to choose the name of the file on your local disk This operation is performed by sending the appropriate request to the central server where your PSF file has been stored under a unique name Depending on your local installation the file retrieval may take a few seconds The other quantities which are outputs of the optimization are o The Strehl ratio is expressed as a percentage It is derived from the PSF and as such it is linked to the observing wavelength The on axis Strehl ratio gives an estimate of the correction of the optical beam in the direction of the reference object i e as seen from the wavefront sensor in NAOS Conversely the off axis Strehl ratio is computed from the estimated PSF on the science object which allows one to estimate the correction provided by NAOS for the target o The full width at half maximum of the PSF is given in arcsec both in the main panel and in the pop up window depicted in Figure 9 6 o Transmission to CONICA is expressed as
46. user we will consider that the OB has been successfully completed in the event that all other constraints are met satisfactorily We are considering a similar classification scheme for the LGS operation Check for updates on the NaCo webpages http www eso org instruments naco news html 6 11 PSF reference star Observations of PSF stars are frequently used in the analysis of AO data Generally speaking the instrument set up should not change between the observation of the science target and the PSF reference the brightness of the two should be similar and atmospheric conditions should be stable With NAOS CONICA the simplest way of ensuring that the instrument configuration does not change is to ensure that the PSF reference T F flag in the acquisition template is set to T When this flag is T the telescope will preset to the target the operator will acquire the target and AO will start without changing the NAOS configuration The time required for PSF reference star observations will be charged to the user For service mode observations we request that all PSF reference OBs are prefixed with the string PSF_ and that clear instructions are written in the README file and the Instrument Comments fields for the science and PSF OBs 6 12 Recommended DIT and NDIT s Unless the object is bright enough to cause saturation Table 5 11 DITs need to be somewhat larger than those used in ISAAC because the NaCo plate scale is considerably
47. via the regular web based interface http www eso org observing etc or via the HTML file produced by PS Finally in the course of the execution of the observations at the telescope the PS is able to take into account the current external conditions and actual reference instead of expected source characteristics to optimize the observations still respecting the astronomer s requirements for observing wavelength transmission and so on The FTTS headers of NaCo data contain all the necessary information on the setup used Users can select the WFS directly This will allow users to use the N90C10 dichroic as neutral density filter for CONICA when using the visual WFS Additionally we have updated some parameters to better reflect the average conditions of the atmosphere above Paranal 9 1 Starting the PS The NAOS Preparation Software can be downloaded for a number of computer platforms at the following URL http www eso org observing etc naosps doc After installation a link to the general server situated at ESO will be required i e the local computer has to have access to the Internet In principle JNPS will work within any Java Virtual Machine which supports Java Development Kit DIS 1 5 0 or later It has been reported to work using a variety of Unix and Linux flavors as well as MacOs X Until further notice ESO will only officially support JNPS under Scientific Linux 4 3 The PS client is started by typing the command j
48. wave plate to its default position i e 0 The angles in the list of half wave plate angle are relative one from the other e g 0 22 5 22 5 22 5 would correspond to an absolute rotation of 0 22 5 45 67 5 Note that the first angle provided is absolute since the HWP is always set to its zero position at the beginning of the template Once the template has run over the list of half wave plate angles the telescope can offset according to a user defined list Spatial offsets are defined with the parameters List of offsets in X and list of offsets in Y The offsets are relative to the previous position are in X and Y and are defined in arcsec Additionally the observation type can be defined for each image and is entered as a list in the parameter Observation Type O or S O stands for Object and assigns the DPR TYPE header keyword to OBJECT S stands for Sky and assigns the DPR TYPE header keyword to SKY The AO loop is closed for the former and open for the latter The total number of spatial offsets is defined by the parameter Number of offset positions This number can be different from the number of elements in the aforementioned lists If the number of spatial offsets is larger than the number of elements in a list the list is restarted from the 100 NaCo User s Manual VLT MAN ESO 14200 2761 beginning as many times as needed until the correct number of offsets have been done These lists can have any length how
49. x NEXPO per offset position x Number of AB or BA cycles Thus the total integration time on the sky and on the object can be adjusted so that the S N on the object is optimised Remember that the 30 second per telescope position rule means here that both DIT x NDIT for the OBJECT positions x NEXPO per offset position plus overheads and DITx NDIT for the SKY positions x NEXPO per offset position plus overheads shall each exceed 30 seconds of time Table 7 14 Parameter of NACO_img_obs_FixedS ky Offset P2PP Label Default Values Description DIT NODEFAULT Detector Integration Time sec Readout mode Double_RdRstRd Readout mode Window Size 1024 Size of the window Store Data Cube T F F Data cube flag Jitter box width NODEFAULT Jiter Box Width Number of AB or BA cycles NODEFAULT One cycle is one object sky pair NDIT per object position NODEFAULT Number of DITs for the OBJECT NDIT per sky position NODEFAULT Number of DITs for the SKY NEXPO per offset position 1 Number of exposures per offset position Number of offset positions NODEFAULT Number of offset positions Sky offset in RA NODEFAULT RA offset in arcsec Sky offset in DEC NODEFAULT Dec offset in arcsec Filter NODEFAULT Filter name Neutral Densty Filter Full Neutral density filter Full none Camera NODEFAULT Camera Name Figure 7 6 illustrates how this template can be used 91 NaCo User s Manual VLT MAN ESO 14200 2761 NACO img obs FixedSkyOffset D
50. 1 50 0 0 0 5 1 0 1 5 2 0 arcsec from primary Figure 5 3 Contrast obtained on AB Dor with the new Wollaston SDI O AB_Dor H 4 84500 DX_leo H 5 24200 GJ799A H 5 20100 lH GJ799B H 5 20000 7 GJ803 H 4 83100 meee GJ862 H 5 28500 HD155555AB H 4 90700 _ HD181321 H 5 05000 D HD48189A H 4 74700 H 5 15600 a oe 5 31000 LL lt 0 0 0 5 1 0 1 5 2 0 arcsec from primary Figure 5 4 obtained on AB Dor with the old Wollaston SDI from Biller et al 2007 30 NaCo User s Manual VLT MAN ESO 14200 2761 5 1 8 Pipeline for SDI The SDI mode of CONICA is not supported by either a pipeline or an ETC 5 2 Coronagraphy For coronagtaphic applications a Lyot type coronagraph with a circular focal plane mask and an undersized pupil plane mask can be rotated into the beam of CONICA Five masks are available two opaque masks with diameters of 0 7 and 1 4 arc seconds a semi transparent mask with a diameter of 0 7 arc seconds and two 4 quadrant phase masks 4QPM one optimized for K band observations and the other for H band The available masks and their characteristics are listed in Table 5 4 Table 5 4 CONICA s masks for coronagraphy Name Diameter Comments C_0 7 0 7 Opaque held in place by wires 100 extinction over the mask C
51. 24 2 27 0 49 1400 S54_ 3 SK 1 79 2 57 2 54 1 00 1400 S27 3 SK 2 02 2 53 2 27 0 50 1400 54 4 SK 1 79 2 57 1 54 1 96 700 L54 1 SL 2 60 4 20 2 54 3 16 700 tr SE 2 60 4 10 2 27 1 57 700 L54_2_SL 3 02 4 20 1 54 2 01 1100 L27_2_SL 3 47 4 20 1 27 1 00 1100 L27_1_L 3 20 3 76 2 27 1 60 700 L54 2_L 3 20 3 76 1 54 2 00 1100 L27 AEP 3 50 4 10 2 At 1 60 700 L54_2_LP 3 50 4 10 1 54 2 00 1100 L27_2_LP 3 50 4 10 1 27 1 00 1100 Light from the second order can also be seen but does not contaminate 2 3rd order overlap at 3 90 microns 41 NaCo User s Manual VLT MAN ESO 14200 2761 5 4 1 Prism spectroscopy It is possible to do prism spectroscopy in the range 1 5 microns There are three spectroscopic modes with the prism See Table 5 6 The spectral resolution varies from about 40 in the J band to 250 in the M band The L27 P1 mode is difficult to use The resolution in J is very low and the background in M is high although it is not so high that normal readout modes cannot be used For targets with blue colouts it will be difficult to get good S N at 5 microns without saturating the spectra at 1 micron Data for the S27 P1 have not been taken Table 5 6 Prism spectroscopic modes Mode Filter Dispersion Wavelength R Fit Fit RMS Name nm pixel microns Order nm L27_P1 None 8 527 0 85 5 5 90 3 10 L27_P1 None 6 33 0 85 5 5 250 5 29 S13_P1
52. 74 1 12e 3 NB 4 05 1 26e 3 9Holes Total area 12 1 of pupil Filter Peak Pixel Flux NB 1 75 1 53e 3 IB 2 24 1 18e 3 NB 3 74 4 42e 3 NB 4 05 3 55e 3 4 75e 3 BB 9Holes Total area 8 7 of pupil Filter Peak Pixel Flux H 1 53e 3 Ks 1 37e 3 Lp 2 95e 3 Mp 2 72e 3 7Holes Total area 16 of pupil Filter Peak Pixel Flux H 2 67e 3 Ks 2 53e 3 Lp 5 52e 3 Mp use Lpvalue These values have been converted into expected count rates using the throughputs from the online sensitivity calculator Plots below give expected peak throughput for various mask filter and integration time combinations Information is organized by the various masks with each plot applying to a separate mask configuration The different CONICA narrowband interference filters ate indicated with different colored linetypes For each mask filter the expected peak counts received is given for a range of different exposure times starting with the shortest possible for subframes up to 10 second integrations The chip nonlinear regime begins with the horizontal line neat the top and saturation is at the very top 54 NaCo User s Manual VLT MAN ESO 14200 2761 Figure 5 18 Throughput for the 18 Holes mask Left panel shows throughput with three narrowband filters in J H and K bands respectively while the longer wavelengths are given to the right panel Various integration times are shown annotated on the plot Figure 5 19 Same as Figure 5 18 but
53. 8 5 1 4 PIPELINE FOR IMAGING 28 5 1 5 FABRY PEROT IMAGER 28 5 1 6 SIMULTANEOUS DIFFERENTIAL IMAGING SDI 28 5 17 SDI ON SKY PERFORMANCE 29 NaCo User s Manual VLT MAN ESO 14200 2761 5 1 8 PIPELINE FOR SDI 5 2 CORONAGRAPHY 5 2 1 5 2 2 5 2 3 5 2 4 5 2 5 5 2 6 5 2 7 5 2 8 5 2 9 PERFORMANCE OF THE SEMITRANSPARENT MASK C_0 7_SEP_10 PERFORMANCE OF THE 4QPMS RADIAL ATTENUATION OF 4QPMS CONTRAST OF 4QPMS CHROMATICITY OF 4QPMS COMPARISON WITH THE CLASSIC LYOT MASKS OBSERVATION STRATEGY WITH THE 4QPMS CALIBRATION PLAN FOR CORONAGRAPHY NIGHT FLAT FIELDS FOR CORONAGRAPHY 5 2 10 PIPELINE FOR CORONAGRAPHY 5 3 SIMULTANEOUS DIFFERENTIAL IMAGING PLUS CORONAGRAPHY SDI 4 5 3 1 5 3 2 5 3 3 5 3 4 5 3 5 5 4 5 4 1 5 4 2 5 4 3 5 4 4 5 4 5 5 4 6 5 5 5 5 1 5 52 5 6 5 6 1 5 6 2 5 6 3 5 6 4 5 6 5 5 6 6 5 6 7 5 6 8 5 6 9 CONTRAST WITH SDI 4 TESTS WITH 4QPM SDI 4 AND ROTATION CALIBRATION PLAN FOR SDI 4 NIGHT FLAT FIELDS FOR SDI 4 PIPELINE FOR SDI 4 GRISM SPECTROSCOPY PRISM SPECTROSCOPY SLITS CALIBRATION PLAN SPECIAL NOTES ABOUT THE PRISM CALIBRATION NIGHTTIME ARCS AND FLAT FIELDS PIPELINE FOR SPECTROSCOPY POLARIMETRY CALIBRATION PLAN FOR POLARIMETRY PIPELINE FOR POLARIMETRY SPARSE APERTURE INTERFEROMETRIC MASKS SAM SAM WHY AND WHEN TO USE IT PUPIL TRACKING WITH SAM DETECTOR READOUT AND CUBE MODE SETUP FOR SAM SAM WITH LW FILTERS CHOOSING WHICH MASK TO USE
54. CO POL OBS RETARDER 7 73 NACO POL CAL STANDARDSTAR 7 8 NACO CORONAGRAPHIC SCIENCE TEMPLATES 76 78 79 79 80 80 81 81 82 83 84 85 86 86 86 88 90 90 92 93 93 93 94 94 96 98 98 98 98 100 102 102 NaCo User s Manual VLT MAN ESO 14200 2761 7 8 1 NACO CORO OBS STARE 102 7 8 2 NACO CORO OBS ASTRO 103 7 8 3 NACO CORO CAL NIGHTCALIB 105 7 8 4 NACO CORO CAL STANDARDSTAR 105 7 9 NACO SDI 4 SCIENTIFIC TEMPLATES 106 79 1 NACO SDI4 OBS STARE 106 7 10 NACO SAM SCIENCE TEMPLATES 107 7 10 1 NACO SAM OBS GENERICOFFSET 107 8 FILTER TRANSMISSION CURVES 109 8 1 CONICA BROAD BAND IMAGING AND ORDER SORTING FILTERS 109 8 2 CONICA NEUTRAL DENSITY FILTERS 109 9 PREPARATION SOFTWARE 111 9 1 STARTING THE PS 111 9 2 GRAPHICAL USER INTERFACE OVERVIEW 111 9 3 TARGET AND INSTRUMENT SETUP 112 9 4 SKY CONDITIONS 113 9 5 REFERENCE OBJECTS 113 95 1 HANDLING SEVERAL REFERENCE OBJECTS 113 9 5 2 MORPHOLOGY 114 95 3 PHOTOMETRY 115 9 5 4 TRACKING TABLE 115 9 5 5 OPTIMIZING NAOS AND GETTING A PERFORMANCE ESTIMATION 116 9 5 6 EXPORTING TO THE EXPOSURE TIME CALCULATOR 119 9 5 7 EXPORTING TO P2PP 120 9 5 8 EXPORTING OBS FROM P2PP 120 9 5 9 SAVING RESTORING A PS SESSION 120 9 5 10 GIVING NAMES TO SESSION P2PP AND PSF FILES 120 9 5 11 USER S PREFERENCES 120 NaCo User s Manual VLT MAN ESO 14200 2761 LIST OF TABLES Table 4 1 NaCo dichroics beamsplitters 20 Table 4 2 Wavefront sensors characteristics 21 Table 4 3
55. Co User s Manual VLT MAN ESO 14200 2761 5 6 12 On sky observations HD39213 in K EET pp ap 7 140 200 m L E of Q Ke 5 200 L p f 132 400 l u M adda 400 200 0 200 400 RA mas Figure 5 17 Likelihood as a function of the position of a secondary star At maximum likelihood the flux ratio between the main stat and its companion is 1 22 0 19 arrow AB Dor was an excellent commissioning target since it allowed a validation of the technique with respect to the coronagraphic results However it is not an excellent target to demonstrate the possibilities offered by aperture masking This technique is more adapted for imaging details which are within the speckle noise range Typically it shows an important advantage for high dynamic range imaging close to the main star 1 to 5 A d We therefore observed HD 39213 This star has a close companion with a flux ratio of the order of a few percent and an angular separation of less than 100 mas HD39213 was observed from 2h22 to 2h45UT The calibrator HD 39545 was observed between 2h48 and 3h12UT H band and K band data consist of 2 data cubes of 24 images of 8 seconds exposure time Due to a longer integration time and because the seeing degraded notably averaging 1 8 H band data were mostly useless We were nevertheless able to retrieve useful information from the K band data by careful selection
56. CutOff 2 5um 4 1 0 85 2 50 60 3 10 S27_P1 CutOff 2 5um 8 2 0 85 2 50 60 5 4 2 Slits Two long slits and a slitless mode are available for spectroscopy The characteristics are listed in Table 5 7 Slitless spectroscopy is done with the FLM_13 mask which is the field mask used for imaging with the 13 objective and it is available for the SW grism modes only The centring of the observed object in the slit or to the center of the mask in the case of slitless spectroscopy is done interactively through an acquisition template Table 5 7 Slits in CONICA Name Dimensions Comments Slit 86mas 86mas x 40 For the S27 and L27 the slit length is 28 Slit_172mas 172mas x 40 For the S27 and the L27 the slit length is 28 Slitless 14 x14 Only used for SW modes 5 4 3 Calibration plan For spectroscopic observations a variety of calibration frames will be taken archived and updated at regular intervals The calibrations are described in detail in the NaCo Calibration Plan o Telluric Standard Stars Observations of telluric standards will be performed whenever the grisms are used Whenever possible we will limit the airmass difference between the standard and science target to 0 1 airmasses The standard will be observed with the setup Based on the 86 mas slit on the central wavelength Fit based on spectra taken were taken with several narrow band filters to create pseudo arc lines Th
57. EC E Offset Sky Positions Object Positions RA Offset Figure 7 6 An illustration of how the NACO img obs FixedSkyOffset template works with Jitter Box Width 9 Number of AB or BA cycles 4 Sky offset in Dec 15 Sky offset in RA 35 Return to Origin I F T Camera S13 The AO loop is off when the sky is observed large filled in circles and on when the object is observed small filled in circles The dashed line connecting 8 with 1 is the offset done at the end of the telescope since Return to Origin T F is set to T The dashed box is defined by the Jitter Box Width 7 4 5 NACO img cal StandardStar This template is used for imaging standards and is similar to the NACO img obs GeneticOffset template with the difference that some DPR keywords in the FITS headers of the images are set to different values allowing pipeline processing and archiving Additionally NDIT is single valued in this template and offsets are in detector coordinates only This template should be used by all users who wish to take calibrations standard stars observation beyond the ones provided by the Calibration Plan Table 7 15 describes the parameters of this template Table 7 15 Parameters of NACO img cal StandardStar P2PP Label Default Values Description DIT NODEFAULT Detector Integration Time sec NDIT NODEFAULT Number of DITs Readout mode Double_RdRstRd Readout mode Window Size 1024 Size of the window Store Data Cube T
58. EUROPEAN SOUTHERN OBSERVATORY Organisation Europ enne pour des Recherches Astronomiques dans I H misphere Austral Europ ische Organisation f r astronomische Forschung in der s dlichen Hemisph re VERY LARGE TELESCOPE NaCo User Manual Doc No VLT MAN ESO 14200 2761 Issue 82 1 Date 20 06 2008 Prepared P Amico N Ageorges C Lidman 20 06 2008 Name Date Signature Approved O Hainaut Name Date Signature Released A Kaufert NameA Date Signature CHANGE RECORD ISSUE DATE SECTIONS REASON INITIATION AF ECTED DOCUMENTS REMARKS First issue 31 7 2001 New 82 1 26 2 2008 New revisited version Changed list of authors Porting to doc pdf Introduction of cube SAM and pupil tracking modes NaCo User s Manual VLT MAN ESO 14200 2761 TABLE OF CONTENTS 1 SCOPE 10 1 1 LIST OF ABBREVIATIONS amp ACRONYMS 10 2 INTRODUCTION 12 2 1 ADDITIONAL RESOURCES 13 2 2 CURRENT VERSION OF THE MANUAL 13 2 3 CHANGES FOR P82 13 3 OBSERVING WITH ADAPTIVE OPTICS IN THE INFRARED 15 3 1 ATMOSPHERIC TURBULENCE 15 3 2 ADAPTIVE OPTICS 15 3 3 INFRARED OBSERVATIONS WITH AN AO SYSTEM 16 3 4 TRANSMISSION AND BACKGROUND 17 3 5 BACKGROUND SUBTRACTION 17 3 6 SPECTROSCOPY 19 4 NAOS 20 4 1 OVERVIEW 20 4 2 NAOS PERFORMANCE 21 4 3 ANISOPLANATISM 22 4 4 LASER GUIDE STAR FACILITY LGSF 22 5 CONICA 24 5 1 IMAGING 25 5 1 1 CAMERAS 26 5 1 2 FILTERS 26 5 1 3 CALIBRATION PLAN FOR IMAGING AND SDI 2
59. FAULT Filter name Neutral Densty Filter Full Neutral density filter Full none Camera NODEFAULT Camera Name 88 NaCo User s Manual VLT MAN ESO 14200 2761 1024 1024 N Position Angle 45 deg CONICA FOV 28 for 27 1 1 x Figure 7 4 An illustration of how the NACO img obs GenericOffset template works In this example the offsets are in DETECTOR co ordinates Exposures 1 and 5 occur at the same place and the telescope will not return to the origin after the eighth exposure The parameter settings for this example were Table 7 11 parameters for the example shown in Figure 7 4 NEXPO per offset position 1 Observation Type O or S O Number of offset positions 8 Offset Coordinates DETECTOR Return to Origin I F F List of offsets in RA or X 030 300 30 Camera 27 List of offsets in DEC or Y 0070 7 707 1024 1024 N Position Angle 45 deg CONICA FOV 28 for 27 1 1 x Figure 7 5 A second illustration of how the NACO_img_obs_GenericOffset template works As with the previous example exposures 1 and 5 occur at the same place and the telescope will not return to the origin after the eighth exposure The parameter settings for this example were Table 7 12 parameters for the example shown in Figure 7 5 NEXPO per offset position 1 Observation Type O or S O Number of offset positions 8 Offset Coordinates SKY Return to Origin I F F List of offsets in RA o
60. Focus Y Deformable T mirror Dichroic Output Parabola Input Parabola a Tipftilt WFS Input Focus mirror VLT Nasmyth Focus Figure 4 1 A view of the NAOS optical train The DM which contains 185 actuators compensates for the higher order aberrations including the static aberrations of NAOS and CONICA Table 4 1 NaCo dichroics beamsplitters Dichroic Reflected light to the Efficiency Transmitted light Efficiency Use Name WES to CONICA VIS VRI 90 J H K L M 90 Near IR observations 0 46 0 95 um 1 05 5 0 um with optical WFS N20C80 VRLLHK 20 VRLLHK 80 WFS and observations 0 45 2 55 um 0 45 2 55 um in the IR N90C10 VRLLHK 90 VRLLHK 10 WFS and observations 0 45 2 55 um 0 45 2 55 um in the IR JHK LLHK 90 LM 90 Thermal IR 0 80 2 55 um 2 8 5 5 um observations and near IR WFS K K 90 V RLJ H 90 J H observations and K 1 9 2 55 um 0 45 1 8 um band WES The N90C10 dichroic can also be used with the visible WFS In this case it acts as a neutral density filter NaCo User s Manual VLT MAN ESO 14200 2761 A dichroic splits the light between CONICA and the WFS channel Each dichroic is associated with one WFS with the exception of the N90C10 For example the visual dichroic can only be used with the visual WFS and the other dichroics can only be used with the IR WFS The conditions under which the dichroics can be used are listed in Table 4 1 Use
61. GS observation type PSF Reference T F F Set to T if it is a PSF reference star Pupil Tracking Mode T F F Set to true for PT observations RA offset arcsec 5 RA offset for sky image DEC offset arcsec 5 DEC offset for sky image Position angle on sky 0 Position angle or pupil angle in degrees Add Velocity Alpha 0 Additional tracking velocity in arcsec sec Add Velocity Delta 0 Additional tracking velocity in arcsec sec Filter NODEFAULT Filter name e g Ks Neutral Density Filter Full Neutral density Filter Full none Camera NODEFAULT Camera Name e g S27 NAOS parameter file NODEFAULT NAOS aocfg file from JNPS 7 3 3 NACO img acq SDIMoveToPixel This template is very similar to NACO img acq MoveToPixel 7 3 2 with the exception that the camera and the filter are not parameters of the template It should only be used to acquite targets for SDI The template does a telescope preset and is followed by interactive centring of the object It must be followed by an SDI template In service mode it is mandatory that users provide detailed information for the field centring on their Finding Charts and or in their README file In order for faint objects to be clearly seen an image of the sky is acquired in an offset position defined by the RA offset arcsec and DEC offset arcsec parameters The image is then subtracted from all images that are subsequently displayed on the RTD The integration time for these acquisition imag
62. Integration Time 20 min Execution Time min Preset 3 Guide Star Acquisition 0 75 Initial Setup 2 AO Acquisition 5 Coronagraphic acquisition 2 Sub Total acquisition 12 75 Observation 20x 1 3x60 27 35 Total min 48 Overheads 140 Observation Integration time minutes x 1 30 x 60 sec Offset Overhead 74 NaCo User s Manual VLT MAN ESO 14200 2761 Table 6 14 Example 8 Imaging with chopping Template parameters Acquisition Template NACO_img_acq_MoveToPixel Observation Template NACO img obs AutoChopNod Integration Time 20 min Execution Time min Preset 3 Guide Star Acquisition 0 75 Initial Setup 2 AO Acquisition 5 Imaging acquisition 0 5 Sub Total acquisition 11 25 Observation 20x 1 3x60 27 35 Total min 46 Overheads 130 Observation Integration time minutes x 1 30 x 60sec Offset Overhead Table 6 15 Example 9 A bright source with SDI Template parameters Acquisition Template NACO img acq SDIMoveToPixel Observation Template NACO sdi obs GenericOffset DIT 10 sec NDIT 6 Number of offset positions 5 NEXPO per offset position 1 Readout Mode Double R dRstRd List of position angle ffsets 0 33 Return to original rotator postion F Execution Time min Preset 3 Gu
