LSO-MAN-ESO-90100-00..
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1. 04 04 11 SUSI2 file hbme fselman opa docu LSO MAN ESO 90100 0012 src susi oOo Annexes Filter Transmission Curves Special Broad band Filter Plot Filter Plot click for ASCII file click on thumbnail click for ASCH file click on thumbnail r 822 IB 609 830 IB 662 831 WB 490 824 WB 665 825 U 823 cae d I 12 of 14 11 30 04 04 11 SUSI2 file hbme fselman opa docu LSO MAN ESO 90100 0012 src susi He II 4880 O III 6000km 883 H beta 881 H alpha 884 O III 882 H alpha 6000km 885 Am mh mh eee Se LER Laake iunii mami sme Release History Release Date Changes and Comments 0 1 1998 First version by Sandro D Odorico and Gabriel Martin 0 2 20 Nov 1998 Added filters photometry etc O Hainautt 00000000 0 2 1 1 Dec 1998 Hints and transmission curves O Hainaut 0000000000000 0 2 2 18 Dec 98 Added note on vignetting 0000000000000 1 0 I9 Apr 99 several additions B 817 orientation corono 0000000000 LI 19 Jun 99 Added 2d throughput epoch 1 2 20 Aug 1999 Added narrow band filters 0000000000000 1 3 30 Nov 1999 fast photometry and few typos fixed 0 000000 4 31 Aug 2000 New version of the zero point and count rates 7 Feb 2001 updates 0h 1 6 25 Aug 2001 jupdates 0h 7 30 Dec 2001 updates 0h 26 Aug 1 8 2002 update mb 152. 1 Instrument Overview The NTT Nasmyth focus A hosts since 1998 two new instruments the IR imager spectrometer SOFI and the direct imaging CCD camera SUSI2 The latter is an upgrade version of the SUperb Seeing Imager identical in concept imaging at the f 11 focus of the telescope with one additional reflection but with a 4 times larger field 5 5 x 5 5 arcmin SUSI2 incorporates the first version of new ESO controller FIERA with a mosaic of two 2k x 4k 15 um pixel thinned anti reflection coated EEV CCDs Other novel features of the instrument are an 8cm x 8cm sliding curtain shutter which permits uniform exposures down to 0 3 seconds and a special cryostat designed to operate on a rotating Nasmyth adaptor SUSI2 and SOFI share the same mechanical structure attached to the Nasmyth adaptor flange and the same cable derotator The direct beam from the telescope feeds SOFI A 45 mirror is inserted in the light path when SUSI2 is in operation This manual is extensively based on the SusI 2 commissioning report and on the preliminary manual by S d Odorico and G Martin 2 Instrument properties 2 1 Optical parameters Optical Components in the Light Path The optical path of SUSI2 includes the three mirrors of the telescope the 45 reflection prism with a multi layer coating reflection efficiency gt 90 in the range 340 500 nm gt 95 in the range 500 1100nm this prims is known as Mirror 4 in the NTT jargon and the coated quartz w
3. The table below lists the mean astrometric parameters over the two chips Variable X coefficient Y coefficient 11 30 04 04 11 SUSI2 6 of 14 file home fselman opa docu LSO MAN ESO 90100 0012 src susi X POUL 00033 Y 0 Q0013 TUS XY T USUDUDO 0 00004 X2 0 00004 TOL UOURUUS Y2 0 00004 DE UD No aberrations or change of focus have been detected over the full field covered by the mosaic down to an image quality of 0 5 arcsec FWHM The chip geometry is summarized in Fig 1 with the effect of an additional Rotator Offset Susi Rotator Offsets M E ku L3 Object Instr Nig D Figure 2 Orientation of the SuSI2 detectors Rotator 2 3 Photometry and Throughputs The photometric parameters have been determined during the commissioning of the instrument and are measured regularly as part of the Maintenance Plan of the NTT Typical values for 2001 obtained using several Landolt standard fields are presented hereafter for the Bessel filters It should be noted that the zero points show a slow decrease over the past two years which 1s being investigated Obviously these values should be used only as reference careful observers will re measure them during their run This 1s specially true for the Zero Points whose values are strongly affected by the normalisation region used when preparing the flatfields Up to date values can be found at http www ls eso ore lasilla sciops ntt susi docs susiCounts