63. Number of exposures on sky only Sky offsets in RA NODEFAULT RA offset in arcsec Sky offsets in DEC NODEFAULT DEC offset in arcsec 7 10 NaCo SAM science templates At the time of writing the SAM template is still under construction Changes to these instructions will be posted in the manual and the web pages as soon as they are known SAM is only offered in VM and visitor are encouraged to contact the NaCo Team naco eso org ahead of their run for any questions 7 10 1 NACO sam obs GenericOffset The science template is similar to NACO img obs GenericOffset Note that however not compulsory SAM will use cube mode for data storage as a default This and the handling of the offsets in pupil tracking mode account for most of the differences with the NACO_img_obs_GenericOffset 107 NaCo User s Manual VLT MAN ESO 14200 2761 In the most basic mode ie recommended setup SAM will typically require a 512x514 subframe and observations will occur in pairs that are dithered between two separate quadrants e g bottom left top right Sky observations will be dealt with as usual open loop offset set by the user in the offset sequence Table 7 27 describes the parameters of this template Table 7 27 Parameters of NACO_sam_obs_GenericOffset P2PP Label Default Values Description DIT NODEFAULT Detector Integration Time sec Readout mode Double_RdRstRd Readout mode Window Size 1024 Size of the window Store Data Cu
64. OMMENDED MAGNITUDE RANGES FOR STANDARD STARS MAXIMUM BRIGHTNESS OF OBSERVABLE TARGETS 51 51 53 53 53 56 56 56 57 57 58 58 59 60 61 61 62 62 63 63 63 64 64 64 64 64 64 64 65 65 66 66 67 67 67 NaCo User s Manual VLT MAN ESO 14200 2761 6 16 NIGHTTIME CALIBRATIONS 6 17 INSTRUMENT AND TELESCOPE OVERHEADS 6 18 OBSERVING WITH THE LGS 7 NAOS CONICA TEMPLATES 68 68 69 76 7 1 GENERAL REMARKS AND REMINDERS 7 1 1 OFFSET CONVENTIONS AND DEFINITIONS 7 2 NACO GENERAL TEMPLATES 7 2 1 NACO ALL OBS ROTATE 7 3 NACO ACQUISITION TEMPLATES 7 3 1 PUPIL TRACKING PT IN THE ACQUISITION TEMPLATES 7 3 2 NACO IMG ACQ MOVETOPIXEL 7 3 3 NACO IMG ACQ SDIMOVETOPIXEL 7 34 NACO IMG ACQ MOVETOSLIT 7 3 5 NACO IMG ACQ MOVETOMASK 7 3 6 NACO IMG ACQ SDIMOVETOMASK 7 3 7 NACO IMG ACQ POLARIMETRY 7 3 8 NACO_IMG_ACQ_SAMMOVETOPIXEL 7 4 NACO IMAGING SCIENCE TEMPLATES 74 1 NACO IMG OBS AUTOJITTER 7 42 NACO IMG OBS GENERICOFFSET 7 43 NACO IMG OBS AUTOCHOPNOD 7 44 NACO IMG OBS FIXEDSKYOFFSET 7 45 NACO IMG CAL STANDARDSTAR 7 46 NACO IMG CAL CHOPSTANDARDSTAR 7 5 SIMULTANEOUS DIFFERENTIAL IMAGING SDI TEMPLATE 7 5 1 NACO_SDI_OBS GENERICOFFSET 7 6 NACO SPECTROSCOPIC SCIENCE TEMPLATES 7 6 1 NACO SPEC OBS AUTONODONSLIT 7 6 2 NACO SPEC OBS GENERICOFFSET 7 6 3 NACO SPEC CAL STANDARDSTAR 7 64 NACO SPEC CAL NIGHTCALIB 7 7 NACO POLARIMETRY SCIENCE TEMPLATES 77 1 NACO POL OBS GENERICOFFSET 7 7 2 NA
65. OS CONICA or for which the IR WFS provides a better correction 6 10 Measurement of Strehl Ratio and classification of OBs in Service mode SM To help the observatory determine whether or not an OB has been successfully executed in setvice mode the Strehl Ratio of the reference source will be measured with the NB 2 17 filter during acquisition The measurement during the acquisition process is automatic Users do not have to worty about it Depending on the morphology and brightness of the target the service observer will measure the Strehl ratio on the reference source and a preliminary classification will be made If the reference is extended too faint or too bright the measurement will not be made and the OB classification will be based on the performance that is computed by the RTC 65 NaCo User s Manual VLT MAN ESO 14200 2761 Alternatively the operator will try to measure the SR on the pipeline reduced images whenever suitable sources are available If the performance of the RTC cannot give a valid estimate which is the case for slow AO modes and no other measurements is possible the operator will report the seeing as seen by the guide probe which is more indicative of the actual observing conditions than the DIMM seeing measurement and indicate the values for other parameters of interest such as the coherence time If we believe that we have achieved a Strehl Ratio which is greater than 50 of that requested by the
66. S AO loop being closed at the end of the offset The second is an offset that results in the NAOS AO loop being opened at the end of the offset In the first case the field selector FS has to move from where it was when the NAOS AO loop was last closed In the second case the FS does not move The field of view of the FS is a bit less than 2 arcminutes If the offset sequence is such that the positions at which the loop needs to be closed is outside this region the observations will fail It is not possible for the system to know beforehand what offsets it will be asked to perform so if it encounters an offset command which would move the FS beyond its limits it will politely refuse Template parameters which would lead to that happening are checked for possible problems during OB verification 62 NaCo User s Manual VLT MAN ESO 14200 2761 When small telescope offsets are used less than one arc minute the telescope keeps the same active optics star If however large telescope offsets are used several arcminutes the active optics star changes Nevertheless when returning to the science target and closing the AO loop on the same reference source any offsets that might be caused by changing guide stars should be compensated by NAOS 6 5 Chopping and Counter Chopping For coronagraphic observations with the LW filters and imaging and polarimetric observations with the Mp filter chopping is the only offered mode For imaging
67. S or K 7 for the IR WFS with 12 NaCo User s Manual VLT MAN ESO 14200 2761 Table 6 10 Example 5 SW Polarimetry of bright source with the Wollaston Template parameters Acquisition Template NACO img acq Polarimetry Observation Template NACO pol obs GenericOffset DIT 10 sec NDIT 6 Number of offset positions 5 NEXPO per offset position 1 Readout Mode FowlerNsamp List of position angle offsets 0 45 Return to Origin F Execution Time min Preset 3 Guide Star Acquisition 0 75 Initial Setup 2 AO Acquisition 5 Polarimetric acquisition 1 Sub Total acquisition 11 75 Observations at 0 and 45 degrees 2x 5x 27 6x 10 2 2x8 3 16 4 Rotator offset in between angles 1 Total min 23 95 Overheads 193 5 Observation Number of offset positionsx Offset overhead NDIT DIT readout overhead Table 6 11 Example 5b Polarmetry of bright source with the Wollaston and HWP Template parameters Acquisition Template NACO img acq Polarimetry Observation Template NACO pol obs Retarder DIT 10 NDIT 6 Number of offset positions 5 NEXPO per offset position 1 Readout Mode FowlerNsamp List of HWP offses 0 22 5 Execution Time min Preset 3 Guide Star Acquisition 0 75 Initial Setup 2 Setting HWP in out 1 AO Acquisition 5 Polarimetric acquisition 1 Sub Total acquisiti
68. Summary of NaCo Strebl ratios at 2 2 microns for an AO reference star at an airmass of 1 2 22 Table 5 4 CONICA s masks for coronagraphy 31 Table 5 5 Spectroscopic modes The mode name consists of the objective the grism number and the order sorting filter 41 Table 5 6 Prism spectroscopic modes 42 Table 5 7 Slits in CONICA 42 Table 5 9 result of the observations of AB Dor and its calibrator 52 Table 5 10 CONICA detector characteristics 57 Table 5 11 CONICA detector readout modes 59 Table 5 12 characteristics of cube mode 60 Table 6 1 Recommended DIT and NDIT range 66 Table 6 2 IR Backgrounds The hyphens mark invalid combinations of a NAOS dichrow CONICA filter 67 Table 6 3 Recommended magnitude range of standard stars for observations with the visual dichroic 67 Table 6 4 Magnitude limits for DIT lt 1 sec 67 Table 6 5 NaCo Overheads 70 Table 6 6 Example 1 Imaging a faint source V 15 for visual WFS or K 10 for IR WFS with FowlerNsamp 71 Table 6 7 Example 2 Imaging a bright source V 11 with the VIS WES or K 7 with the IR WFS with Double_RdRstRd 71 Table 6 8 Example 3 Imaging a bright source in the L band V 11 for the VIS WFS or K 7 for the IR WES with Uncorr 72 Table 6 9 Example 4 Spectroscopy of faint source with FowlerNsamp 72 Table 6 10 Example 5 SW Polarimetry of bright source with the Wollaston 73 Table 6 11 Example 5b Polarmetry of bright source with the Wollaston and HWP 73 Table 6 12 Example 6
69. aCo User s Manual VLT MAN ESO 14200 2761 Table 5 11 CONICA detector readout modes for each astronomical use the mode Readout Noise RON gain full well FW capacity and minimum DIT min DIT are given Instrument Readout mode Detector Mode RON Gain Full Min mode ADU e ADU Well DIT ADU sec SW FowlerNsamp HighSensitivity 1 3 12 1 7500 1 7927 SW Double RdRstRd HighDynamic 4 2 11 0 15000 0 3454 LW NB Uncottr HighDynamic 4 4 11 0 15000 0 1750 imaging LW Lp imaging Uncott HighWellDepth 4 4 9 8 22000 0 1750 LW Mp Uncotr HighBackground 4 4 9 0 28000 0 0560 imaging Full Well refers to the full well depth In this case the array is completely saturated and photometry cannot be done Generally users should keep the peak count to below two thirds of the full well depth For exposures with DITs that are within a factor of a few of the minimum DIT the well depth is reduced by a factor of approximately two because of the readout overhead In Mp imaging the array is windowed 5 8 Cube mode Cube mode Tentatively offered pending commissioning this mode is a variant of the burst mode already offered with VISIR and ISAAC In this mode a data cube with each single DIT frame is saved This mode is particularly interesting for lucky imaging type of observations where one wants to select the best frames out of a set before co adding them The mode is not suited for time res
70. aging part of the template where no coronagraphic mask is used DIT IMG amp NDIT IMG can be defined independently of the rest of the template Similarly the number of exposures per position NEXPO IMG and the number of offsets NOFF IMG are free parameters I IT Coronography Generic Offset Coronography on target on sky Figure 7 11 Illustration of how the NACO coto obs Astro template works The 3 phases of the template are presented Part I left coronagraphy without moving the telescope Part II middle simple imaging the coronagraphic mask is removed Normally the first offset is zero to measure the exact position of the target out of the mask The last offset of the list NOFF SKY bring you onto the sky position where the original coronagraphic mask is inserted again and on sky coronagraphic images are taken in open loop Part III right diagram In this example NOFF SKY 5 Table 7 23 describes the parameters of this template The total integration time excluding overheads is defined in seconds by the sum of the CORO time and IMAGING time time spent on each mode respectively CORO exposure DIT CORO x NDIT OBJ x NEXPO OBJ DIT CORO x NDIT SKY x NOFF SKY IMG exposure DIT IMG x NDIT IMG NEXPO IMG NOFF IMG When using the 4QPM masks if no neutral density filter is needed it is recommended to use the Full_Uszd mask 104 NaCo User s Manual VLT MAN ESO 14200 2761 Table 7 23 Parame
71. andwidth filter sets In terms of optical throughput this therefore gives a double penalty The use of the more closely ideal masks many tiny holes is therefore restricted to quite bright targets The primary determinant for which mask to choose in any given situation is the brightness of the stellar target For bright targets try for a mask with many small holes 18Holes For faint targets a mask with fewer large holes and the ability to observe in the broad filter sets e g BB_9Holes is likely more optimal There can also be secondary issues motivating the choice of a mask In general to get enough Fourier coverage to do good mapping of a complex structured target one should push for a mask with more holes and short minimum baselines to extend the field of view Furthermore some observations may be needed in specific narrowband filters or with special setups and so mask choice can be a complex optimization The four commissioned masks are now briefly described in turn More detailed specifications and hole layouts are given in http www eso org sci facilities paranal instruments naco inst mask_datasheet html 18Holes This mask can only be used with the narrow and intermediate NB IB filter sets Useful range is targets brighter than about 4 Mag Excellent Fourier coverage for imaging and should also serve well for faint companion detection 9Holes This mask is designed for use with the NB and IB filters although it
72. arameters List of offsets in X and List of offsets in Y They are relative to the previous position are in detector co ordinates and are defined in arcsec Additionally the observation type can be defined for each image and is entered as a list in the parameter Observation Type O or S O stands for Object and assigns the DPR TYPE header keyword to OBJECT S stands for Sky and assigns the DPR TYPE header keyword to SKY The AO loop is closed for the former and open for the latter The total number of spatial offsets is defined by the parameter Number of offset positions This number can be different from the number of elements in the aforementioned lists If the number of spatial offsets is larger than the number of elements in a list the list is restarted from the beginning as many times as needed until the correct number of offsets have been done These lists can have any length however having lists of different lengths can become extremely confusing It is good practice to use lists of equal length or lists with only one value if one parameter is not changed Unlike other templates this template does not have a Return to Origin T F flag This flag refers to the spatial offsets only and the template will do this automatically before rotating the rotator to the new position Table 7 16 describes the parameters of this template Rotator offset angles are entered as a list The angles are relative so a sequence with 0 33 0
73. arameters of NACO coro obs Astro Table 7 24 parameters of NACO coro cal NigbtCalib Table 7 25 Parameters of NACO coro cal StandardStar Table 7 26 parameters of NACO sdid obs Stare Table 7 27 Parameters of NACO sam obs GenericOffset 20 91 92 94 96 97 98 99 101 103 105 105 106 107 108 NaCo User s Manual VLT MAN ESO 14200 2761 1 SCOPE This is the NaCo hereafter NaCo User Manual It can be used as a reference for users interested in preparing observing proposal with NaCo This document has been completely revised and partly rewritten in 2008 using the latest available version authored by N Ageorges and C Lidman 1 1 List of Abbreviations amp Acronyms This document employs several abbreviations and acronyms to refer concisely to an item after it has been introduced The following list is aimed to help the reader in recalling the extended meaning of each short expression IRACE Infra red Array Control Electronics 10 NaCo User s Manual VLT MAN ESO 14200 2761 11 NaCo User s Manual VLT MAN ESO 14200 2761 INTRODUCTION The Nasmyth Adaptive Optics System NAOS and the High Resolution Near IR Camera CONICA are installed at the Nasmyth B focus of UT4 NaCo provides multimode adaptive optics corrected observations in the range 1 5 um NAOS Section 4 is an Adaptive Optics AO system Section 4 1 that is designed to work with natural guide sources NGS point like0 o
74. as order sotting filters in spectroscopy 8 2 CONICA Neutral Density Filters CONICA is equipped with a short wavelength 1 to 2 5 um and a long wavelength gt 2 5 um neutral density filter The wavelength dependence of the attenuation is shown in Figure 8 2 109 NaCo User s Manual VLT MAN ESO 14200 2761 Neutral Density Filter 0 025 Transmission INT 08 1 12 1 4 16 18 2 22 24 26 28 3 32 34 36 38 4 42 44 46 48 5 52 54 56 58 6 Wavelength um Figure 8 2 Transmission curves of the CONICA neutral density filters 110 NaCo User s Manual VLT MAN ESO 14200 2761 9 PREPARATION SOFTWARE This section describes the Preparation Software PS which is a key tool in the preparation of OBs in both Visitor and Service Mode The purpose of the PS is to find the optimal NAOS configuration for a given set of conditions to compute the associated performance and to provide input to P2PP and the ETC Input to the PS is done through a Graphical User Interface GUI and includes atmospheric conditions such as seeing and airmass target parameters such as the observing wavelength and the dichroic and reference source parameters such as brightness morphology and the distance between reference and target Output consists of a configuration file for P2PP Sec B 8 an estimate of the performance in terms of Strehl a 2 dimensional PSF and an HTML formatted file Sec B 7 for the ETC The ETC can be accessed
75. ata pertaining to the selected reference object A confirmation dialog is shown to prevent mistakes o Clear all same as above except that all reference objects of the table will be erased o Duplicate makes a copy of all the characteristics of the currently selected reference object and adds it at the bottom of the list This may prove useful if you want to experiment with a reference object and you want to be able to compare different results of optimization while keeping all of them in the GUI instead of simply overwriting the results 9 5 2 Morphology The Preparation Software and the NAOS instrument can also handle moderately extended objects up to 3 arcsec in diameter to analyze the incoming wavefront Several models are available to define the morphology of the reference object Objects with one of three different morphologies can be used as NAOS reference objects o Point like object o Binary object which requires an angular separation between the two components given in the range 0 2 5 in arcsec and 114 NaCo User s Manual VLT MAN ESO 14200 2761 the flux ratio of the two components flux of fainter companion flux of brighter component dimensionless o Disc like object When using a resolved object in the solar system you are asked to enter its diameter in arcsec This morphology is modeled by a limb darkened disk 9 5 3 Photometry The PS also has to compute the flux coming from the ref
76. be T F T Data cube flag List of NDIT s NODEFAULT List of NDIT s NEXPO per offset position 1 Number of exposures per offset position Number of offset positions NODEFAULT Number of offset positions Observation type O or S NODEFAULT O is in closed loop S in open loop Offset coordinates NODEFAULT SKY or DETECTOR List of offsets in RA or X NODEFAULT Offsets in arcsec List of offsets in DEC or Y NODEFAULT Offsets in arcsec Filter NODEFAULT Filter name SAM Mask Full Name of SAM mask Camera NODEFAULT Camera Name 108 NaCo User s Manual VLT MAN ESO 14200 2761 8 FILTER TRANSMISSION CURVES 8 1 CONICA Broad Band Imaging and order sorting filters The transmission curves at the J H Ks Lp Mp and spectroscopic order sorting filters are displayed in Figure 8 1 Electronic versions of the transmission curves of all filters including the NB and IB filters are available from the NaCo web pages 1 T T T T T T T T T T T T T T T SH 0 8 N S di f II G IV bed i f N ta 0 6 x ar gt J J H Il K S S K ny A 0 4 ka oe 0 2 j 0 21 L I L AY I pA S t n 1 Lu Nome i 1 1 5 2 2 5 Wavelength microns Transmission Wavelength microns Figure 8 1 Filter curves for J H Ks Lp and Mp and the order sorting spectroscopic filters SJ SK L The SH and L band filters are also used
77. behind the mask o Removal of the ND Shott filter if used The Full_Uszd mask is inserted instead o Adjustment of DIT if needed o Fine centring behind the mask o Record the final acquisition image of the star finely centred behind the mask 84 NaCo User s Manual VLT MAN ESO 14200 2761 Table 7 6 describes the parameters of this template Table 7 6 Parameters of NACO_img_acq_SDIMoveToMask P2PP Label Default Values Description DIT NODEFAULT Detector Integration Time sec NDIT NODEFAULT Number of DITs Type of AO Observation LGS NGS NODEFAULT LGS or NGS observation type PSF Reference T F F Set to T if it is a PSF reference star Pupil Tracking Mode T F F Set to T for Pupil tracking observations RA offset arcsec 5 RA offset for sky image DEC offset arcsec 5 DEC offset for sky image Position angle on sky 0 Position angle or pupil angle in degrees Add Velocity Alpha 0 Additional tracking velocity in arcsec sec Add Velocity Delta 0 Additional tracking velocity in arcsec sec Neutral Density Filter Full_Uszd Neutral density Filter Full Uszd none BB filter wheel H Filter name H or empty NAOS Parameter file NODEFAULT NAOS aocfg file from the JNPS 7 3 7 NACO img acq Polarimetry This template does a telescope preset and is followed by interactive centering of the object It is very similar to the NACO img acq MoveToPixel template however it must be followed by a polarimetric template that uses the Wollasto
78. ber of exposures per offset position Number of offset positions NODEFAULT Number of offset positions Return to Origin T F T Return to origin at the end of the template Filter NODEFAULT Filter name Neutral Densty Filter Full Neutral density filter Full none Camera NODEFAULT Camera Name 87 NaCo User s Manual VLT MAN ESO 14200 2761 7 4 2 NACO img obs GenericOffset This template is used for imaging and has the flexibility to do any sequence of telescope offsets either in detector or sky coordinates Table 7 10 describes the parameters of this template Telescope offsets are defined as lists with the parameters List of offsets in RA or X and List of offsets in DEC or Y The offsets are relative to the previous position are in RA and DEC ot in X and Y depending on the Offset Coordinates parameter and are defined in arcsec Additionally the observation type can be defined for each image and is entered as a list in the parameter Observation Type O or S O stands for Object and assigns the DPR TYPE header keyword to OBJECT S stands for Sky and assigns the DPR TYPE header keyword to SKY The AO loop is closed for the former and open for the latter The total number of offset positions is defined in the parameter Number of offset positions This number can be different from the number of elements in the aforementioned lists Lists do not need to have the same length If the number of exposures is larger than th
79. bjectives and other dichroics will be taken when these modes are used Observations in J H and Ks will be done with the detector in Double_RdRstRd and observations in Lp and Mp will be done in Uncorr Zero points in all other filters and readout modes are not supported by the calibration plan and users should prepare the necessary OBs These calibrations aim to provide a photometric accuracy of 5 Users needing higher accuracy should provide standard stars OBs that will be executed either immediately before or after their observations The time spent doing these observations will be charged to the user o Extinction coefficients for J H and Ks filters The observatory does not measure extinction every night Instead the observatory has calculated the average extinction from data that have been taken since operations began o Twilight Flat Fields in all filters Observations in J H and Ks will be taken with the detector in Double_RdRstRd observations in Mp Lp NB 3 74 and NB 4 05 will be done in Uncorr and observations with the remaining narrow or intermediate band filters will be done in FowlerNsamp Because of the difficulty in taking twilight flats with NaCo some setups filter objective may be missed In these cases the daytime lamp flats can be used as an alternative o Lamp flats in all filters objectives and readout modes with the exception of Mp Lp NB 3 74 and NB 4 05 o Detector darks in all readout modes and DITs as required
80. ca FoV Conica FoV 1 1 x 1 1 Figure 7 1 Orientation for imaging polarimetry and coronagraphy Left Field orientation on detector at 0 rotation angle on sky Right Field orientation at 45 rotation angle on sky O For imaging polarimetry and coronagraphy Fast is on the left X of the images for zero position angle For spectroscopic acquisition East is at the top Y for zero position angle For imaging polarimetry and coronagraphy North is at the top Y of the images for a zero position angle For spectroscopic acquisition North is on the right X for a zero position angle Position angle on sky This angle is measured in the standard way i e it is positive from North to East The slits are oriented along detector rows For spectroscopy a position angle of zero means that the slit is aligned North South 78 NaCo User s Manual VLT MAN ESO 14200 2761 o For polarimetry a position angle of zero means that the mask is aligned East West Position Angle 0 deg Position Angle 45 deg 1024 1024 1024 1024 Y E Conica FoV Conica Foy N 1 1 x 1 1 X Figure 7 2 Orientation for spectroscopic observations Left Field orientation on detector at 0 rotation angle on sky Right Field orientation at 45 rotation angle on sky The templates make extensive use of telescope offsets In some templates the offsets are set automatically e g NACO img obs Autolitter but in others t
81. can be from 0 to 3 n pairs of exposures are taken Each pair consists of one exposure with the flat field lamp on and one exposure with the flat field lamp off If n is set to zero no lamp flats are taken The default is one This template should be used to take flats with the 4QPM the semi transparent coronagraphic mask and SDI 4 Only the SW filters are supported LW lamp flats are not possible For the LW filters the only alternative is to use a sky frame to flat field the data Table 7 24 describes the parameters of this template Table 7 24 Parameters of NACO_coro_cal_NightCalib P2PP Label Default Values Number of night flats 1 Description Night time flat field 7 8 4 NACO coro cal StandardStar This template is used to observe standards with the semi transparent coronagraphic mask It is similar to the NACO img obs GenericOffset template see section 6 5 3 with the difference that some DPR keywords in the FITS headers of the images are set to values that allow pipeline processing and archiving Additionally NDIT is single valued in this template and offsets are in detector coordinates only 105 NaCo User s Manual VLT MAN ESO 14200 2761 Users should specify the offsets with some care as the purpose of this template is to allow photometry with the glass plate that holds the coronagraphic mask Images of the coronagraphic masks are available from the NaCo web pages This template can also be used to observe ph
82. chnique that reduces quasi static speckle noise and facilitates the detection of early companions More work is needed to characterize the mode and to make it available to the community but it is hoped that full or partial availability will be ready in time for P82 Pupil tracking is set during acquisition of the target The users have only to specify in their template the need for pupil tracking set the flag to T and the position angle at which they wish the telescope spiders to be set Once set in the acquisition pupil tracking will be left on for the duration of the science For observations requiring a calibrator it is also possible to specify that the spiders keep the same orientation on sky as for the science In this case the PSF flag in the acquisition template for the calibrator has to be set to T Given its complexity and novelty pupil tracking is only offered in VM Interested users are encouraged to contact the Instrument Team at naco eso org for the latest information on the availability of the mode and its characteristics 60 NaCo User s Manual VLT MAN ESO 14200 2761 6 OBSERVING WITH CONICA AT THE VLT As with other ESO instruments users prepare their observations with P2PP Acquisitions observations and calibrations are coded via templates Section 7 and two or more templates make up an Observing Block OB OBs contain all the information necessary for the execution of an observing sequence Specific to NAOS
83. cience object can be smaller than the slit width which leads to the wavelength shift that depends on the location of the object in the slit o A complex line profile The spectrum is the sum of a diffraction limited core and a halo that is limited by the external seeing The result is a combination of line profiles in the final spectrum the line core is at the highest spectral resolution while the wings have a lower spectral resolution since they are defined by the slit width Calibrating AO corrected IR spectra is therefore more complicated than calibrating IR spectra from a non AO instrument The steps are similar in both cases but the accuracy at which it can be done in AO corrected spectra is likely to be lower It will be harder to remove telluric lines that come from the Earth s Atmosphere and to do spectro photometric calibration 19 NaCo User s Manual VLT MAN ESO 14200 2761 4 NAOS 4 1 Overview NAOS provides a turbulence compensated f 15 beam and a 2 arcmin FOV to CONICA Two off axis parabolas re image the telescope pupil on the deformable mirror and the Nasmyth focal plane on the entrance focal plane of CONICA A schematic sketch of the optical train of NAOS common path is shown in Figure 4 1 The optical trains of the wavefront sensors are not shown in this figure The tip tilt plane mirror TTM compensates for the overall WF tip and tilt which are the largest disturbances generated by the turbulence CONICA Input
84. closed For the sky positions the AO loop will be open Table 7 14 describes the parameters of this template 90 NaCo User s Manual VLT MAN ESO 14200 2761 By default there is no telescope offset before the first exposure If the parameter Return to Origin T F is set to true T the telescope moves back to its original position at the end of the template If not the telescope is not moved The Number of AB or BA cycles defines the number of OBJECT SKY or SKY OBJECT cycles to be executed These cycles are executed in ABBA sequences E g if Number of AB or BA cycles is set to 3 6 exposures will be taken in an ABBAAB sequence The template provides the possibility of rotating the instrument between object and sky frames so that pupil ghosts can be minimised all object frames have the same position angle on sky The technique has proved to be efficient with SOFI and ISAAC For NAOS CONICA it is not required for observations with the SW filters but it may be needed for the LW filters In addition the template provides the flexibility to adjust the number of NDIT sub integrations for the OBJECT and SKY frames NDIT for the OBJECT positions defines the number of sub integrations on the object and NDIT for the SKY positions defines the number of sub integrations on the sky The total integration time excluding overheads is defined in seconds by DIT x NDIT for the OBJECT positions NDIT for the SKY positions
85. cond box should be drawn o For spectroscopic templates the reference star used for preliminary slit centring must be identified o For PSF reference stars the OB name must be prefixed with the string PSF_ o For pre imaging the OB name must be prefixed with the string PRE_ o For PSF observations which are to be done as pre imaging the OB name must begin with PRE_PSF_ o The magnitude of the brightest object in all fields including standard stars must be explicitly given in the README file or otherwise indicated on the Finding Charts or the User Comments field of the OB 6 9 Reference sources for wavefront sensing The brighter the reference source is and the closer it is to the science target the better the correction will be It can even be the science target itself if it is sufficiently bright and point like Whenever possible several reference sources should be chosen in order to avoid acquisition problems due to binarity faintness or proper motion of the reference source The Guide Star and 2MASS catalogues can be used to find suitable references However for LGS observations to ease the development of operations the user is restricted to a single Tip Tilt Star per LGS OB at least for P82 In general the visual WFS will be used as this ensures that the largest fraction of IR light enters the science channel The IR WFS should be used for very red sources V K 2 6 mag which could otherwise not be observed with NA
86. condary mirror are not depicted here but they have an important effect which will be discussed later 0 lt 2 O O5 O Oo KN com oO KG Figure 5 14 Optical diagrams showing the effect of apodizing the pupil with the four 2 dimensional masks implemented in the CONICA camera 5 6 1 SAM why and when to use it Masking is useful for very narrow fields of view the outer limit is set by the resolution of the shortest baseline in the mask Any advantages it enjoys over conventional full pupil imaging are only manifest at such very high resolutions typically within several resolution elements of the PSF core In the infrared this typically means that the scientific niche is for objects where the entire field of interest lies within several hundred milli arcsec from a bright star Although there may be ways to mosaic larger fields together these have never been successfully demonstrated Key strengths of a dilute and ideally non redundant pupil are in the mitigation of atmospheric phase noise seeing and the use of robust self calibrating observables such as the Closure Phase For brevity we refer the reader to the references section for discussion of the philosophical underpinnings which motivate masking interferometry Masking is furthermore by its nature limited to brighter classes of targets This is because it is only effective at combating atmospheric phase noise seeing and it is counterproductive in photon starved reg
87. coordinates of the reference which sets the distance to target Oo the reference brightness and o the reference morphology If the reference object is the target one can use the Target gt Reference Object option from the Objects menu at the top of the panel as a shortcut For test purposes the interface can be run without knowing the precise coordinates of the target nor the reference object In this case one need only enter the separation between the two But names and coordinates must be supplied if the interface is being used for OB preparation The default morphology of the reference object is point like which does not need any additional input Other morphologies can be specified Other buttons that can be seen next to Register Object are o Reset Form this simply erases the form without confirmation o Update Object if you are modifying the characteristics of a reference object which is already recorded in the table this button will automatically turn red reminding you to click this button to record your changes o Cancel cancel any changes to the selected reference Underneath the table is another set of buttons which allows one to manipulate the list of reference objects o Up Down moves the selected object in the list by swapping it with its neighbor The order in which the reference objects are shown will be the one exported to P2PP Sec B 8 and hence the one tried at the telescope o Delete this discards all d
88. crowded fields NACO img obs AutolJitter Imaging of extended objects or crowded fields NACO img obs GenericOffset NACO im g ob s_FixedSkyOffset or Imaging requiring special offset sequences NACO img obs GenericOffset Imaging with chopping in Lp or Mp NACO img obs AutoChopNod Imaging with SDI NACO sdi obs GenericOffset Spectroscopy Spectroscopy of point like or moderately extended objects NACO spec obs AutoNodOnSlit Spectroscopy of extended objects complex sequences of positions gt 10 or NACO spec obs GenericOffset Polarimetry Imaging Polarimetry NACO pol obs GenericOffset Polarimetry with the Half Wave Plate NACO pol obs Retarder Coronagraphy Coronagraphy NACO cofro obs Stare Coronagraphy imaging NACO coro obs Astro SDI 4 4QPM H cotonagtaphy SDI NACO sdi4 obs Stare SAM SAM includes Pupil Tracking observations NACO sam obs GenericOffset Standard Stars Standard star for imaging Standard star for imaging with chopping Standard star for coronagraphy Standard star for spectroscopy Standard star for polarimetry NACO img cal StandardStar NACO img cal ChopStandardStar NACO cofro cal StandardStar NACO spec cal StandardStar NACO pol cal StandardStar Night time calibrations Night time coronagraphic and SDI 4 flats NACO coro cal NightCalib Night time spectroscopic flats and arcs
89. d or FowlerNsamp For observations with LW filters the readout mode should be set to Uncott All imaging templates make use of the NEXPO per offset position parameter It is the number of exposures one exposure DIT x NDIT per offset position For very bright targets see Sec 5 15 a neutral density filter can be inserted into the light path The choices are Full for no neutral density filter ND_Long for a LW neutral density filter and ND Shott for a SW neutral density filter For LW observations without chopping only the NACO_img_obs_AutoJitter template should be used The sky subtraction with the other templates is generally unsatisfactory 7 4 1 NACO img obs Autolitter This template offsets the telescope between exposures according to a random pattern of offsets automatically determined by the template It is ideal for long integrations on sparse fields and does not require a long list of offsets to be defined The offsets are distributed randomly within a box whose size is defined by the parameter Jitter Box Width in arc seconds with the condition that the distance between any two points in a seties of ten values is greater than a system determined minimum This is intentionally done to ensure that the 5 frames before and after any frame are spatially not too close and can be safely used for creating skies without residual objects for sky subtraction 86 NaCo User s Manual VLT MAN ESO 14200 2761 1024 1024 N
90. d usg http www eso org observing dfo quality index_naco html For any question regarding NaCo Service Mode operations the point of contact is the User Support Department usd help eso org in Garching Users with approved Visitor Mode programs VM can contact naco eso org 2 2 Current version of the manual This is version 82 1 of the NaCo User Manual applicable for phase II preparation for P82 Since NaCo is in constant improvement and modes are refined especially the new ones it is advisable to check the NaCo web page for possible updates to this manual and for recent news 2 3 Changes for P82 The following changes are implemented for P82 SAM Tentatively offered pending commissioning sparse aperture mask interferometry uses special aperture masks in the pupil wheel to obtain the very highest angular resolution at the diffraction limit When used correctly these masks transform the single 8 m telescope pupil into a sparse interferometer array and it is therefore necessary to understand the principles of optical interferometry and in particular the recovery of complex Fourier data amplitudes and phases from the Fizeau interference patterns that result SAM is offered in VM only Cube mode Tentatively offered pending commissioning this mode is a variant of the of the burst mode already offered with VISIR and ISAAC In this mode a data cube with each single DIT frame is saved This mode is particularly interesting f
91. des of the array as well as the bias level of rows 512 amp 512 disappear in the background subtraction 5 7 2 DIT and NDIT The IRACE controller controls the detector front end electronics and manages pre processing of the data before transferring them to the workstation A single integration corresponds to DIT Detector Integration Time seconds The pre processor averages NDIT of these before transferring the result to disk Note that the number of counts in the images always corresponds to DIT not to the total integration time i e DIT x NDIT 5 7 3 Readout Modes and Detector Modes The readout mode tefers to the way the array is read out We offer three readout modes o Uncorr The array is reset and then read once It is used for situations when the background is high e g LW imaging The minimum DIT without windowing is 0 1750 seconds For observations in Mp the array is windowed to 512x514 and the minimum DIT is 0 0558 seconds o Double RdRstRd The array is read reset and read again It is used for situations when the background is intermediate between high and low Eg SW imaging or LW spectroscopy The minimum DIT is 0 3454 seconds o FowlerNsamp The array is reset read four times at the beginning of the integration ramp and four times again at the end of the integration ramp Each time a pixel is addressed it is read four times It is used for situations when the background is low Eg SW spectroscopy or SW NB imag
92. dth should be smaller than the throw o Cube mode is a feature that can be turned on for science templates not acquisition by means of the flag in the P2PP file Note that the default window is 1024x1026 and other windows will have different sizes 512 256 128 and 64 with NY NX 2 centred on pixel 512 512 i e the user cannot set STARTX and STARTY the lower left coordinates for the detector window o Pupil tracking mode is set in the acquisition template by means of the correspondent flag in P2PP Note that all the acquisition templates including the ones for modes that are not offered with pupil tracking contain this flag 76 NaCo User s Manual VLT MAN ESO 14200 2761 Table 7 1 NaCo template suite Action Template General to all observing modes Turn the field telescope rotator NACO all obs Rotate Acquisition Templates Preset telescope and acquire for imaging NACO_img_acq_MoveToPixel Preset telescope and acquire for SDI NACO_im g_acq_SDIMoveToPixel Preset telescope and acquire for polarimetry NACO img acq Polarimetry Preset telescope and centre object s in the slit NaCo img acq MoveToSlit Preset telescope and centre object behind a mask NACO im g acq MoveToMask Preset telescope and centre object in SDI 4 NACO img acq SDIMoveToMask Preset telescope and acquire for SAM NACO_img_acq_SAMMoveToPixel Imaging or SDI Imaging of un
93. e nodding frequency is also automatically defined in the templates DIT and NDIT are not parameters of the LW chopping templates as they are automatically set to the optimal values imposed by the chopping frequency and saturation levels Chopping with NaCo differs from chopping with ISAAC in one fundamental aspect In order for the loop to be closed for both the ON and OFF beams the FS in NAOS must move in phase with M2 This technique is called counter chopping It is strongly advised not to attempt chopping for fields where the AO reference star does not allow to correct with a frequency of at least 100Hz 6 6 Target acquisition 6 6 1 Imaging The NACO img acq MoveToPixel template provides interactive tools like dragging arrows to define telescope offsets For SDI users must use template NACO_acq_img SDIMoveToPixel 63 NaCo User s Manual VLT MAN ESO 14200 2761 6 6 2 Spectroscopy It is mandatory to use the NACO img acq MoveToSlit acquisition template for all spectroscopic OBs and the same slit in both the acquisition and observing templates This template provides interactive tools to rotate the field and to centre objects into the selected slit that is overlaid on the Real Time Display RTD It can also be used to place two objects in the slit without having to pre compute the position angle Instructions for specifying this acquisition procedure at phase II are in Section 7 3 4 These instructions must be strictly
94. e fit is valid from 1 to 4 microns 3 Fit based on telluric absorption features at 5 microns The fit is valid from 4 5 to 5 5 microns 42 NaCo User s Manual VLT MAN ESO 14200 2761 5 4 4 5 4 5 that was used for the science target The stars are generally chosen from the Hipparcos catalog and are either hot stars spectral type B9 or earlier or solar type stars spectral types GOV to G4V These calibrations are taken so that telluric features can be removed from science spectra At this point in time we cannot say how accurate these calibrations will be Should users wish to use telluric standards of a particular spectral type they should provide the corresponding OBs and detailed instructions In this case the time for executing the OBs will be charged to the user and the observatory will not observe a separate telluric standard Spectroscopic lamp flats in all SW spectroscopic modes slits and readout modes Spectroscopic arcs in all spectroscopic modes and slits An atlas of lines for the SW modes is available from the NAOS CONICA web page LW spectroscopic arcs are not supported For slitless spectroscopy arcs with the 86 mas slit will be provided Detector darks Darks are taken at the end of each night with the DITs and readout modes used during the night Special notes about the prism calibration For the L27_P1 mode given the low resolution at 1 micron and the high background at 5 microns the normally used telluric
95. e most promising way to overcome the isoplanatic angle limitation is the use of artificial reference stars or laser guide stars LGS Laser Guide Stars are artificial sources potentially replacing Natural Guide Stars NGS as reference objects for Adaptive Optics AO image corrections The rationale is the much higher sky coverage offered in principle by an LGS as opposed to the standard NGS approach Due to the bright V 11 13 artificial star created near the centre of the field the probability to achieve a given minimum AO correction on an arbitrary astronomical target goes e g from a meagre 3 with an NGS to 65 with an LGS for corrected images with at least a 20 K band Strehl ratio Nevertheless there are still a number of physical limitations with an LGS The first problem is the focus anisoplanatism also called the cone effect Because the artificial star is created at a relatively low altitude back scattered light collected by the telescope forms a conical beam which does not cross exactly the same turbulence layer areas as the light coming from the distant astronomical source This leads to a phase estimation error The effect is roughly equivalent on an 8 m telescope to the phase error experienced with an NGS 10 away from the astronomical target However contrary to the case of NGS only AO LGS based corrections saturate at a relatively low maximum K band Strehl ratio of 55 due to the cone effect Even mote severe is the image
96. e number of elements in a list the list is restarted from the beginning as many times as needed until the correct number of frames have been acquired The lists can have any length however having lists of different lengths can become extremely confusing It is good practice to use lists of equal length or lists with only one value if one parameter is not changed At the end of the template the telescope is returned to the original position if the parameter Return to Origin T F is set to true T If not the telescope is not moved at the end of the template Figs 20 and 21 illustrate how this template can be used The total integration time is defined in seconds by DTD ee es NDIT x NEXPO per offset position Table 7 10 Parameters of NACO_img_obs_GenericOffset P2PP Label Default Values Description DIT NODEFAULT Detector Integration Time sec Readout mode Double_RdRstRd Readout mode Window Size 1024 Size of the window Observation Category SCIENCE Observation Category Store Data Cube T F F Data cube flag List of NDITs NODEFAULT List of NDITs NEXPO per offset position 1 Number of exposures per offset position Number of offset positions NODEFAULT Number of offset positions Observation type O or S NODEFAULT O is in closed loop S in open loop Offset coordinates NODEFAULT SKY or DETECTOR List of offsets in RA or X NODEFAULT Offsets in arcsec List of offsets in DEC or Y NODEFAULT Offsets in arcsec Filter NODE
97. e of the nod is defined by the Nod throw parameter The first exposure A is taken after offsetting the object along the slit by Nodthrow arcsec The second exposure B is therefore NodThrow 2 from the initial position along the slit In addition to nodding random offsets can be added in the middle of a cycle A sequence of 6 cycles with jittering will result in the following sequence A E G E A E A E B E B E A E A E B E B E A E where E are random offsets In order to avoid the possibility of overlapping spectra E should be smaller than half of the nod throw The random offsets are generated inside an interval defined by the parameter Jitter Box Width in arcseconds Offsets are randomly distributed between JitterBoxWidth and JitterBoxWidth It is strongly recommended to define some non zero value for the Jitter Box Width parameter as 94 NaCo User s Manual VLT MAN ESO 14200 2761 this allows one to get several images with the spectra lying at different positions on the detector However it should be smaller than the Nod throw otherwise spectra on either side of the throw could overlap 1024 1024 y Acquisition Position Jitter Box 6 23 14 5 Nod Throw Slit Angle 0 degrees N CONICA FOV S27 28 1 1 X Figure 7 7 An illustration of how the NaCo spec obs AutoNodOnSlit template works with Jitter Box Width 5 Return to Origin T Number of AB or BA cycles 3 NEXPO per o
98. e signals which may be weak or zero everywhere and thus lead to difficulties in producing a good image The following sections report on sky results obtained during commissioning They are taken directly from the report of P Tuthill PI of SAM School of Physics Sydney University NSW 2006 AUSTRALIA and S Lacour Co I CNRS Grenoble France 5 6 9 On sky observations VY Canis Majoris VY Canis Majoris is a bright M supergiant which has produced an extensive infrared nebula several arcsec in extent At the core VY CMa exhibits a bright asymmetric plume first imaged in detail in Monnier et al 1999 ApJ 512 351 This form of strongly asymmetric structure together with the spatial structure on ideal scales of less than 200 milli arcsec all makes VY CMa an ideal test target for SAM commissioning at CONICA Figure 5 15 below shows images produced in narrowband filters within the H and K bands using 18Holes mask data recorded at the CONICA commissioning run in March 2008 There is some correspondence between the AO only and masking images in that there is evidence for a similarly skewed center of brightness in the AO image However the fine detail and diffraction limited structures appearing in the masking data cannot be seen in the AO image It is possible that with deconvolution using a carefully recorded PSF frame that more real structure may be recovered from the AO but this procedure has proved to be controversial in the past and can l