4. html Table 3 SuSI2 Photometric Calibration typical 2001 values zero points in ADUs U u 0 10 U B 23 52 B b 0 22 B V 25 46 V v 0 02 V R 25 70 k xt R r Q 05 R For the purpose of observation preparation an exposure time calculator for SUSI2 is available at this web site It computes the counts of the instrument based on the optics and CCD data as they are known now The results are in good agreement with the number of photo electrons measured at the telescope The table below gives the average measurements normalised to a star of 15 11 30 04 04 11 SUSI2 file hbme fselman opa docu LSO MAN ESO 90100 0012 src susi magnitude in one second exposure and at airmass for two epochs The stability of countrates is excellent as illustrated by the evolution curves displayed at the above web page Table 4 Count rates in adu on SUSI2 for a mag 15 star arimass 1 3 Observing with SuSI2 3 1 Generalities SuSI2 is entirely operated within the VLT observation scheme Observation Blocks are prepared the days before the observations using P2PP and executed at the telescope It 1s also possible to create copy and modify the Observations Blocks at the telescope actually the most efficient way to observe in visitor mode is to prepare in advance all your Target Packages and Observation Descriptions while preparing only models of Observing Blocks which you will duplicate and modify while o
5. Aug Most links broken Repaired FSE E E z 191 29 Aug Changed Doc No from LSO MAN ESO 40100 0002 to LSO MAN ESO 90100 0012 and 2004 archived FSE 1 10 ial Made the header ISO9000 conformant FSE 0Oo 13 of 14 11 30 04 04 11 SUSI2 file hbme fselman opa docu LSO MAN ESO 90100 0012 src susi C i bad oe eid UF SEARCH HELF HEUS 14 of 14 11 30 04 04 11
6. ME images with dithering offsets SUSI img obs DoubleW Reads two non overlapping subwindows for fast photometry Calibration Templates ISUSI img cal Dark SCTOI Biases and Darks SUSI img cal DomeFF SCTO2 Dome flat fields request a series of flat at a given level Twilight flat fields request a series of flat at a given leve computed taking into account a model of the sky brightness de increase ISUSI img cal TelFocus SCTO04 Through focus sequence SUSI img cal SkyFF SCTO3 3 2 Hints This section lists a collection of hints and tips for observing with SuSI2 At this point it is not ordered in a very coherent way Central gap Remember that there is a 8 gap between both chips that the optical axis 1 e the reference for pointing if in CCD 46 left very close to the gap and that NTT points very well If you just preset to the coordinates of a star your object can fall into the gap You can either add subtract 1 2 arcsec to the RA of the star beware of the cos dec or start your sequence with an offset e g in a SUSI img obs Jittertemplate 2 As the space between the CCD is masked the central gap can be used as a crude coronograph to mask a bright star To accurately point an object in the gap use the SUSI img acq MoveTobPixel acquisition template Standard stars Although both chips are very similar you may want to photometrically calibrate them separately if a very accurate calibration is re
7. SUSI2 1 of 14 0 Introduction 1 Instrument overview 2 Instrument Properties 2 1 Optical Parameters file home fselman opa docu LSO MAN ESO 90100 0012 srce susi European Southern Observatory La Silla Observatory La Silla SciOps SUSD Superb Seeing Imager 2 Direct CCD Imaging Camera at the NTT User s manual Doc No LSO MAN ESO 90100 0012 Issue 1 10 November 29 2004 Keywords SUSI2 Manual NTT Prepared M M Billeres M Billres 2002 August O Hainaut Hainaut O Hamaut 2002 August C LEN O Hainaut 2002 August see table at the end for minor releases Table of content 11 30 04 04 11 SUSI2 file home fselman opa docu LSO MAN ESO 90100 0012 srce susi 2 2 CCDs 2 3 Photometry and Throughputs 3 Observing with SUSI2 3 1 Generalities 3 2 Hints Annexes Filter Transmission curves 2 of 14 0 Introduction This manual describes the SuSI2 instrument on the ESO New Technology Telescope at La Silla Observatory It is meant for the observers preparing observations on that instrument or processing data produced with SuSI2 The manual exists only in HTML The on line version has many in line links to other pages Nevertheless a printed version from this document will contain all the relevant information links that point to critical information are given in clear in the text the others are for general or background information