99. e the slit position in a crowded field 2 imaging templates only NACO_img_obs_AutofJitter and NACO_img_obs_GenericOffset For these 2 templates a new user selectable keyword Observation Category has been introduced and should be set to PRE IMAGE in the above mentioned cases only By default this parameter is set to SCIENCE Failure set this keyword properly will result in delays to process and deliver the pre imaging data 6 8 Finding charts readme files and OB naming conventions In addition to the general instructions on finding charts and README files that are available at 64 NaCo User s Manual VLT MAN ESO 14200 2761 http www eso org observing p2pp ServiceMode html the following NaCo requirements apply o At least one chart for each observation must be 2 x 2 in size with additional charts showing more detail as appropriate o All wavefront reference stars must be clearly marked according to the way they are otdered in the preparation software They should be marked R1 R2 R3 etc o For imaging the field of view of the selected camera must be drawn o For polarimetric and coronagraphic observations the field of view of the selected camera must be drawn and the object that is to be placed behind the mask in the case of coronagtaphy or centred in the mask in the case of polarimetry should be clearly indicated o For long slit spectroscopy the slit must be drawn o For slitless spectroscopy a 14 x 14 arcse
100. e the Wollaston 45 mask had to be removed to make space for the 4QPM in H and K the coronagraphic masks and the slits for spectroscopy The Fabry Perot wheel which is set to open for non FPI observations The Lyot wheel which includes the ND filters The grism wheel which contains the grisms the prism the SDI not in use anymore and SDI Wollastons the wire grid analyzers for polarimetry not in use anymore and the J broadband filter The first filter wheel which contains all the intermediate band IB filters NB 2 17 NB 2 12 and NB 4 05 The second filter wheel which contains all the broad band filters except J the remaining NB filters and the order sorting filters used in spectroscopy The camera wheel which contains all the objectives 24 NaCo User s Manual VLT MAN ESO 14200 2761 Adapter Callbratlon Source a o Gr Cryogenlc Shutter Aa J NE T Mask Wheel Colllmator Fabry Perot Pupll Stop Closed Cycle Cooler Detector TTLN2 Cyellng Radlatlon Shleld Figure 5 1 CONICA Schematic overview 5 1 Imaging Imaging and SDI Simultaneous Differential Imaging uses different combinations of filters and cameras 25 NaCo User s Manual VLT MAN ESO 14200 2761 5 1 1 Cameras The characteristics of the cameras of CONICA are described in Table 5 1 in terms of plate scale and field of view Each camera has a corresponding field mask which is automatically set by the i
101. ea of the performance contrasts as high as 30 000 between a bright H lt 7 mag primary stat and methane rich object T 4 lt 1000 K can be obtained in 40 min with a signal to noise ratio of 6 Figure 5 2 Flat field image of the SDI mode The transmitted wavelengths are 1 6 um top left 1 575 um top right and 1 625 um bottom left and right 5 17 SDI On sky performance Figure 5 3 shows the contrast curves 5 sigma obtained from the reduced SDI images of AB Dor In particular this is for the first two roll angles of saturated data DIT 5s 17 min total exposure time We re attaining 5 sigma contrasts of Delta F1 1 575 um 10 mag at 0 5 and Delta F1 1 575 um 11 mag at 1 which is comparable if not slightly better to the performance of the old SDI device on the same star shown in Figure 5 4 It is important to note that the contrast curve provided for the old device was with a longer exposure time 28 minutes so SDI probably can attain a somewhat better contrast than SDI given the same exposure time For comparison Figure 5 4 also shows contrast curves for a variety of survey stars including AB Dor observed with the old SDI device The fact that the SDI curve seems to bottom out to a nearly constant value around 2 suggests that the contrast is readnoise limited for radius gt 2 29 NaCo User s Manual VLT MAN ESO 14200 2761 CONICA PSF Or EE Optimized Conventional AO SDI AF
102. ead to spurious structures TTTTTTTTITTTTTTTTTITTTTTTETTTTTTTTT FT ER 100 p E o GO S On 100 E x 2 24um vd a a FANE Aa ee Ce ST Ee RT EEE T TO Gd Vs TO a ET TONY TOEN PONE OO TE Wat CoH OT Ct CY ep 100 0 100 100 0 100 Milliarcseconds Milliarcseconds 50 NaCo User s Manual VLT MAN ESO 14200 2761 Figure 5 15 Canis Majoris images reconstructed from 18 hole masking data 5 6 10 Faint companion detection Dynamic ranges obtained within this realm have been demonstrated to be in excess of 200 1 for point source detections To attain this level of precision careful analysis of closure phase signals is required and exhaustive understanding of error sources such as PSF calibration and chromatic effects arising from atmospheric dispersion Furthermore with full recovery of closure phase signals complex and arbitrary flux distributions can be mapped with high fidelity The particular strengths of aperture masking are for relatively bright targets where there is resolved or partially resolved structure within a few resolution elements of bright PSF cores 5 6 11 On sky observations AB Dor in H and K 400 i i f f i T T T T T T Tal 141 l 200 n y F 5 oO E ok re oO K 200 y t 129 400 1 1 1 1 1 1 1 1 1 it 1 1 1 400 200 0 200 400 400 200 dec mas fan 200 400 400 200 0 200 400 RA
103. ed in a dedicated laboratory under the Nasmyth platform of UT4 Figure 4 2 A custom made single mode fibre carries the high laser power to the 50 cm launch telescope situated on top of the secondary mirror assembly providing the best possible artificial source image quality As a safety measure a twin whole sky camera with specialized software is used to monitor incoming aircraft and shut down the laser beam when an airplane enters field of view of the telescope Figure 4 2 Illustration of the LGSF set up at UT4 the laser clean room is installed below Nasmyth A note that NaCo itself is installed at Nasmyth B The laser beam is propagated via fibre to the launch telescope installed at the back of M2 23 NaCo User s Manual VLT MAN ESO 14200 2761 5 CONICA CONICA is an IR 1 5 um imager and spectrograph which is fed by NAOS It is capable of imaging including Simultaneous Differential Imaging long slit spectroscopy coronagraphy polarimetry and Sparse Aperture Masking observations with several different plate scales This section describes the optical components of CONICA See Figure 5 1 for a drawing of the instrument The optical path includes the following components O The slider wheel which is either open closed in calibration position or with the Half Wave Plate inserted The mask slit wheel which contains various masks for imaging SDI and polarimetry note that now only the Wollaston 00 is available sinc
104. eference subtraction is only done on 3 4th of the data 8 images out of 11 to match the parallactic angle of the star and its reference In Figure 5 12 the SDI processing solid green appears to be slightly better for the short angular separation less than 0 4 than the coronagraphic imaging using subtraction of a reference star dotted black To see the effect of the rotation we added the different images we recorded after correcting for the instrument rotation in order to add up companion signal while averaging out speckle and readout noise The effect is clearly an improvement of the detection capability especially at large angular distances dashed green The subtraction of the SDI image of the star with the SDI image of the reference star solid red was also investigated This technique is more efficient than the SDI image at angular distance shorter than 1 and is the same further away Roll averaging improves also the detection capability of the instrument dashed red The standard SDI processing that consists in 2 observations at 2 roll angles separated by 33 is also given in blue but for 25 apart This results in a small improvement with respect to SDI green line Another technique which is called double roll subtraction has been tested dashed blue It consists in using only SDI data of the star and subtracting the SDI star data to themselves but with different angular separations For example we calculate the images
105. eing on reference abject D39 arcsec Aimass 1 2 7 rO on reference abject 1 11 m Thetan on reference abject 143 aresee Name TestSourceRaference Distance to Target 1347 arcsec AA Gr 02 pe Prop Mot RA 0 0 aresecyear pec 33 27 fra Prop Mot DEC D0 aresecyear Resutting Performance WW i Sr an reference abject Sie Effective sreing used 0 929 aresee at 0 5 um Tracking Tatte Sr 2 166 on ref object 20 2 gt ae Morphology Pointdike Photometry Mag Spectral Type Sr antarget 14 5 Obsenmd Magnitude 143 Band Y PAHA on reference object 0092 arcses ELS Spectral Type Fav 7 Ag fa Transmission 547 gt PSF AO conny Reset farm Register Object Update Object Cancel Export to NACO ETC Export to P2PP Figure 9 1 PS GUI 9 3 Target and Instrument Setup The observing wavelength in um can be entered as a filter in which case the wavelength automatically appears or it can be entered directly by selecting free from the list of CONICA filters and then typing the value directly into the space provided The dichroic name can be selected or left free If left free the PS will select the dichroic which maximizes the Strehl which usually means that most of the light will be sent to NAOS If another dichroic is preferable then the dichroic can be selected here Table 4 1 gives the conditions under which the various dichroics should be used Users shou
106. erence object Since the WFS spectral bandwidths are very large a single magnitude is not sufficient to compute the detected number of photons The photometric information may be provided in different ways o Magnitude Spectral Type Well suited to main sequence stellar objects If you choose this option you will need to enter the apparent magnitude the filter in which the magnitude is measured either V J H K Lp or Mp and a spectral type The spectral type is chosen in an option button The list of available values is the same as that available in the interface of the CONICA ETC This ensures the compatibility between the two tools especially in the case when the target is also used as the reference object see also section B 7 o Magnitude Temperature The magnitude is given in the same way as above value filter but in this case the spectral energy distribution is modeled as a black body which requires a temperature Moreover the users now have the possibility to provide a visible extinction Ay value by default and if not specified this value is 0 and the PS behaves exactly as before When Ay is defined it governs by how much the brightness of the AO reference target changes as function of the wavelength which is especially important due to the broad bandwidth of the wavefront sensor detectors We adopted a standard extinction law represented in Figure 9 2 as defined by Cardelli Clayton amp Mathis AJ 345 245 1989
107. error sources such as PSF calibration and chromatic effects arising from atmospheric dispersion Furthermore with full recovery of closure phase signals complex and arbitrary flux distributions can be mapped with high fidelity The particular strengths of aperture masking are for relatively bright targets where there is resolved or partially resolved structure within a few resolution elements of bright PSF cores The range of masks installed in the camera is intended to span a variety of target fluxes with the 18 holes mask being tailored to give the best results for bright targets through to the 7 holes which is for use on the faintest targets Section 8 3 below gives calibrations of the counts expected for varying mask filter combinations 5 6 16 Calibration plan for Sam Twilight flats as described in section 5 1 3 and internal flats without the masks e Detector darks in all readout modes and DITs 5 6 17 Pipeline for SAM SAM is not supported by the pipeline 56 NaCo User s Manual VLT MAN ESO 14200 2761 5 7 CONICA detector 5 7 1 General characteristics The CONICA detector is a Santa Barbara Research Center SBRC InSb Aladdin 3 array It was installed into CONICA during May 2004 and it replaces the Aladdin 2 detector that had been used since the instrument was first offered The main characteristics of the Aladdin 3 array are summarized in Table 5 10 Table 5 10 CONICA detector characteristics Detector Forma
108. ers who need calibrations beyond the ones provided by the Calibration Plan of this mode The differences with NACO_spec_obs_AutoNodOnSlit are that some DPR keywords in the FTTS headers of the images are set to different values allowing pipeline processing and archiving 7 64 NACO spec cal NightCalib This template is used for taking nighttime arcs and flat fields and it should be placed immediately after the spectroscopic templates If Night Arc T F is set to T a pair of exposures one with the arc lamp on and another with the arc lamp off will be taken If set to F no arcs are taken If Number of Night Flats is set n where n can be from 0 to 3 n pairs of exposures are taken Each pair consists of one exposure with the flat field lamp on and one exposure with the flat field lamp off If n is set to zero the default no lamp flats are taken Table 7 19 describes the parameters of this template Table 7 19 Parameters of NACO_spec_cal_NightCalib P2PP Label Default Values Description Night are T F F Night time arc Number of night flats 0 Number of flat field on off paits 7 7 NaCo polarimetry science templates These templates are for polarimetric observations with the Wollaston prism For SW observations the readout mode of the detector should be set to either Double_RdRstRd ot FowlerNsamp For LW observations the readout mode should be set to Uncorr All other combinations will be rejected at the time the OBs are checked
109. es is defined by the DIT and NDIT parameters 81 NaCo User s Manual VLT MAN ESO 14200 2761 This template records a flat on and a flat off images which can be used for flat fielding the subsequent science frames two optional reference images star and sky used by the operator to classify the OB and the final acquisition image with the star centred in the SDI field of view Table 7 3 describes the parameters of this template Table 7 3 Parameters of NACO img acg SDIMoveToPixel P2PP Label Default Values Description DIT NODEFAULT Detector Integration Time sec NDIT NODEFAULT Number of DITs Type of AO Observation LGS NGS NODEFAULT LGS or NGS observation type PSF Reference T F F Set to T if it is a PSF reference star Pupil Tracking Mode T F F Set to true for PT observations RA offset arcsec 5 RA offset for sky image DEC offset arcsec 5 DEC offset for sky image Position angle on sky 0 Position angle or pupil angle in degrees Add Velocity Alpha 0 Additional tracking velocity in arcsec sec Add Velocity Delta 0 Additional tracking velocity in arcsec sec Neutral Density Filter Full Neutral density Filter Full none NAOS parameter file NODEFAULT NAOS aocfg file from JNPS 7 3 4 NACO img acq MoveToSlit This template does a telescope preset and is followed by interactive centring of the object in the slit It is very similar to the NACO_img_acq_MoveToPixel 7 3 2 template however it must be followed by a spect
110. escope offsets It is essentially intended for programs requiring large offsets off the slit or slit scanning across one object Table 7 18 describes the parameters of this template Telescope offsets are defined as lists with the List of offsets in RA or X and List of offsets in DEC or Y parameters Telescope offsets are relative defined either along detector lines X and columns Y or RA and DEC and are in arcsec Offsets in X are along the slit offsets in Y are perpendicular to the slit Additionally the observation type can be defined for each image and is entered as a list in the parameter Observation Type O or S O stands for Object and assigns the DPR TYPE header keyword to OBJECT S stands for Sky and assigns the DPR TYPE header keyword to SKY The loop is closed for the former and open for the latter With large combined offsets the guide probe may not be able to follow the same guide star In such a case the guiding system will automatically find another star but not resume guiding A pop up window will instruct the operator to resume guiding If the guide star has changed during an offset the accuracy of the offset will be poorer than it would have been if the same guide star had been used This will only occur when offsetting from object to sky On the return offset the loop will close and the field selector in NAOS will make sure that the object remains centred in the slit even though the guide star has c
111. ever having lists of different lengths can become extremely confusing It is good practice to use lists of equal length or lists with only one value if one parameter is not changed The total number of exposures is given by NEXPO per offset pos x number of half wave plate angle x Number of offset pos Unlike other templates this template does not have a Return to Origin T F flag By default at the end of the template the telescope returns at the original position It is important to remember that for technical reasons the HWP is moved into the beam and set to its zero position at the beginning of the template and then it is moved out of the beam at the end of the template This introduces an extra 1 minute overhead per template Table 7 21 describes the parameters of this template The template can be restarted with another orientation on the sky for another series of exposures At least two different half wave plate orientations separated by 22 5 degrees are required for computing the Stokes parameters By definition a rotation of the polarisation plane by 45 degrees does correspond to a rotation of the half wave plate by 22 5 degrees To image the entire field of view while observing with the Wollaston prism the same care must be taken as for observation with the NACO_pol_obs_GenericOffset template see 6 8 2 The total integration time excluding overheads is defined in seconds by DIT x NDIT x NEXPO per offset pos x numbe
112. f the template works identically to NACO coro obs Stare The number of exposures at the object position is defined by the Number of Exposures Object Only parameter The telescope does not offset between these exposutes The number of exposures at the sky position is defined by the Number of offset positions Sky only and the telescope can offset between these exposures The sky positions are randomly distributed around a position that is set at a constant distance defined by the parameters Sky offset in DEC and Sky offset in RA from the original telescope position and within a box whose dimensions are set by the parameter Jitter Box Width in arcsec It is strongly recommended especially for very bright sources to select an area so that the main target is out of the field of view for sky measurements to avoid saturation effects The coronagraphic mask is left in the beam for the sky exposures The object positions will be observed with the AO loop closed The sky positions will be observed with the AO loop open Table 7 26 describes the parameters of this template 106 NaCo User s Manual VLT MAN ESO 14200 2761 The template provides the flexibility to adjust the number of NDIT sub integrations for the OBJECT and SKY frames NDIT for the OBJECT positions defines the number of sub integrations on the object and NDIT for the SKY positions defines the number of sub integrations on the sky The t
113. false signals Taking a second or even third visit to an important target helps to eliminate these problems 5 6 8 Imaging tests For the imaging tests given here the 18Holes mask was used This gives the best Fourier coverage and well sampled short and long baseline data This means it is well suited to imaging of 49 NaCo User s Manual VLT MAN ESO 14200 2761 complex targets but of course this mask is the least sensitive and so only relatively bright targets are shown here Imaging using the 9Holes or other masks may be possible but the more limited Fourier coverage will limit the complexity of targets that can be mapped well One way to help circumvent this problem a little would be to observe the object over a period of several hours with visits alternating between the source and calibrator This would help build Fourier coverage by Earth rotation synthesis In general errors on the visibilities produced by masking are large The Fourier amplitude data is therefore quite poor A large fraction of the success of the images depicted in this section is due to the relatively good Closure Phase data This is an important point to keep in mind because many targets that one might wish to image do not show large closure phase signals at all Closure phases arise in situations where the source has non point symmettic structure and so objects such as a spherical shell and elliptical ring or an equal binary star will all give closure phas
114. ffset position 1 Nod throw 15 To better exploit the jittering facility offered by this template it is also recommended to define the Number of AB or BA cycles to some value higher than 1 e g 4 or 5 so as to get several AB pairs of images with the spectra lying at different positions across the array If the parameter Jitter Box Width is set to zero then the template will just nod between A and B Ifthe parameter Return to Origin T F is set to true T the telescope returns to the starting position If not the telescope is not moved The NEXPO per offset position parameter defines the number of frames stored per A or B position If for example DIT 120s NDIT 1 NEXPO per offset position 8 8 images will be stored for each position If in addition the Number of AB or BA cycles is set to 2 the template will deliver in total 32 images 8 for the first A position 16 for the B position and 8 for the second A position The total integration time excluding overheads is 64 minutes Note in the case where there are several OBs using this template on the same target for several hours of integration on the same target it is recommended to modify the Nod throw parameter by a few arcsec between each OB This is for the following reason the acquisition is always done at the same position on the array i e centre of the slit Therefore different executions of the same template will position the targets at the same posit
115. for IR WES with FowlerNsamp Template parameters Acquisition Template NACO img acq MoveToPixel Observation Template NACO img obs Autolitter DIT 3 sec NDIT 20 Number of offset positions 60 NEXPO per offset position 1 Readout Mode FowlerNsamp Execution Time min Preset 3 Guide Star Acquisition 0 75 Initial Setup 2 AO Acquisition 10 Imaging acquisition 0 5 Sub Total acquisition 16 25 Observation 60x 27 20x 3 2 127 Total min 145 Overhaeds 141 Observation Number of offset positionsx Offset overhead NDITx DIT readout overhead Table 6 7 Example 2 Imaging a bright source V 11 with the VIS WES or K 7 with the IR WFS with Double_RdRstRd Template parameters Acquisition Template NACO_img_acq_MoveToPixel Observation Template NACO_img_obs_AutoJitter DIT 2 sec NDIT 30 Number of offset positions 20 NEXPO per offset position 3 Readout Mode Double R dRstRd Execution Time min Preset 3 Guide Star Acquisition 0 75 Initial Setup 2 AO Acquisition 5 Imaging acquisition 0 5 Sub Total acquisition 11 25 Obsetvation 20x 27 2x16 3x 30x2 0 7 80 3 Total min 91 6 Overheads 53 Observation Number of offset positions Offset overhead NEXPO per offset position 1 time between frames without offset NEXPO per offset positionx DITxNDIT readout overhead 71 NaCo User
116. for observations in NGS and work alternatively with each of them The list of reference objects is shown as a table at the top of the form containing all the data pertaining to the reference object Each row corresponds to a reference object showing its name if it has been provided and its angular distance to the science target mandatory parameter The other columns are filled when requesting an optimization by the PS server section B 6 If several reference objects are available in the table you can select the one you want to work with by simply clicking on the corresponding row This will update the contents of the form below the table as well as the Resulting Performance sub panel shown on the bottom left of the GUI Indeed each reference object is attached to its own configuration of the AO system and to the performance estimated when considering this configuration The order is important if the first reference object is acquired successfully then the other reference objects will not even be considered Reference objects should be sorted in decreasing ordet of expected performance Use the list manipulation buttons Up Down to modify this order as needed 113 NaCo User s Manual VLT MAN ESO 14200 2761 Every time you want to add an object to the list you must first fill in the mandatory fields and then click the button labeled Register Object at the bottom of the reference object form The mandatory fields are o the
117. for the 9 Holes mask Figure 5 20 Same as Figure 5 18 but for the BB 9 Holes mask 55 NaCo User s Manual VLT MAN ESO 14200 2761 Figure 5 21 Same as Figure 5 18 but for the 7 Holes mask 5 6 15 References and further readings We have tried to give brief notes on the practical use of the aperture masks in the CONICA camera When used correctly these masks transform the single 8 m telescope pupil into a sparse interferometer array and it is therefore necessary to understand the principles of optical interferometry and in particular the recovery of complex Fourier data amplitudes and phases from the Fizeau interference patterns that result A full explanation of the mathematical techniques necessary to do this task is beyond the scope of the present document The reader is advised to consult sources form the open literature concerning aperture masking Some useful references specific to masking include Tuthill P G et al Michelson Interferometry with the KeckI telescope PASP 112 555 2006 Tuthill P G et al Sparse aperture adaptive optics SPIE 6272 103 2006 Lloyd J P et al Detection of the Brown Dwarf GJ 802B with Adaptive Optics Masking Interferometry Ap 650 131 2006 Dynamic ranges obtained within this realm have been demonstrated to be in excess of 200 1 for point source detections To attain this level of precision careful analysis of closure phase signals is required and exhaustive understanding of
118. gure 5 5 e 4QPM_H optimized for a wavelength of 1 60 um circular field of view 8 diameter e 4QPM_K optimized for a wavelength of 2 18 um circular field of view 13 diameter These devices work best for filters that are centred at or near these wavelengths 31 NaCo User s Manual VLT MAN ESO 14200 2761 Figure 5 5 Flat field images of the 4QPM_K Ks filter left and of the 4QPM_H H filter right The many dust particles observed in the flats generate flat field variations of 10 20 locally 5 2 3 Radial attenuation of 4QPMs The intensity of off centred sources is also partially reduced The radial attenuation was measured to evaluate the impact of the Lyot spot on the Inner Working Angle and hence on the attenuation of an off axis point source Measurements were made for both masks and are presented in Figure 5 6 these plots are important to correct the photometry of off axis objects when looking at close companions For instance a companion lying at 0 1 from the primary has its flux absorbed by 50 in the Ks band and 40 in the H band 50990 VEE 0 0t t P PO LES Angulor distonce in arcseccods Figure 5 6 Radial attenuation of an off axis point source moved outwards of the mask centre in H left and Ks right The data are shown as symbols and the lines are from simulations Error bars correspond to the uncertainty in the intensity normalization with respect to the simulations 5 2 4 Contrast
119. hanged The total number of offset positions is defined in the parameter Number of offset positions This number can be different from the number of elements in the aforementioned lists Lists do not need to have the same length If the number of exposures is larger than the number of elements in a list the list is restarted from the beginning as many times as needed until the correct number of frames have been acquired The lists can have any length however having lists of different lengths can become extremely confusing It is good practice to use lists of equal length or lists with only one value when one parameter remains constant This template allows slit scanning across an object by defining a list of offsets in the Y direction 96 NaCo User s Manual VLT MAN ESO 14200 2761 If the parameter Return to Origin T F is set to true T the telescope returns to the starting position If not the telescope is not moved The total integration time excluding overheads is defined in seconds by DIT x NDIT x Number of offset positions x NEXPO per offset position 1024 1024 Y Acquisition Position f SN Slit Angle 45 degrees a N CONICA FOV S27 28 1 1 X Figure 7 8 An illustration of how the NACO spec obs GenericOffset template works The AO loop is off when the sky S is observed large filled in circles and on when the object O is observed small filled in circles The dashed line connecting
120. he instrument and the telescope The instrument operator observes the programs under the supervision of the visiting astronomer Visitors should be aware that up to 1 hour of their time can be taken by the observatory to comply with its calibration plan Typically only 15 minutes are needed The calibrations usually consist of twilight flat fields and imaging standards For spectroscopic observations the observatory automatically takes telluric standards for each setting used Visitors should think carefully about which tellutic standards fundamental to remove telluric features should be observed The observatory staff will help them make the right choice Even though Paranal is an excellent site bad weather or poor and fast seeing can occut Visitors should come with backup programs particularly if the targets are in the North where on some occasions the wind can be strong enough to prevent the telescope from pointing in that direction Visitors should also prepare targets with bright V lt 10 reference sources so that telescope time can be effectively used when the turbulence is fast 6 2 Active Optics versus Adaptive Optics Active optics is the active control of the primary and secondary mirrors of the telescope Adaptive optics is the correction of wavefront errors induced by atmospheric turbulence Although the instrument can run in closed loop without the active optics system controlling the primary and secondary mirrors one gets be
121. he offsets have to be entered manually as lists In this latter case the convention is that offsets are relative E g the following list of offsets RA offset list arcsec 0 10 10 20 20 DEC offset list arcsec 00000 will result in a first image without offset a second image in which the telescope was moved 10 arcsec East a third image at the original position etc Sometimes offsets may be defined in detector coordinates In that case a positive offset in X will move the image to the right X the telescope offset is therefore in the opposite direction All offsets ate defined in arcsec even the offsets that are defined in detector coordinates Therefore an offset of 10 in X will move the object 10 to the right 7 2 NaCo General templates 7 2 1 NACO all obs Rotate The NACO all obs Rotate template rotates the field of view and it has only one parameter the rotator offset angle The angle is in degrees and a positive angle will rotate the adaptor from North to Fast Hence objects in an image will rotate from North to West The angle is relative hence the position angle of the field at the end of the rotation will be the position angle of the field before the template was run plus the angle in the template The template can only be followed by imaging templates 79 NaCo User s Manual VLT MAN ESO 14200 2761 7 3 NaCo Acquisition templates Telescope presets can only be done via acquisition templates and all obse
122. how accurately the instrument induced polarisation can be removed from data 5 5 1 Calibration plan for polarimetry For polarimetric observations a variety of calibration frames will be taken archived and updated at regular intervals The calibrations are described in detail in the NaCo Calibration Plan o Twilight flats as described in section 5 1 3 Twilight flats are done without the polarimetric mask and without the polarizer However in visitor mode twilight flats with the half wave plate can be requested o Lamp flats as described in section 5 1 3 For polarimetric observations two sets of flats are taken For observations with the Wollaston the first set is without the polarimetric mask 44 NaCo User s Manual VLT MAN ESO 14200 2761 and polarizer and the second set is with these elements There are no internal lamp flats taken with the half wave plate o Detector darks in all readout modes and DIT 5 5 2 Pipeline for polarimetry Polarimetry is not supported by the pipeline 5 6 Sparse Aperture interferometric Masks SAM As part of the original design of the CONICA camera provision was made for the possibility of utilizing aperture masking interferometry in order to obtain the very highest angular resolutions at the diffraction limit Following highly successful demonstrations of the technique elsewhere both in the AO corrected and non AO case a proposal was submitted to ESO to install custom fabricated apertu
123. ide Star Acquisition 0 75 Initial Setup 2 AO Acquisition 5 SDI acquisition 1 Sub Total acquisition 11 75 Observation at 0 and 33 degrees 2x5x 27 6x10 0 7 2x7 3 14 6 Rotator Offset 1 Total 27 3 Overheads 173 Observation Number of offset positions x Offset overhead NDIT x DIT readout overhead 75 NaCo User s Manual VLT MAN ESO 14200 2761 7 NAOS CONICA TEMPLATES The instrument detector and telescope are controlled by Observing Blocks OBs which are made up of templates Templates are divided into three categories acquisition observation and calibration Usually OBs consist of an acquisition template and one or more observation templates for nighttime observations and in some limited cases an additional nighttime calibration template Only one acquisition template is allowed in an OB and therefore only one preset on sky It is not possible e g to group in the same OB observation templates on the science object and calibration template on a standard star Table 7 1 provides a short summary of the templates offered for P82 These templates should cover most needs If this is not the case users must contact the User Support Department usd help eso org well before the start of observations 7 1 General remarks and reminders Only parameters specific to NaCo are described The description of other parameters can be found in the P2PP User Manual http www eso org observing p2pp o We strongly
124. ieved either by rotating the entire instrument or by taking data with the half wave plate rotated by 22 5 degrees compared to previous data The beam separations for the different cameras are given in Table 5 8 The wavelength dependence of the beam separation shows that from 1 to 2 5um the Wollaston prism can be used for broadband application without loss of spatial resolution Within the K band for example the resulting chromatic error is about 86 mas The Wollaston can also be used with the LW filters however the beam separation is less and there is slight overlap between the ordinary and extraordinary beams Table 5 8 Beam separation of the Wollaston prism The average beam separation corresponds to about 3 3 on the sky Camera Separation pixels S13 254 S27 124 S54 62 Since the J band filter is in the same wheel as the Wollaston prism J band Polarimetric observations are not possible The instrument induced polarisation as for all Nasmyth instruments is a function of the parallactic angle it is generally of the order of 2 but can be as high as 4 If users do not take care in determining the instrument induced polarisation then it is not possible to get meaningful estimates of the polarisation unless sources are more than 3 polarised In general we recommend that users come as visitors if they wish to measure the polarisation of sources that are less than 5 At this stage we do not know
125. imes where detector readout noise dominates Earlier experiments with seeing limited telescopes before the advent of AO in the near IR had a magnitude limit of about 5 mag in K band cfr Bedding et al 1993 The Messenger 74 2 With CONICA s AO system we estimate that the useful magnitude limit for some types of observations could be as faint as 10 12 mag depending on the level of correction obtained Here we limit our discussion to two basic types of observation 1 imaging and 2 faint companion detection For both of these modes masking interferometry has demonstrated levels of performance which match or exceed those obtainable by any other means Further discussion of these strengths can be found in the sections below detailing the on sky performance obtained with SAM at CONICA 46 NaCo User s Manual VLT MAN ESO 14200 2761 5 6 2 Pupil tracking with SAM One additional aspect of experimental implementation that was requested in advance was the ability to drive the optical rotator and telescope control system in such a fashion that the image of the pupil within the CONICA camera is maintained fixed at a given orientation while the telescope tracks and slews to different stars This pupil tracking mode is crucial for experiments such as aperture masking where the occultation of one of the mask holes by the telescope spiders will cause highly detrimental loss of Fourier coverage and compromise the calibration propertie
126. ing The minimum DIT is 1 7927 seconds The detector mode refers to the setting of the array bias voltage and four modes have been defined HighSensitivity HighDynamic HighWellDepth and HighBackground The well depth and the number of hot pixels are directly related to the detector mode HighSensitivity has the fewest hot pixels but it has the smallest well depth Conversely HighBackground has the largest well depth but has many more hot pixels The former is used for long integrations in low background situations where cosmetic quality and low readout noise are paramount while the latter is used in high background situations where cosmetic quality is less important The detector mode is not a parameter that users can select It is set automatically and depends on the instrument setup For example all observations in FowlerNsamp will use HighSensitivity Details of how the detector modes are assigned are given in Table 5 11 The maximum allowed DIT is now unconstrained by the array However in practice the maximum DIT is defined by the need to get sky frames and this will be around 900 seconds Users should be aware that some of the observatory provided calibrations are only done in one readout mode For example standard star observations in the SW broad band filters will only be done in Double RdRstRd If users want to observe a standard in a mode that is not supported in the calibration plan they should submit their own OBs 58 N
127. ions along the slit and the spectra will fall at the same positions on on the detector Therefore even if you define some non zero value for the Jitter Box Width parameter it is recommended to give the Nod throw parameter different values between OBs so as to get the spectra at different positions across the array When defining the nod throw users are requested to ensure that other objects in the slit do not cause the spectra to overlap when the throw is executed The total number of frames is Number of AB or BA cycles x NEXPO per offset position x 2 95 NaCo User s Manual VLT MAN ESO 14200 2761 The total integration time excluding overheads is defined in seconds by DIT x NDIT x NEXPO per offset position x 2x Number of AB or BA cycles Table 7 17 Parameters of NACO_spec_obs_AutoNodOnS lit P2PP Label Default Values Description DIT NODEFAULT Detector Integration Time sec NDIT NODEFAULT Number of DITs Readout mode FowlerN samp Readout mode Jitter Box Width NODEFAULT Jitter Box Width Number of AB or BA cycles NODEFAULT One cycle is one object sky pair NEXPO per offset position 1 Number of exposures per offset position Nod Throw NODEFAULT Nod Throw in arcsec Return to Origin T F T Return to Origin Slit NODEFAULT Name of slit Spectroscopic Mode NODEFAULT Spectroscopic Mode 7 6 2 NACO spec obs GenericOffset This template is used for spectroscopy and has the flexibility of programming any sequence of tel
128. is important not to over specify the constraints as this reduces the chances of the Observing Block being executed For wavefront sensing in the IR and for reference sources that are brighter than V 16 the values for Lunar Illumination and Moon Angular Distance in the Constraint Sets of your OBs should be 1 0 and 30 respectively 6 4 Telescope control Most interactions with the telescope consist of telescope presets for acquisition telescope offsets during observations and M2 chopping for some LW observations Small offsets Le less than one arc minute are usually completed in 10 seconds of time ot less It is important to distinguish between the star that is used by the telescope for active optics and the reference object used by NAOS for wavefront sensing The active optics stars are automatically selected by the Telescope Control System and users do not have to worry about finding them The reference object used by NAOS for wavefront sensing and specified within the PS is chosen by the astronomer See Appendix B It is quite common to offset the telescope very frequently when observing with NAOS CONICA and since there are two stars that are used to control the system one for active optics and the other for adaptive optics as well as the scientific target users have to pay very special attention to the restrictions imposed by the system There are essentially two kinds of offsets The first is an offset that results in the NAO
129. iscard all the data currently stored in the interface However it does not alter any of the configuration files that have been saved to disk Only the files with an extension jnps can be loaded into the PS Once a previous session is loaded into the PS one should run the optimization again before exporting to P2PP otherwise a corrupted file may be exported and the observation may be impossible In case one forgot to save a session it is possible to copy the aocfg file into a jnps file and then import it as a session 9 5 10 Giving names to session P2PP and PSF files Each time a file is about to be saved one is asked to provide a name The default name is based on the target name but one may want to change it This does not affect the operations and may be convenient for the user However remember the files will be used by Unix based machines so one should avoid special characters spaces brackets etc in the names 9 5 11 Users preferences The Preferences menu gives access to configurable functionalities of the PS which are detailed below o Show tool tips every field in the GUI has an attached tool tip Though very useful when starting to use the PS this may be annoying for more experienced users This option allows one to switch them on off 120 NaCo User s Manual VLT MAN ESO 14200 2761 o Set working directory you can specify here the name of the directory where the output files are created by the PS the one
130. ld familiarize themselves with the contents of this table In particular the most critical choice will be between the N90C10 and N20C80 dichroics The former will result in higher Strehl ratios but much lower sensitivity particularly in the K band The N90C10 dichroic can also be selected with the visible WES in order to reduce the flux transmitted to CONICA for instance with a very bright source In a similar way the wavefront sensor can be selected This is where one can indicate the wish to use the laser guide star LGS Only if the WFS has been selected as LGS will an LGS mode be proposed to the user 112 NaCo User s Manual VLT MAN ESO 14200 2761 There are borderline cases when one has to decide whether to select LGS or NGS mode The limiting magnitude is currently 13 5 14 i e with AO reference stars which are fainter than this limit one should select LGS mode and keep the star as a tip tilt reference Brighter stars offer better performance in NGS mode When using the PS a good rule of thumb is the following if the expected Strehl ratio calculated for the NGS mode is 10 or higher stay with NGS Otherwise move to LGS Until further notice no mixed configurations or dual OBs are allowed if the first choice is LGS the second cannot be NGS with VIS WES Moreover only PIs that explicitly requested LGS in Phase I will be granted its use Target information consists of a name coordinates and proper motion For the prope
131. le 6 5 Users especially those in service mode should check them and make sure to take them into account for their Phase 1 amp 2 proposal Note that any LGS acquisition will last 10 minutes longer than the corresponding NGS acquisition i e 22 minutes for a polarimetric acquisition using the LGSF Some examples ate given below to illustrate how to compute overheads with NaCo In all examples we have assumed that the reference source used for AO and the target are the same Not all parameters of the listed templates are shown Only those that have an impact on the overheads ate listed 68 NaCo User s Manual VLT MAN ESO 14200 2761 6 18 Observing with the LGS At the time of updating this manual the LGS mode of NAOS is still poorly characterised Its use is for the time being recommended only for science programs that can take advantage of moderate Strehl ratios seeing enhancements to achieve their scientific goals From the past commissioning experience one advises to avoid LGS observations for objects with airmass above 1 5 for which the AO correction degrades strongly A natural guide star NGS is still required to correct for the tip tilt motions which are not sensed by the LGS The NGS has to be in the V magnitude range 12 17 and can be as far away as 40 from the science target however with decreasing performance with increasing distance At 40 distance about half the Strehl ratio is achieved as compared to
132. mas Figure 5 16 Likelihood for the presence of a secondary star as a function of its position At maximum likelihood the flux ratio between the main star and its companion is 1 29 0 14 in K band top and 1 47 0 24 in H band bottom 51 NaCo User s Manual VLT MAN ESO 14200 2761 AB Dor was observed between 1h17 and 1h42UT HD41371 was used for PSF calibration and was observed between 1h54 and 2h12UT For each one of these targets the data consist of two data cubes in each band 2 24 um and 1 75 um The cubes are sets of 100 exposures of 2 seconds integration time using a 512x512 windowing of the detector Seeing was around 1 5 but AO correction was nevertheless stable with occasional disruptions The 9 holes mask was used Correction for dark flat field and bad pixels was applied to our data An important step was to eliminate exposures were AO correction was unstable The frequency components visibilities and closure phases are then derived A binary system is fitted to the data and the likelihood computed Figure 5 16 gives the likelihood for the presence of a binary companion as a function of its relative position to the star A good fit was obtained for several different positions due to the regular Fourier sampling of the u v plane Because the minimum spacing between two holes is 1 73 meters images are obtained with a modulo 1 73 A rad This corresponds to 208 mas in H and 267 mas in K By using data from the two
133. n of the deformation of the wavefront WF by adaptive optics AO Figure 3 1 The wavefront sensor WFS measures WF distortions and these measurements are processed by a real time computer RTC The RTC controls a deformable mirror DM and corrects the WF distortions The DM is a continuous thin plate mirror mounted on a set of piezoelectric actuators that push and pull on the back of the mirror Because of the significant reduction in the WF error by AO correction it is possible to record images with exposure times that are significantly longer than the turbulence correlation time The WF error directly determines the quality of the formed image One of the main parameters characterizing this image quality is the Strehl ratio SR which basically corresponds to the amount of light contained in the diffraction limited core relative to the total flux An AO system is a servo loop system working in closed loop The DM flattens the incoming WF and the WFS measures the residual WF error The WFS in NAOS uses a Shack Hartmann screen It consists of a lenslet array that samples the incoming WF in a pupil plane Each lenslet forms an image of the object and the displacement of the image gives an estimate of the WF slope at that lenslet A good feature of this WFS is that it works with white light extended sources and very faint stars The performance of an AO system is directly related to the number of lenslets in the lenslet array the number of act
134. n prism A drawing of the polarimetric mask is displayed on the RTD and is superimposed on the image of the field The centring of the target is then done interactively Acquisition must be done with the L27 objective for LW filters or the S27 objective for SW filters The subsequent polatimetric science templates allow one to set the angle before each template starts This template records an image of the field after the acquisition has been completed If three images are recorded then the first two are images of the reference and they are used by the operator to classify the OB Table 7 7 describes the parameters of this template Table 7 7 Parameters of NACO_img_acq_Polarimetry P2PP Label Default Values Description DIT NODEFAULT Detector Integration Time sec NDIT NODEFAULT Number of DITs Type of AO Observation LGS NGS NODEFAULT LGS or NGS observation type PSF Reference T F F Set to T if it is a PSF reference star Pupil Tracking Mode T F F Always set to F PT not suppotted RA offset arcsec 5 RA offset for sky image DEC offset arcsec 5 DEC offset for sky image Position angle on sky 0 Position angle Add Velocity Alpha 0 Additional tracking velocity in arcsec sec Add Velocity Delta 0 Additional tracking velocity in arcsec sec Filter NODEFAULT Filter name Neutral Density Filter Full Neutral density Filter Full none Camera 27 Camera name NAOS parameter file NODEFAULT NAOS aocfg file from the JNPS 85 NaCo U
135. nds are spent at each end of the nod To compute the actual integration time from the information provided in the FITS header youneed to compute DIT x NDIT x 2 x Number of cycles x Number of AB or BA cycles x 2 Table 7 13 parameters of NACO_img_obs_AutoChopNod P2PP Label Default Values Description Chop Nodding coordinate NODEFAULT SKY or DETECTOR coordinates Chop Position Angle NODEFAULT Chop Position angle deg Chop Throw NODEFAULT M2 Chop Throw arcsec Integration time minutes NODEFAULT Total Integration Time Jitter Box Width NODEFAULT Jitter box width Return to Origin T F T Return to Origin at the end of the template Filter NODEFAULT Filter name Neuttal Density Filter Full Neutral density filter Full none Camera NODEFAULT Camera Name 7 44 NACO img obs FixedSkyOffset This template moves the telescope alternatively between object and sky positions The object positions are randomly distributed around the initial telescope position and within a box whose dimensions are set by the parameter Jitter Box Width in arcsec The sky positions are randomly distributed around a position that is set at a constant distance defined by the parameters Sky offset in DEC and Sky offset in RA from the original telescope position and within a box whose dimensions are set by the parameter Jitter Box Width in arcsec The object positions will be observed with the AO loop
136. nps After initialization the main GUI will appear The start up procedure partly depends on the contents of your preferences file which is created in your home directory when you start the PS for the first time This file called jnpscf contains the user s choices for several items some of which can be accessed via the Preferences menu of the main GUI 9 2 Graphical User Interface Overview The GUI that appears after the initialization phase is depicted in Figure 9 1 The panel is divided into three areas which are from top to bottom o The menu bar giving access to file telated operations and other miscellaneous functionalities see following sections 111 NaCo User s Manual VLT MAN ESO 14200 2761 o The main panel divided in four sub areas which respectively deal with the science target the reference object the sky conditions and resulting performance image quality o The action area gathering general actions such as requests for optimization or creation of the P2PP parameter file and the HTML file for the ETC a Objects Preferences rlarget amp Instrument Setup CONICA Filter Ks Observing Wavelength 2 13 Dichroic FREE z Wavefront Sensar FREE Target Name TesiSource Epoch 2000 0 Equinox 20000 Raf oT p2 0 Prop Mot RA 0045 aresecyear DEC 33 22 Prop Mot DEC 0 67 arcsecyvar sy Co lt amp Up Down Delete Clearall Duplicate Seeing at zenith 0 3 Se
137. nstrument software Table 5 1 List of available Cameras with plate scales fields of view and wavelength ranges Camera Scale FOV Spectral Range mas pixel arcsec microns S13 13 72 14x14 1 0 2 5 S27 27 15 28x28 1 0 2 5 S54 54 6 56x56 1 0 2 5 SDI 17 32 8x8 1 6 L27 27 19 28x28 2 5 5 0 L54 54 9 56x56 2 5 5 0 5 1 2 Filters All but one of the CONICA filters Table 5 1 and Table 5 2 are mounted on two filter wheels Transmission curves of several filters are given in Appendix A The J band filter is mounted on a third wheel that also contains the Wollaston prism and the wire grids so J band polarimetric observations are not possible with NaCo In this manual filters with central wavelengths longer than 2 5 microns will be referred to as LW filters and filters with wavelengths shorter than 2 5 microns will be referred to as SW filters Not all filter and camera combinations are supported For the 13 S27 and S54 cameras all SW filters can be used For the L27 camera the NB 3 74 NB 4 05 Lp and Mp filters can be used For the L54 camera only the NB 3 74 and NB 4 05 filters can be used Observations with the Mp filter are restricted to a FOV of 14 x 14 corresponding to a detector window of 512 x 512 The FOV is smaller in Mp than in other LW filters because the background in Mp is considerably higher the integration time has to be reduced which can only be done by windowing the array
138. object and sky are sampled as desired for one angle only The template can be restarted with another orientation on the sky for another series of exposures At least two different orientations separated by 45 degrees are required for computing the Stokes parameters To image the entire field of view at one position angle one must take great care with the offsets The opaque and transmitting parts of the mask have slightly different widths The opaque strips have a width of 3 9 and the transmitting strips have a width of 3 1 An example of how one may choose to image the entire field of view is given in Figure 7 9 The total integration time excluding overheads is defined in seconds by DIT x NDIT x NEXPO per offset pos x Number of offset pos x number of rotator pos Table 7 20 Parameters of NACO_pol_obs_GenericOffset P2PP Label Default Values Description DIT NODEFAULT Detector Integration Time sec NDIT NODEFAULT Number of DITs Readout mode Double_RdRstRd Readout mode NEXPO per offset position 1 Number of exposures per offset position Number of offset positions NODEFAULT Number of offset positions Observation type O or S NODEFAULT O is in closed loop S in open loop Offset coordinates NODEFAULT SKY or DETECTOR List of offset in X NODEFAULT Offsets in arcsec List of offset in Y NODEFAULT Offsets in arcsec Return to the original rotator F Return to original rotator position at the position T F end of the template List of po
139. ode T F F Set to T for Pupil tracking observations RA offset arcsec 5 RA offset for sky image DEC offset arcsec 5 DEC offset for sky image Position angle on sky 0 Position angle or pupil angle in degrees Add Velocity Alpha 0 Additional tracking velocity in arcsec sec Add Velocity Delta 0 Additional tracking velocity in arcsec sec Filter NODEFAULT Filter name e g Ks Mask NODEFAULT Coronagraphic mask Neutral Density Filter Full Neutral density Filter Full none Camera NODEFAULT Camera Name e g S27 NAOS Parameter file NODEFAULT NAOS aocfg file from JNPS 7 3 6 NACO img acq SDIMoveToMask This template does a telescope preset which is followed by interactive acquisition of the object behind the 4QPM_H in combination with the SDI camera It must be followed by the dedicated SDI 4 template which uses the same instrument setup with the possible exception for the use of the neutral density filter ND_Short for the acquisition of very bright targets The use of the H band filter is recommended The template records the following frames o One flat on halogen lamp is on and one flat off image these images can be used for flat fielding the subsequent science frames o An image of the star off the mask 2 off with the ND filter inserted if specified in the initial setup and an image of the sky these images can be used as PSF calibrator Then the following steps are performed o Rough offset to position the star
140. olved applications since there is currently no way to time stamp each single DIT There are stringent limitations to the use of this mode in particular it will only be offered in combination with basic imaging no LGS SDI coronagraphy and SAM This mode is only offered for VM runs Additional advantage of the cube mode is the much smaller overheads needed to save large quantities of frames When in the past a user would select a certain number of exposures per offset by means of the NEXP parameter now one can select cube mode and save all the images in one frame saving the time needed to save each file 16 17 sec The size of each cube is limited by the maximum file size accepted by our flavour of Linux 512 MB Therefore given a certain detector window this fixes the maximum number of planes that can be saved in a cube i e NDIT Cube mode is offered in combination with 5 different window sizes Note that since windowing is done on chip NY NX 2 Table 5 12 lists the available windows the minimum DIT and the maximum NDIT for Double_RdRstRd and HighDynamic DCR HD We intend to offer cube mode also with FowlerNsamp and Uncorrelated read At the time of writing these modes were still being characterized Interested users are encouraged to check on the web pages or to contact the Instrument Team at naco eso org 59 NaCo User s Manual VLT MAN ESO 14200 2761 Table 5 12 characteristics of cube mode
141. on 12 75 Observations at 0 and 22 5 degrees 2x 5x 27 6x 10 2 2x8 3 16 4 HWP rotation 0 25 Total min 29 6 Overheads 196 Observation Number of offset positionsx Offset overhead NDITx DIT readout overhead 73 NaCo User s Manual VLT MAN ESO 14200 2761 Table 6 12 Example 6 SW coronagraphy of a bright source with Double_RdRstRd Template parameters Acquisition Template NACO_img_acq_MoveToMask Observation Template NACO coro obs Stare DIT 10 sec NDIT for the OBJECT positions 6 NDIT for the SKY positions 5 Number of AB cycles 2 Number of exposures OBJECT Only 10 Number of offset positions SKY only 4 Readout Mode Double R dRstRd Execution Time min Preset 3 Guide Star Acquisition 0 75 Initial Setup 2 AO Acquisition 5 Coronagrahic acquisition 2 Sub Total acquisition 12 75 Observations 36 2x 10x 6x10 0 7 9x16 27 4x 5x10 0 7 27 Total min 49 Overheads 84 Observation Number of AB cycles x Number of exposures OBJECT x DITxNDIT readout overhead Number of exposures OBJECT 1 x time between frames without offset Offset overhead Number of offset positions SSKY x DITXNDIT readout overhead offset overhead Table 6 13 Example 7 LW coronagraphy of a bright source Template parameters Acquisition Template NACO_img_acq_MoveToMask Observation Template NACO_coro_obs_AutoChopNod
142. onger to reach background limiting performance Additionally the fields of view are smaller so large scale changes in the sky background are less noticeable in CONICA than in ISAAC Thus the typical integration time and the typical amount of time between telescope offsets will be larger for CONICA 16 NaCo User s Manual VLT MAN ESO 14200 2761 3 4 Transmission and background The transmission of the Earth s atmosphere in the 1 5 um region is shown in Figure 3 2 the X J H K L and M bands correspond to atmospheric windows which are approximately centred at 1 1 25 1 65 2 2 3 6 and 4 8 um The absorption is mostly due to water and carbon dioxide and it varies with zenith distance and the amount of water vapour As regards observations with NaCo the sky background can be split into two regions Below 2 2 um the sky background is dominated by OH emission that originates at an altitude of 80 km At longer wavelengths the thermal background of the atmosphere and telescope dominate 3 5 Background subtraction Subtraction of the background is critical to the success of observing in the IR and special observing techniques have been developed to do it The techniques depend on the type of observation and on the wavelength region at which one is observing For imaging observations short ward of 4 2 microns and for regions that are relatively un crowded Le tens of point sources in 20 square arcsec or moderately extended objects the
143. op throw Fabry Perot will not be offered SDI is decommissioned and replaced by SDI Polarimetry is offered with the Wollaston_00 and retarder plate only Special calibrations all observations requesting special calibrations will be moved to VM Exceptions to this rule will be considered on a case by case basis during technical feasibility 14 NaCo User s Manual VLT MAN ESO 14200 2761 3 OBSERVING WITH ADAPTIVE OPTICS IN THE INFRARED 3 1 Atmospheric turbulence The VLT Very Large Telescope has a diffraction limited resolution of A D 0 057 at A 2 2 um But the resolution is severely limited by atmospheric turbulence to 4 t 0 7 where r is the Fried parameter The Fried parameter is directly linked to the strength of the turbulence and it depends on the wavelength as 4 For average observing conditions r is typically 60 cm at 2 2 um The correlation time of the turbulence To is related to f and the speed at which the turbulent air travels For a wind speed of 10 m s the correlation time is of the order of 60 ms at 2 2 um Both tyand fp are critical parameters The larger they are the more stable the atmosphere is and the better the performance of NAOS will be Atmospheric conditions are better suited to AO observations during the summer months in Paranal with larger Ty and to 3 2 Adaptive optics A powerful technique in overcoming the degrading effects of atmospheric turbulence is real time compensatio
144. or lucky imaging type of observations where one wants to select the best frames out of a set before co adding them The mode is not suited for time resolved applications since we have no way to time stamp each single DIT frame There are stringent limitations to the use of this mode in particular it will only be offered in combination with basic imaging no LGS This mode is only offered for VM proposals e Pupil tracking mode for imaging applications includes coronagraphy and SDI Tentatively offered pending commissioning Pupil tracking mode is being implemented to support SAM but given the demand from the community it will be tentatively offered for use 13 NaCo User s Manual VLT MAN ESO 14200 2761 with imaging and coronagraphic observations In this mode the telescope independently from NaCo tracks the pupil instead of the field This new tracking mode opens the possibility to do Angular Differential Imaging ADD a high contrast imaging technique that reduces quasi static speckle noise and facilitates the detection of nearby companions More work is needed to characterize the mode and to make it available to the community but it is hoped that full or partial availability will be ready in time for P82 Given its complexity and novelty pupil tracking is only offered in VM Chopping will be offered again in P82 for both Mp and Lp There are more stringent limitations on the brightness of the AO star and on the size of the ch
145. or sky in arcsec Sky offset in DEC NODEFAULT DEC offsets for sky in arcsec Filter NODEFAULT Filter Name Mask Position NODEFAULT Coronagtaphic mask Camera NODEFAULT Camera Name 7 8 2 NACO coro obs Astro This template is used for coronagraphic observations 103 NaCo User s Manual VLT MAN ESO 14200 2761 It runs after a normal coronagraphic acquisition It takes NEXPO Obj only images of a target behind the coronagraphic mask without moving the telescope Then the coronagraphic mask istemoved and NOFF img 1 are taken The last offset provided in the NOFF IMG list moves the telescope onto the sky position Generic offset principle There the mask is inserted again and on an auto jitter manner NOFF SKY images are taken on sky The idea is to get images of the target with and without the coronagtaphic mask Since most sources are too bright for simple imaging there exists the possibility to define a different filter set up for the imaging part of the template The number of coronagtaphic images to be taken on the source is defined by NEXPO CORO NOFF CORO defines the number of sky images to be taken with the coronagraphic mask The integration time DIT CORO is forced to be identical for all data taken with the coronagtaphic mask but NDIT can be different for images with the target NDIT Obj and on sky NDIT Sky The Readout mode can be selected but remains the same throughout all the template For the im
146. otal integration time excluding overheads is defined in seconds by DIT x NDIT for the OBJECT positions x Number of Exposures Object Only NDIT for the SKY positions x Number of offset positions Sky only x Number of AB cycles If Number of offset positions Sky only is set to zero the sky is not observed In this case the total integration time is DIT x NDIT for the OBJECT positions Number of Exposures Object Only and all other parameters are ignored In this way the template takes a series of exposures of the target without offsets However sky subtraction is almost always required so this option will probably only be used in very special circumstances Note that an additional overhead of 2 minutes for target re centring has to be considered everytime that Number of Exposures Object Only is greater than 1 Table 7 26 Parameters of NACO_sdi4_obs_Stare P2PP Label Default Values Description DIT NODEFAULT Detector Integration Time sec Readout mode Double_RdRstRd Readout mode Window Size 1024 Size of the window Store Data Cube T F F Data cube flag Jitter Box Width NODEFAULT Jitter box width sky only Number of AB cycles NODEFAULT Number of AB cycles e g 2 for ABAB NDIT for OBJECT positions NODEFAULT Num of DITss per object position NDIT for SKY positions NODEFAULT Num of DITs per sky position Number of exposures object NODEFAULT Number of exposures on target only Number of offset positions sky NODEFAULT
147. otator mode 80 NaCo User s Manual VLT MAN ESO 14200 2761 7 3 2 NACO img acq MoveToPixel This template does a telescope preset and is followed by interactive centring of the object It should be used for normal imaging It must be followed by an imaging template Because the objectives are not aligned with respect to each other we recommend that the acquisition template and subsequent observing templates use the same objective In service mode it is mandatory that users provide detailed information for the field centring on their Finding Charts and or in their README file Table 7 2 describes the parameters of this template In order for faint objects to be clearly seen an image of the sky is acquired in an offset position defined by the RA offset arcsec and DEC offset arcsec parameters This image is then subtracted from all images that are subsequently displayed on the RTD The integration time for these acquisition images is defined by the DIT and NDIT parameters This template records an image of the field after the acquisition has been completed On some occasions two additional Br y images of the AO reference source which are used by the operator to help in classifying the OB are also taken Table 7 2 Parameters of NACO_img_acq_MoveToPixel P2PP Label Default Values Description DIT NODEFAULT Detector Integration Time sec NDIT NODEFAULT Number of DITs Type of AO Observation LGS NGS NODEFAULT LGS or N
148. otometric standards with the masks that are held by the wires C 0 7 and C 1 4 In this case the masks will not be inserted in the focal plane but the correct pupil mask will Table 7 25 describes the parameters of this template Table 7 25 Parameters of NACO_coro_cal_StandardS tar P2PP Label Default Values Description DIT NODEFAULT Detector Integration Time sec NDIT NODEFAULT Number of DITs Readout mode Double_RdRstRd Readout mode Window Size 1024 Size of the window Store Data Cube T F F Data cube flag NEXPO per offset position 1 Number of exposures per offset position Number of offset positions NODEFAULT Number of offset positions List of offsets in X NODEFAULT Offsets in arcsec List of offsets in Y NODEFAULT Offsets in arcsec Filter NODEFAULT Filter name Mask psition C_0 7_sep_10 Coronagraphic mask Camera NODEFAULT Camera Name 7 9 NaCo SDI 4 scientific templates For SDI 4 observations the readout mode of the detector should be set to either Double RdRstRd or to FowlerNsamp 7 91 NACO sdi4 obs Stare This template is used for SDI 4 observations and it moves the telescope alternatively between a fixed object position and a sky position The parameter Number of AB or BA cycles defines the number of times this is done but unlike the NACO spec obs AutoNodOnSlit and NCO img obs FixedSkyOffset templates the sequence is ABABAB and not ABBAAB for the example in which the Number of AB or BA cycles is set to 3 This part o
149. ount of vignetting depend on the mask and the objective Coronagraphic images with 4QPM and broadband filters provide a marginal improvement of contrast at a given radius although a significant maximum attenuation 20 200 depending on coronagraphs enable large signal to noise ratio with no need of saturation large fraction of the flux is therefore left in the focal plane composed with a dynamical halo averaging over time 34 NaCo User s Manual VLT MAN ESO 14200 2761 and fluctuating too plus a quasi static halo corresponding to optical aberrations along the optical train from telescope to detector Figure 5 9 Radial profile for the PSF the 4QPM and the 0 7 Lyot obtained with a natural star in 2004 It is recommended here to observe a reference star to calibrate these 2 halos The reference star is chosen with same visible and IR magnitudes to ensure similar AO correction and similar SNR in the image More important the reference MUST be observed with the same parallactic angle to have the same static speckle pattern which result from interaction between telescope and instrument aberrations and to match the spider spikes position in the images In practice the reference star has the same declination as the target but a right ascension which is that of the star plus or minus the OB duration reference is observed for the same amount of time as the target In general it is possible to find a reference star within less than
150. position angle of the slit should be set so that both the reference source and science target are in the slit at the same time These offsets should not be confused with the RA offset arcsec and DEC offset arcsec offsets which are used to define the offset between the target and a sky image which is subsequently subtracted from all images 82 NaCo User s Manual VLT MAN ESO 14200 2761 This template records between 2 and 5 images to disk On some occasions the operator will record two images of the AO reference which are used to classify the OB If this is the case the image of the slit will be the third frame recorded to disk otherwise it will be first The next image either the 2nd or the 4th image recorded to disk is an image of the acquisition target after it has been centred If reference offsets are used an additional image either the 3rd or the 5th image recorded to disk is taken after the reference offset Table 7 4 parameters of NACO img acqg MoveToS lit P2PP Label Default Values Description DIT NODEFAULT Detector Integration Time sec NDIT NODEFAULT Number of DITs Type of AO Observation LGS NGS NODEFAULT LGS or NGS observation type PSF Reference T F F Set to T if it is a PSF reference star Pupil Tracking Mode T F F Always set to F PT not supported Alpha offset from Ref star 0 Offset from reference star arcsec Delta offset from Ref star 0 Offset from reference star arcsec RA offset arcsec 5 RA
151. r X 040 400 40 Camera S27 List of offsets in DEC or Y 0080 8 808 89 NaCo User s Manual VLT MAN ESO 14200 2761 7 4 3 NACO img obs AutoChopNod This template combines imaging with M2 chopping and telescope nodding It can only be used with the LW filters The number of nodding cycles is referred to as Number of AB or BA cycles and one cycle commonly called an AB cycle consists of two exposures one at each end of the nod The orientation of the chopping is defined with the Chop Position Angle parameter This parameter can be defined in terms of SKY or DETECTOR coordinates with the Chop Nodding Coordinate parameter Additionally it is possible to jitter between ABBA cycles but not between AB or BA cycles The amount of jitter between ABBA cycles is defined by the Jitter Box Width parameter in arcsec For the removal of hot pixels it is essential that Jitter Box Width be set to a non zero value If the parameter Return to Origin T F is set to true T the telescope moves back to its original position at the end of the template If not the telescope is not moved The total integration time excluding overheads is defined in minutes In general the user will get slightly more or slightly less time than what was specified in the OB This is because the DIT is set so that the detector does not saturate the number of NDITs is set by the chopping frequency and the number of cycles is set so that approximately 30 to 60 seco
152. r extended objects with either a visible or an IR wavefront sensors It can also use a Laser Guide Star LGS Beacon and a natural Tip Tilt source ITS to provide AO correction with somewhat degraded performance with respect to NGS CONICA Section 5 is an Infra Red IR 1 5 um imager and spectrograph fed by NAOS It is capable of imaging long slit spectroscopy simultaneous differential imaging SDI coronagraphy polarimetry and sparse aperture interferometry with several different plate scales filters and options e g cube mode for lucky imaging pupil tracking for imaging coronagraphy and SDI The offered modes for P82 are listed in Table 2 1 NaCo can be used in Service SM or Visitor Mode VM The Observatory provides daily calibrations as the NaCo Calibration Plan Pipelines for quick look data reduction are available for some modes of the instrument Table 2 1 Main modes and parameters of NaCo Adaptive Optics Performance 40 Strehl ratio in K under good atmospheric conditions and with a reference object of V 10 mag or K 6 mag Imaging Broad and narrow band filters in the 1 5 um region with 14 56 fields of view and 13 54 mas pixel scales Simultaneous Differential Imaging SDI VM only Coronagraphy Occulting masks of various diameters 4 quadrant phase masks 4QPM_H 4QPM_K VM only Simultaneous Differential Imaging plus Coronagraphy SDI amp 4QPM_H VM only Spectroscopy Long slit and
153. r motion to be taken into account it is compulsory to provide both epoch and equinox for which the coordinates are provided The corresponding coordinates at the time of observation does correspond to the precessed coordinates at the mean epoch for a given period i e 2007 0 for P78 2007 5 for P79 and so on this is the hard coded epoch of the reference target The epoch of the science target is a free parameter to set between 1850 amp 2100 The target and AO reference star can have different proper motion It is however assumed that the coordinates are given for the same equinox 9 4 Sky Conditions The user characterizes the observing conditions via two parameters the seeing at Zenith and measured at 0 5m and the airmass The on axis quantities such as the seeing on the reference are automatically computed from these two parameters and some assumptions about the average wind speed and isoplanatic angle on Paranal The Fried parameter r and the isoplanatic angle 0 ate also displayed All on axis quantities are computed at 0 5 um 9 5 Reference Objects The information about reference objects is gathered on the right hand part of the main GUI For LGS operations the natural guide star for tip tilt correction TTS has to be specified Ease of operations requires that only one TTS can be specified per LGS OB 9 5 1 Handling several reference objects It is possible to keep a list of several possible reference objects
154. r of half wave plate angle x Number of offset pos The angle of the HWP used is reported in the FITS header under INS RETA2 NAME Previously this keyword did not exist The angle of the HWP can be retrieved from INS ADC1 ENC HWP encoder via the following formula HWP angle HWP encoder 205 4096 360 modulo 4096 Example angles of 0 amp 22 5 correspond to INS ADC1 ENC 3891 amp 51 respectively This information remains available from the FITS header Table 7 21 Parameters of NACO_pol_obs_Retarder P2PP Label Default Values Description DIT NODEFAULT Detector Integration Time sec NDIT NODEFAULT Number of DITs Readout mode Double_RdRstRd Readout mode NEXPO per offset position 1 Number of exposures per offset position Number of offset positions NODEFAULT Number of offset positions Observation type O or S NODEFAULT O is in closed loop S in open loop List of offset in X NODEFAULT Offsets in arcsec List of offset in Y NODEFAULT Offsets in arcsec List of position angle offsets NODEFAULT List of HWP angles Filter NODEFAULT Filter Name Mask NODEFAULT Set to Wollaston_00 Neutral density filter Full Neutral Density filter Camera NODEFAULT Camera Name Note that Mask should always be set to Wallaston_00 101 NaCo User s Manual VLT MAN ESO 14200 2761 7 7 3 NACO pol cal StandardStar This template should be used to observe polarimettic standards that do not require chopping It is strictly equivalent to
155. ra have been taken In general the difference between night and day time calibrations is small and most users will not need to take these calibrations 5 4 6 Pipeline for spectroscopy Pending successful commissioning in P82 we will offer a spectroscopic pipeline The final product will be a flat fielded wavelength calibrated combined spectrum 43 NaCo User s Manual VLT MAN ESO 14200 2761 5 5 Polarimetry A Wollaston prism is available for imaging polarimetry as well as a turnable half wave plate The latter is installed in the entrance wheel of CONICA where the calibration mirror is situated Internal calibrations with the half wave plate are thus impossible The Wollaston splits the incoming light into ordinary and extraordinary beams An image taken with the Wollaston prism will contain two images of every object To avoid sources overlapping a special mask consisting of alternating opaque and transmitting strips is inserted at the focal plane In a single exposure at least half the field will be missing so that three exposures with telescope offsets in between are required to image one field Sample flat fields with the special polarimetric mask in the focal plane are available from the NaCo web pages To measure the Stokes parameters and hence the degree and position angle of polarisation a second set of images with the Wollaston prism rotated by 45 degrees with respect to the first pair are required This can be ach
156. re masks into the pupil wheel of CONICA The design of aperture masks for a telescope needs to take into account several complicating factors For a given observation there are trade offs between various parameters which means that a range of different masks can be used in order to tailor the experiment to somewhat varying targets and science The factors relevnt to mask design include The desired Fourier coverage especially the shortest amp longest baseline required The bandwidth of the optical passband to be used for observations The apparent brightness of the target star The readout noise properties of the detector The degree of correction provided by the AO system In order to span a promising range of observational parameter space five masks were fabricated and the physical properties of the masks is illustrated in Figure 5 13 below They were fabricated by precision laser machining onto 0 2 mm steel stock The outer diameter of the final masks was 20 mm to fit within the CONICA pupil wheel slots Figure 5 13 Mechanical drawings of the five aperture masks installed in the CONICA camera In general the more holes appear in the mask then the smaller the holes must be to preserve non redundancy and consequently the less light that is passed by the mask The mask to the left shows the 18holes configuration which yields excellent Fourier coverage but which does not pass a large fraction of the incident light In order to access s
157. reviously and therefore the spectral leakage at the centre is smaller with SDI There is a clear improvement of almost a factor of 10 to use a 4QPM with SDI at high Strehl regime In addition to the fact that the signal to noise ratio is improved since longer integration time are possible the use of a coronagraph is known to be theoretically more favourable to differential imaging as demonstrated here 37 NaCo User s Manual VLT MAN ESO 14200 2761 4QPM_H 4 3 By NAN 4QPM_H_SDI 3 AN 4QPMH SDI 0 2 Angular distance in arcsec Angular distance in orcsec Figure 5 11 Radial profiles for the PSF solid the 4QPM image dotted and the SDI processing for PSFs dash dotted and 4QPM images dashed Colors are for o Az ted Ao As green M r blue s purple Left plot is for SDI and right plot is for SDI 5 3 2 Tests with 4QPM SDI 4 and rotation In the following section the relative merits of different observing techniques with 4QPM and SDI 4 are discussed this analysis was performed by the commissioning team The tests were performed on sky on a star and a reference and the results presented in Figure 5 12 In this figure we compare the detection levels that can be reached with the classical no SDI coronagraphic imaging using reference subtraction or not with SDI 4 using subtraction of SDI images of the reference or not The effect of roll averaging is also studied The r
158. right targets or perhaps a few tens of longer exposure frames 1 10 sec More details on cube mode can be found in section 5 8 Given the very small useful science field of view it is generally not necessary to read the entire 1024 pixel array In fact normally only a 256 square pixel region would be sufficient In addition to saving on data storage the smaller sub arrays can be read out faster and with a lower noise readout strategy Arrays of size 1024 512 and 256 can be read out in 0 34 0 11 0 04 seconds respectively in Double_RdRstRd Although for some of the brightest targets there may be good arguments for pursuing a 256 squate sub array we have chosen as the commissioning standard a 512x514 sub array The main advantage of this is that the image of the science target can be dithered between two separate quadrants on successive data cube integrations Thus while collecting data in one quadrant we are collecting a sky background frame in another quadrant at the same time 5 6 4 SAM with LW filters Operation in the 3 5 micron region using the long wavelength filters offered within CONICA is straightforward This was commissioned using the L27 camera which adequately samples the fringes and has optical components optimized for this region For the shorter wavelength operation only the S13 was used again to ensure adequate sampling of the fringes We have found that special strategies such as chopping to remove sky fluct
159. roscopic template After the AO reference has been acquired the slit is placed into the beam and an image is recorded The slit position is computed the slit is removed and a drawing of the slit is superimposed on the image of the field The centring of the target is then done interactively The template also allows one to place two objects into the slit without the requirement of calculating the position angle beforehand In such cases the acquisition strategy should be adequately explained in the README file and those targets which should be placed in the slit should be clearly designated on the Finding Chart and their position on the slit clearly indicated To save time during the acquisition we recommend that users enter an estimate of the position angle into the acquisition template Table 7 4 describes the parameters of this template The Alpha offset from Ref Star and Delta offset from Ref Stat parameters allow the user to define a telescope offset when the acquisition is made on a bright reference object That is once the reference object has been acquired and centred in the slit the offsets defined here will offset the telescope so as to bring the desired target into the slit Given the accuracy at which the offsets are likely to be defined the smallest slit is only 86 mas wide so the computed offsets have to be better than a few tens of mas we do not recommend this option to users If there is no other option then the
160. rs are invited to study this table carefully The N90C10 can be used with the visible WFS and serves as a neutral density filter for CONICA A field selector FS is placed just after the WFS input focus in order to select the reference object for WF sensing The FS also allows object tracking pre calibrated flexure compensation and counter chopping It is made up of two parallel tip tilt mirrors working in closed loop to achieve a very high angular stability Two WF sensors are implemented in NAOS one operating in the visible and one in the near IR An off axis natural guide star NGS can be selected anywhere within a 110 arcsec diameter field of view FOV facilitating a target to reference distance of up to 55 arcsec NAOS allows WF sensing with faint NGS and extended objects but with lower performance Observations of very bright objects are possible with the visible WFS using neutral density filters Note that these neutral density filters are distinct from the neutral density filters of CONICA and are not selectable within the NAOS PS software or within P2PP They are linked to the first three available AO modes 1 1 1 2 and 1 3 The two WF sensors are of the Shack Hartmann type For the visible WFS two configurations are available a 14x14 lenslet array with 144 valid sub apertures and a 7X7 lenslet array with 36 valid sub apertures For the IR WFS three configurations are available a 14x14 lenslet array with 144 valid sub aperture
161. rving blocks must start with one There are seven acquisition templates one for imaging and one each for SDI imaging spectroscopy coronagraphy SDI 4 polarimetry and SAM They are listed in Table 7 1 All acquisition templates preset the telescope to the AO reference star set up NAOS and CONICA close the loop and acquire the science target All acquisition templates require a NAOS parameter file a k a aocfg file which contains information about the target the reference source the NAOS setup and other ancillary data Once this file is loaded the target fields in P2PP will contain the target coordinates The acquisition templates can take anywhere from one to five images during the acquisition process See the description of the individual acquisition templates for a description of what kind of images are recorded In general it is not necessary for the acquisition and the subsequent observation templates to have the same DIT and NDIT nor the same filter but it is recommended Exceptions are SAM where the mask cannot change from acquisition to science SDI 4 and the 4QPMs which once inserted are never removed from the optical path The detector and readout modes are not parameters of the acquisition templates They are automatically set and they depend on the filter For LW filters the readout mode is set to Uncorr and the detector mode is set to HighDynamic For all other filters the readout mode is set to Double_RdRstRd and
162. s and two 7X7 lenslet arrays with 36 valid sub apertures Independent of which Shack Hartmann sensor is being used all 185 actuators on the DM are used The FOV the temporal sampling frequency and the pixel scale of the WFS can also be optimized providing a good performance over a large magnitude range Characteristics of both WFS are given in Table 4 2 Table 4 2 Wavefront sensors characteristics Characteristics Visible WFS Infrared WFS Wavelength range 0 45 1 0 um 0 8 2 5 um FOV per lenslet 14x14 2 32 5 15 7x7 4 64 4 8 VO and 5 5 V1 Magnitude range 14x14 0 12 4 9 7x7 12 16 7 9 12 Detector 128x128 EEV CCD 1024x1024 Rockwell Hawaii 4 2 NAOS Performance The level of the AO correction depends on a large number of factors such as seeing the speed of the turbulence the airmass the brightness and morphology of the reference object the distance between the reference object and target and instrument performance 1 With the N20C80 dichroic The magnitude ranges with the N90C10 dichroic are approximately 1 5 magnitudes fainter 21 NaCo User s Manual VLT MAN ESO 14200 2761 The performance of NAOS is summarised in Table 4 3 The preparation software should be used for more detailed predictions and simulated PSFs Table 4 3 Summary of NaCo Strebl ratios at 2 2 microns for an AO reference star at an airmass of 1 2 Values are listed for the on axis case when the source
163. s considerably higher and more variable In order to avoid saturation the detector at these wavelengths needs to be read very rapidly which in turn leads to poorer detector cosmetics 17 NaCo User s Manual VLT MAN ESO 14200 2761 o TITT See my o8 W I i 1 I i uE iy Liiil VPN TN i i it Wo Ail 00 es Fe AlN 2 0 SMUSS gt EG T T Te A BSS Til Mi A wy Pin pny yr PAN i WW I il EN Af will IN y mi LE I i al Qoa i F M 4 0 4 2 4 4 4 6 5 0 Wavelength um Figure 3 2 Model atmospheric transmission between 1 and 5 um for a water vapour column density of 1 6 mm and at airmass 1 Lord 1992 NASA Tech Mem 103957 The standard sky subtraction technique is to use chopping and nodding Chopping is achieved by synchronizing the readout of the detector with the secondary mirror of the telescope M2 which alternates chops between two positions If the chopping is fast enough efficient subtraction of the sky can be achieved by subtracting the images taken at the alternate positions The result of a chopped image is therefore a background subtracted image with positive and negative if within the field of view of the detector objects For the NaCo the typical distance between the two positions the chop throw is 10 and the chopping frequency is typically around 0 1 Hz Usually it is essential 18
164. s of the experiment Furthermore for observational programs relying on precision calibration it is simply good practice to preserve the optical system in a stable configuration between source and reference star Although simple in principle the rotator simply has to track the elevation axis ignoring the azimuth axis in practice such a mode can be take some effort to fully implement as software driving the pointing tracking and guiding systems together with the AO system all needs to understand the implications of the new sky rotation Pupil tracking mode is the default way to observe with SAM and is implemented in transparent way for the users 5 6 3 Detector readout and cube mode setup for SAM For bright targets the dominant noise term is in the perturbations from the turbulent atmospheric phase screen Rapid readout of the detector array tends to freeze the motion of the interference fringes reducing the impact of the seeing on the measured coherence of the incoming wavefront Thus seeing drives us to read as many rapid exposure frames as possible but this needs to be traded off against detector readout noise which will rapidly dominate for fainter stars CONICA is ideally suited as a masking camera because it offers a readout mode for collecting data cubes of consecutive frames of any given integration time with minimal overheads and high duty cycle These data cubes typically consist of hundreds of short exposure 0 1sec frames for b
165. s single and without an extensive circumstellar dust shell or if binary has a relatively wide companion of at least several arcsec An attempt should be made as far as possible to preserve the same AO parameters between source and calibrator star If using the visible wavefront sensor this can present difficulties because often science targets will be very red or dusty to give resolved structure Finding calibrator stars for such extreme spectrum objects can be challenging If we consider an object such as WR 104 see imaging section below which is 14 mag in V but 2 mag in K then any normal star with similar IR fluxes will be orders of magnitude too bright for the visible WFS at the same settings For such targets it may be necessary to use the IR WFS Calibration is further enhanced by taking more rapid exposures removing the effects of seeing and irregular AO correction from the data There are compelling reasons to make multiple visits between the source and calibrator This will help to beat down the random noise and explore any systematic term in the calibration Furthermore Fourier coverage will be enhanced by the sky rotation obtained between successive visits This is helpful for imaging but even more crucial for faint companion detection The regular sampling grid on which the Fourier data is recorded permits some ambiguity when only a single snapshot is recorded Wide binaries can masquerade as much closer companions and give
166. section IIb and expressed as lt A AV gt a x b x RV with RV AV E B V 1 We set lt RV gt to 3 1 which is an average value for the interstellar medium and is essentially independent of AV for wavelength longer than 0 7um 9 5 4 Tracking table For objects with high proper motions and this usually means solar system objects the usual set of coordinates is not sufficient The user has to provide a separate tracking table giving the relative offsets between the AO reference object and the target in arcsec AO reference science target coordinates as a function of universal time UTC An example of the format of this tracking table is given in Figure 9 3 The file containing the tracking data must be edited by hand and be available on the user s local disk Checking the Tracking Table check button below the coordinates entries enables the Choose File button next to it You can then attach your file to the selected reference object and the tracking table can also be seen via the View button which is enabled as soon as the file is attached Please note that the data of the tracking table are then copied into the interface which means that you do not need to keep the original file on your disk except of course if you want to edit your data You would then have to re attach the table to the reference object If you changed your mind and do not want the tracking table anymore just deselect the Tracking Table check button 115
167. ser s Manual VLT MAN ESO 14200 2761 7 3 8 NACO img acq SAMMoveToPixel This template does a telescope preset and then sets the pupil tracking mode sending the spiders to a pre defined angle which depends on the mask being used This angle was chosen to prevent the telescope spiders from intersecting any holes The rest of the acquisition is identical to that of NACO_img_acq_MoveToPixel The template always saves the final acquisition image Table 7 8 describes the parameters of this template Table 7 8 Parameters of NACO img acg SAMMoveToPixel P2PP Label Default Values Description DIT NODEFAULT Detector Integration Time sec NDIT NODEFAULT Number of DITs Type of AO Observation LGS NGS NODEFAULT LGS or NGS observation type PSF Reference T F F Set to T if it is a PSF reference star Pupil Tracking Mode T F T Always set to T PT is compulsory RA offset arcsec 5 RA offset for sky image DEC offset arcsec 5 DEC offset for sky image Position angle on sky 0 Position angle Add Velocity Alpha 0 Additional tracking velocity in arcsec sec Add Velocity Delta 0 Additional tracking velocity in arcsec sec Filter NODEFAULT Filter name Sparse Aperture Mask NODEFAULT Neutral density Filter Full none Camera NODEFAULT Camera name NAOS Parameter file NODEFAULT NAOS aocfg file from JNPS 7 4 NaCo imaging science templates For observations with the SW filters the readout mode of the detector should be set to either Double RdRstR
168. sition 0 75 min Initial setup NAOS CONICA 2 min AO acquisition 5 10 min Depends on the brightness of the source used for AO Strehl measurement 4 min Not charged to the user Imaging acquisition 0 5 min Polarimetric acquisition 1 min Spectroscopic acquisition 1 5 min Depends on target brightness Coronographic acquisition 2 3 min Depends on target brightness SDI 4 acquisition 10 min Accurate centering is mandatory LGSF acquisition 10 min On top of the classical ACQ time Observation templates Readout overhead per DIT FowlerNsamp 2 sec Readout overhead per DIT NDIT Double 0 7 sec RdRstRd Readout overhead per DIT Uncort negligible Telescope Offsets 9 sec 1 NAOS header 7 sec 2 Stop and Start AO 2 sec 3 Start and completion overheads for IRACE 9 sec 4 1 2 3 4 typical offset 27 sec 2 4 time between frames without offsets 16 sec Change in instrument configuration 1 min HWP in or out 30 sec HWP angle setup 15 sec Rotator offset for polarimetry and SDI 1 2 min Re centering for 4QPM and SDI 4 2 min All observations using chopping 30 Add to the exposure time Night time spectroscopic flats 6 min pet on off pair Night time spectroscopic arcs 6 min Night time coronographic flats 6 min per on off pair 70 NaCo User s Manual VLT MAN ESO 14200 2761 Table 6 6 Example 1 Imaging a faint source V 15 for visual WFS or K 10
169. sition angle Offsets NODEFAULT List of rotator offsets in degrees Filter NODEFAULT Filter Name Neutral density filter Full Neutral Density filter Camera NODEFAULT Camera Name 99 NaCo User s Manual VLT MAN ESO 14200 2761 CONICA FOV S27 28 1024 1024 1024 1024 Figure 7 9 An illustration of how the NACO_pol_obs_GenericOffset template works with Number of offset positions 9 NEXPO per offset position 1 Observation Type O or S O List of offsets in X 400400400 List of offsets in Y 2 3 2 3 2 3 0 2 3 2 3 0 2 3 2 3 List of Position Angle Offsets 0 45 The dashed line connecting position 9 with 5 is the offset done after the 9th and 18th exposures Position 5 corresponds to the position the target was acquired This sequence has been designed so that the entire field of view is covered 7 7 2 NACO pol obs Retarder This template is used for imaging polarimetry without chopping exclusively with the half wave plate It can be used with all filters with the exception of J and Mp and with the Wollaston prism This templates works with defined generic offsets It must follow the acquisition template NACO img acq Polarimetry The latter must be used if the Wollaston prism will be used For each given offset position the template runs over the list of half wave plate angles before moving to the next offset position Only at the end of the OB does the telescope move back to the original position and the half
170. standards B dwarfs and solar analogs are not suitable As a consequence for this mode two telluric standard stars will be taken as part of the calibration plan One star adapted to the short wavelength calibration and one for the Lp and Mp calibration The arc lamps cannot be used to calibrate the dispersion of the prism modes At long wavelengths there ate no visible arc lines at short wavelengths the lines are severely blended One can take spectra with the NB and IB filters to define pseudo arc lines The RMS of the fit is relatively large 10 nm The fit is only good between the bluest and reddest narrow band filters currently 1 04 and 4 05 microns Beyond 4 5 microns one needs to use the telluric absorption features in the spectra of bright stars This fit is more satisfying than the fit done with pseudo arc lines and there might be a possibility of using the very broad telluric features short ward of 4 microns to use this technique over the entire 1 5 micron wavelength range However this remains to be tested Planetary nebulae do not appear to be suitable At J the resolution is too low and at M the thermal emission from the nebulae dominates Nighttime arcs and flat fields Imperfections in the slits together with instrument flexure means that day time flat fields and arcs depend on the rotator angle For this reason the template NACO_spec_cal_NightCalib allows one to take nighttime arcs and flat fields immediately after spect
171. t Pixel Size Dark Current Wavelength range Q E Aladdin 3 10261024 27 um 0 05 0 15 0 8 5 5 um 0 8 0 9 ADUs pixel The new detector is more sensitive to heavily saturated sources The limiting magnitudes that are observable are specified in Table 6 4 Please check carefully section 6 15 for tolerated saturated observations For bright objects a number of electronic and optical ghosts become apparent If the source is at pixel coordinates x y there will electronic ghosts at approximately 1024 x y 1024 x 1024 y and x 1024 y and there may be an optical ghost which looks like a set of concentric rings The ghosts can be seen in Figure 5 22 Figure 5 22 Illustration of the ghosts present on CONICA images when observing a bright object In addition to the electronic ghosts there is also an optical ghost characterised by its circular shape The 1 The dark current consists of the array dark current which is much lower than the numbers listed here and thermal radiation from the instrument 2 Although the array has 1026 rows only the first 1024 are used The last two rows do not contain useful data In most cases the exception being the cube mode images and Mp imaging frames users will receive images that have 1024 pixels in x and y For observations in the Mp the array is windowed to 512 X 514 57 NaCo User s Manual VLT MAN ESO 14200 2761 electronic noise visible on the si
172. t considering the following limitations o The AO acquisition is done on CONICA in imaging mode i e with no other dimming optical elements in the path 67 NaCo User s Manual VLT MAN ESO 14200 2761 o The need to avoid persistence on the CONICA detector These limits apply for DIT lt 1 Such bright objects heavily saturate the detector and cannot be used for science For longer DITs these limits should be increased by approximately 1 magnitude for every 10 fold increase in DIT The careful reader will note that this is not a linear relation When acquiring or when observing targets in imaging or polarimetry a saturation of a factor 4 is the maximum acceptable The saturation level is defined for each detector mode by the full well depth see Table 5 11 Any other expected saturation level for field stars should be accepted prior to observation In service mode waiver request must be submitted In visitor mode prior approval for such observation must be obtained especially if only half nights are attributed to the project The magnitude at which saturation starts depends on several parameters filters Strehl objective etc The ETC should be used to check that objects of scientific interest do not saturate the detector Moreover actual weather conditions may change this limits In particular users are warned that asking for THIN conditions is not a viable strategy given the variability of the clouds it is too risky to acqui
173. t spot it is practically impossible to normalise the response of the spot relative to the response outside it i e absolute flatfielding inside the spot is very difficult One can remove the pixel to pixel sensitivity variations by using a flat that is taken without the coronagraphic plate but this kind of flat does not remove dust features that are on the plate As of P82 a new version of the coronagraphic acquisition template for all masks supported by a glass substrate C_0 7_sep_10 4QPMs will take one flat on and one flat off images Those can be used for flat fielding of the science data taken afterwards since the mask is not moved out of the beam 5 2 10 Pipeline for coronagraphy Coronagraphic observations are not supported by the pipeline 5 3 Simultaneous Differential Imaging plus coronagraphy SDI 4 SDI 4 is a new mode of NaCo offered as of P81 April 2008 It was commissioned together with the new 4QPMs by a team from LESIA Observatoire de Paris led by A Boccaletti and collaborators J Baudrand P Riaud and P Baudoz The SDI mode of CONICA can be combined with the 4 quadrants phase mask optimized for the H band to achieve high contrast and improve the detectability of faint sub stellar companions neat bright stars ideally down to massive extra solar giant planets by reducing the photon noise at small angular separations The advantages of this new mode are o It allows deeper integration by about a factor 50 100
174. te and observe brighter targets that could saturate badly when the conditions change for the best Note also that the WFS itself cannot be allowed to saturate the penalty being the impossibility to perform AO correction Users need to restrict themselves to the magnitude limits indicated in Table 4 2 6 16 Nighttime calibrations For spectroscopic observations users can take spectroscopic flats and arcs immediately after the observation These nighttime calibrations are generally better than the ones taken in the daytime because daytime calibrations are taken with the rotator in a fixed position and a combination of instrument flexure and inhomogenities along the slit causes the image of the slit on the detector to move by a fraction of pixel when the rotator angle changes For coronographic observations with the semi transparent mask users should take nighttime flats with the NACO_coro_cal_NightCalib template These nighttime calibrations are sigificantly better than the ones taken in the daytime because daytime calibrations are taken without the mask Daytime calibrations with the mask are not useful because they are taken with the rotator at a fixed angle and a combination of irregularities on the glass plate holding the mask and instrument flexure means that flats depend on the rotator angle 6 17 Instrument and telescope overheads The execution time report produced by P2PP computes the overheads according to the rules reported in Tab
175. ted if needed in acquisition The second image is meant to be used as sky 5 3 5 Pipeline for SDI 4 SDI 4 observations are not supported by the pipeline or by the ETC 40 NaCo User s Manual VLT MAN ESO 14200 2761 5 4 Grism Spectroscopy Table 5 5 summarizes the main characteristics of the long slit spectroscopic modes A spectroscopic mode is made up of a grism an order sorting filter and an objective The mode name is the identifier given to the mode and it is used in P2PP The resolution R is computed for the 86 mas slit For slitless spectroscopy and for spectroscopy with the 172 mas slit the spectral resolution is set by the PSF SJ SH SK SHK and SL are special broad band filters for spectroscopic applications They cover a wider wavelength range than the standard J H Ks and L band filters respectively The L band filter is only offered in spectroscopy for imaging applications users should use the Lp filter Table 5 5 Spectroscopic modes The mode name consists of the objective the grism number and the order sorting filter Mode Spectral domain Order Spatial scale Linear Dispersion R microns mas pixel nm pixel 5544 SJ 0 91 1 40 1 54 2 00 400 543 SE 1 37 1 84 3 54 0 69 1500 S L3 SH 1 37 1 72 3 27 0 34 1500 27 4 SH 1 37 1 84 1 2T 0 97 500 S54_4_SHK 1 30 2 60 1 54 1 94 550 S54_2_SK 1 79 2 49 2 54 0 97 1400 S27_2_SK 1 79 2
176. ters of NACO_coro_obs_Astro P2PP Label Default Values Description NDIT img NODEFAULT Number of DITs for the imaging DIT coro NODEFAULT DIT sec for coronagraphy DIT img NODEFAULT DIT sec for imaging Readout mode Double_RdRstRd Readout mode Window Size 1024 Size of the window Store Data Cube T F F Store in data cube flag Jitter Box Width NODEFAULT Jiter box width sky only NDIT for object position NODEFAULT Number of DITs at the object pos under the mask NDIT for sky position NODEFAULT Number of DITs at the sky pos with the mask NEXPO Obj only coro NODEFAULT Number of exp with target under the mask NEXPO per offset pos NODEFAULT Number of exp per imaging position img NOFF sky only coro NODEFAULT Num of offset pos on sky with the mask NOFF img NODEFAULT Number of offset positions for imaging Offset coordinates NODEFAULT SKY or DETECTOR List of offset in X NODEFAULT Offsets in arcsec List of offset in Y NODEFAULT Offsets in arcsec Filter coro NODEFAULT Filter Name for coronagraphy Filter img NODEFAULT Filter Name for imaging Mask Position NODEFAULT Coronagraphic mask Neutral Density Filter Full Neutral Density filter Camera NODEFAULT Camera Name 7 8 3 NACO_coro_cal_NightCalib This template is used for taking nighttime flat fields and it should be placed immediately after the coronagtaphic or the SDI 4 templates If Number of Night Flats is set to n where n
177. the K band can be used with any narrow to broadband filters in the K band and respectively for the 4QPM designed for the H band Figure 5 7 Radial profiles of the PSF compared to that of the coronagraphic image obtained with the 4QPM_K left and the 4QPM_H tight 33 NaCo User s Manual VLT MAN ESO 14200 2761 900 ESTTTTTTT 7 _ FETTET LE EGNE Normalize OT ee ey ey EE VG bi ee ee ee wee e ee ee ee eee Figure 5 8 Chromaticity of the 4QPM_K measured on the 2004 mask with a fibre i e no seeing effects 5 2 6 Comparison with the classic Lyot masks Measurements were made in 2004 and are still valid for the new masks Figure 5 8 shows data obtained on a natural star The maximum attenuation is only a factor 10 with the 4QPM while it reaches typically 200 with the 0 7 Lyot therefore allowing deeper integrations However the Lyot mask is blind over an area 4 times larger than the 4QPM near the centre and that is precisely the interest of the 4QPMs 5 2 7 Observation strategy with the 4QPMs The precise centring of the science target behind the focal plane mask is critical for the success of the coronagtaphic observations and it is done interactively through an acquisition template It can also be tuned during the execution of the observing templates In general the mask centres do not coincide with the centre of the chip and the field of view can be vignetted in complex ways Both the centre and the am
178. the NACO pol obs GenericOffset see 7 7 1 template with the difference that some DPR keywords in the FITS headers of the images are set to different values allowing pipeline processing and archiving 7 8 NaCo coronagraphic science templates For SW observations the readout mode of the detector should be set to either Double_RdRstRd ot to FowlerNsamp 7 8 1 NACO coro obs Stare This template is used for coronagraphic observations and it moves the telescope alternatively between a fixed object position and a sky position The parameter Number of AB or BA cycles defines the number of times this is done but unlike the NACO_spec_obs_AutoNodOnSlhit and NACO img obs FixedSkyOffset templates the sequence is ABABAB and not ABBAAB for the example in which the Number of AB or BA cycles is set to 3 The number of exposures at the object position is defined by the Number of Exposures Object Only parameter The telescope does not offset between these exposutes The number of exposures at the sky position is defined by the Number of offset positions Sky only and the telescope can offset between these exposures The sky positions are randomly distributed around a position that is set at a constant distance defined by the parameters Sky offset in DEC and Sky offset in RA from the original telescope position and within a box whose dimensions are set by the parameter Jitter Box Width in arcsec It is strongly recommended especiall
179. to be inserted in P2PP OBs are saved The default is your home directory O Set server name this menu item raises a small pop up window that allows one to change the name of the host machine where the PS server can be accessed It is unlikely that normal users will need to use this feature If you do happen to accidentally change the name the server name can be found at http www eso org observing etc naosps doc Every change is automatically recorded in the jnpscf file located in the user s home directory Additionally depending on your local installation of the PS you may want to edit the file and modify the web enable resource enabling you to switch between the standard installation web enable true and the case where you access the PS server on your local machine web enable false However this latter case should normally never be encountered by the average user hence the default value is the correct one in most cases 121
180. ts One has to deal with high and variable backgrounds and modest detector cosmetics In general the IR background particularly at longer wavelengths is higher for an IR instrument with an AO system because of the additional optics in an AO system Additionally the classical chop and nod technique which is commonly used for the LW filters in non AO systems works less well as the DM introduces background fluctuations that do not cancel perfectly This does not degrade L band observations but it may degrade M band observations Given the relatively small field of view of CONICA it is possible to observe in the L band without having to chop and nod However the overheads are relatively large typically 50 100 as the sky has to be sampled frequently at least once a minute and poor results can be obtained if one does not offset frequently ot if the time scale for fluctuations in the L band background is short We strongly recommend that users limit themselves to the autojitter template if they choose not to use the classical chop and nod technique Users are free to choose between jittering and the more classical chop and nod style of observations for the Lp NB_3 74 and NB_4 05 filters Observations in the M band can only be done with chopping One of the major differences between AO and non AO systems is the pixel scale The pixel scale of CONICA can be as fine as 0 013 which is a factor 10 smaller than ISAAC Hence it will take 100 times l
181. tter adaptive optics performance if the active optics system of the telescope is running 61 NaCo User s Manual VLT MAN ESO 14200 2761 6 3 The influence of the moon Moonlight does not noticeably increase the background in any of the CONICA modes so there is no need to request dark or gray time for this reason However it is recommended not to observe targets closer than 30 to the moon to avoid problems linked to the telescope guiding active optics system The effect is difficult to predict and quantify as it depends on too many parameters Just changing the guide star often solves the problem Visitors are encouraged to carefully check their target positions with respect to the Moon at the time of their scheduled observations Backup targets are recommended whenever possible and users are encouraged to contact ESO in case of severe conflict i e when the distance to the Moon is smaller than 30 Visitors can use the tools that are available in http www eso org observing support html select the link airmass which is under User Support Tools to help determine the distance between targets and the moon for given dates However the moon may affect the quality of the adaptive optics correction if the source used for wavefront sensing is fainter than V 16 In these cases reducing the FLI constraint to approximately 0 7 and increasing the distance to the Moon to approximately 50 degrees is generally adequate Even here it
182. uations are generally not essential for long wavelength aperture masking One reason is that the masks themselves dramatically cut down the sky background and stellar target by a factor ranging from 84 to 96 47 NaCo User s Manual VLT MAN ESO 14200 2761 depending on the mask Furthermore thermal anisotropies in the sky tend to be smooth and slowly varying with little fine grained structure on scales of tens of milli arcsec where the interference fringes from the masking are formed 5 6 5 Choosing which mask to use The philosophy of aperture masking taken to the extreme would suggest a mask with many tiny holes each of which makes an almost point sample of the incoming wavefront Such a mask would pass very little light and be useless for all but extremely bright targets With only 4 throughput the 18Holes mask is the nearest approximation to this ideal in CONICA with the other masks having fewer but larger holes and passing increasingly more light up to a maximum of 16 for the 7Holes mask Masks with many closely spaced holes also suffer from a second problem that of bandwidth smearing Using a wide optical bandwidth filter the fringes formed between a pair of holes will occupy a range of spatial frequencies proportional to the bandwidth This can mean that power from neighbouring baselines can smear into one another confusing the signals In general this means that masks with many holes must also be used with the narrowest b
183. uators behind the DM and the rate at which WF errors can be measured processed and corrected the server loop bandwidth The performance of an AO system is also directly linked to the observing conditions The most important parameters are the seeing or more explicitly r and t the brightness of the reference source used for WFS and the distance between the reference source and the object of interest In case of good conditions and a bright nearby reference source the correction is good and the resulting point spread function PSF is very close to the diffraction limit A good correction in the K band typically corresponds to a SR larger than 30 At shorter wavelengths particularly in the J band or in the case of poor conditions or a faint distant reference source the correction is only partial the Strehl ratio may only be a few percent 15 NaCo User s Manual VLT MAN ESO 14200 2761 Observed object Y Uncorrected image ef y Plane wavefront Atmospheric turbulence Corrugated wavefront Pg Deformable mirror Tip tilt mirror e Real Time Sy Computer A A i Beam spitter Wavetron sensor Y AO corrected image Corrected wavefront Camera high resolution image Figure 3 1 Principle of Adaptive Optics 3 3 Infrared Observations with an AO system Observing in the IR with an AO system is in broad terms very similar to observing with other IR instrumen
184. uccessively fainter targets the 9 and 7 holes configurations may be used although the Fourier coverage becomes markedly worse There are two different 9 hole configurations 9holes and BB_Yholes The distinction between these two being that the simple 9holes offers superior Fourier coverage and slightly higher throughput but is not suitable for large fractional bandwidth observations For bandwidths wider than about 10 15 the Oholes mask is unsuited and the BB_9holes should be used 45 NaCo User s Manual VLT MAN ESO 14200 2761 The two dimensional layout of the holes specifies the Fourier coverage afforded by the given mask This was optimized with a computer parameter space search algorithm which follows from and extends the work of Golay 1970 JOSA 61 272 Exact locations of the holes cut for each mask together with all relevant dimensions and specifications of the physical masks themselves have been provided in the NACO_SAM web pages http www eso org sci facilities paranal instruments naco inst mask_datasheet html A scaled illustration depicting the optical effect of the masks as projected onto the correctly scaled VLT telescope pupil assuming ideal optical alignment is givenfuseful below The large circumscribed circle represents the outline of the VLT primary mirror while the smaller centered circle shows the silhouette of the secondary mirror It is important to note that the spiders which support the se
185. with respect to conventional imaging with SDI unsaturated o It allows getting closer to the central star An example flat field is shown in Figure 5 10 This mode is now completely commissioned and is offered in VM only as of P81 Please refer to the webpage http www eso org instruments naco inst sdit 4 html for additional information 36 NaCo User s Manual VLT MAN ESO 14200 2761 Figure 5 10 Flat field of the SDI 4 corrected from detector flat field taken with the H filter only not SDI filters The FoV is 8 for each quadrant 5 3 1 Contrast with SDI 4 The contrast when combining the 4QPM_H with SDI and SDI was measured The measurements were done as follows Gaussian fitting was used to determine accurately the position of the PSFs in order to measure the relative positions between the 4 images These images were extracted and re centred at the sub pixels precision using the result of the Gaussian fitting Sub images were over sampled to improve alignment if needed and to allow better spectral rescaling Images are numbered from 0 to 3 starting from the lower left corner and turning anticlockwise with Ay 1 625um 1 575um and As 1 600um We computed Ay Ax Ao As An Dy M As normalization to total intensity The results are displayed in Figure 5 11 The dotted line corresponding to the 4QPM alone is identical to Figure 5 7 except near the centre because the bandwidth is much smaller than p
186. y for very bright sources to select an area so that the main target is out of the field of view for sky measurements to avoid saturation effects The coronagraphic mask is left in the beam for the sky exposures The object positions will be observed with the AO loop closed The sky positions will be observed with the AO loop open Table 7 22 describes the parameters of this template The template provides the flexibility to adjust the number of NDIT sub integrations for the OBJECT and SKY frames NDIT for the OBJECT positions defines the number of sub integrations on the object and NDIT for the SKY positions defines the number of sub integrations on the sky The total integration time excluding overheads is defined in seconds by DIT x NDIT for the OBJECT pos x Number of Exposures Object Only NDIT for SKY positions x Number of offset positions Sky only x Number of AB cycles If Number of offset positions Sky only is set to zero the sky is not observed In this case the total integration time is DIT x NDIT for the OBJECT positions x Number of Exposures Object Only and all other parameters are ignored In this way the template takes a series of exposures of the target without offsets However sky subtraction is almost always required so this option will probably only be used in very special circumstances 102 NaCo User s Manual VLT MAN ESO 14200 2761 NACO coro obs Stare Jitter Box Width N

VERY LARGE TELESCOPE NaCo User Manual

Contents

Download Pdf Manuals

Related Search

Related Contents