8. ailable anymore SS WB 490 824 502 72 7 32 510 0 87 5 ELS WB 665 825 665 67 123 52 679 0 974 boo U 823 368 97 low pass 339 0 81 0 Atmospheric CCD cut off at small an transmission at 1 370nm He II 880 469 53 7 644 4 469 0 P22 e SOS HBeta 881 486 438 6 608 4855 832 o O II 882 500 984 7 244 500 0 aM ZZ O III Cont 883 511 061 7 019 510 5 84 2 O I 6000km s H alpha 884 655 528 6 976 656 5 895 rr 4 pm 6 68 655 6 899 669 0 90 3 H alpha 6000km s Notes on the filters It was though for a while that Filter B 811 was causing an elongation of the image in case of very good seeing This could not be confirmed indeed B 811 gives images of excellent quality Filters IB 609 and IB 662 are not available anymore Additional information incl transmission plots are available in Annex A or on the La silla Instrumentation web page ar http filters ls eso org efs or from the team Remark the very high peak transmission of these filters up to twice that of similar filters 1n EMMI Because of their extremely high costs we do not plan to purchase any additional filters If you need currently unavailable filters you can send us Is imaging 2 eso org a request with 11 30 04 04 11 SUSI2 file hbme fselman opa docu LSO MAN ESO 90100 0012 src susi a scientific justification However be aware that 1t 1s unlikely that we have funds to acquire the filters Spe
9. allel each through a single port at 2 x 10 pixels sec There are three binning options unbinned 1x1 2 x 2 and 3 x 3 and the possibility of defining a single read out window which can overlap with both chips The read out times intervals from the closure of the shutter to the display of the image in the Real Time Display monitor are 56 16 and 9 seconds for the three binning options respectively On the RTD the default options show North at the top and West chip 45 to the left The measured read out noise are 4 7 e for 45 and 4 6 e for 46 For the latest measurements of the CCD parameters pls check the NTT detector page at http www ls eso org lasilla sciops ntt CCDs CCDs html on the WWW updated weekly This page also links to an history of these parameters evolution CCD QE Measurements of the Qes for the two chips in the ESO detector laboratory show that 45 is up to 5 relatively more efficient than 46 The table below gives the average values Table 2 SuSI2 s CCDs quantum efficiency nm 350 400 500 600 700 800 900 1000 Saturation and Linearity Pixel saturation occurs at 150000 e With the adopted gain of 2 25 e ADU this corresponds 4 of 14 11 30 04 04 11 SUSI2 5 of 14 file home fselman opa docu LSO MAN ESO 90100 0012 srce susi approximately to the full rang e of the ADC converter in the unbinned mode The CCDs have been found linear within 0 15 over the fu
10. bserving If the last sentence does not make any sense to you don t dispair your support scientist will introduce you to P2PP You may also want to read the P2PP User s Manual a complete detailed reference document The instrument templates describing the different possible observations calibration and target acquisition are operationally identical to those which have been used with the previous SUSI imager and are described in details in the SuSID EMMI Template Signature File Parameters Reference Guide A short summary is given in the table below Curious readers can consult the EMMI user manual for a longer description of the VLT observation scheme at the NTT Note that as of Period 68 Oct 2001 a new set of SuSI2 observations templates has been introduced known as SuSI2001 As of Period 69 April 2002 the old templates are not supported anymore and new OBs must be prepared using SuSI2001 7 of 14 11 30 04 04 11 SUSI2 8 of 14 file home fselman opa docu LSO MAN ESO 90100 0012 srce susi Table 5 SuSI2001 Templates MN Template with old template Description Acquisition Templates SUSI img acq Preset Sm Opp ETE 00 loop blind pointing M E EE at location brings the object SUSI img acq MoveToPixel SATO2 to a given pixel after taking a short I nmm image Observation Observation Templates Te _img_obs_Exposure Som sige image ISUSI img obs Ji itter Sem VU ME
11. check that the object is well centered Adjust the start values of the window and retest 1f needed e modify the number of exposures to the number requested eg 500 and start Additionally another template SUSI img obs DoubleW has been introduced to perform fast photometry of two objects e g a variable star and a reference star using two non overlapping windows Proceed as above to define the two sub windows To decrease the read out time between two exposures you can use the 2x2 mode or even better the 3x3 1f you look for short variations in photometry you are not really interested by the resolution but by the minimisation of the dead time Example of light curve obtain with this method ECOSZ17T 3814 10 EM t M os P z i E A a X phap DnE A A A Po COE i aa E P i a 74 CU amp d at 5 rs n EM P r4 H mE 4 Etg j e Vic ia 5 w o7 p p 4 E IOUE AH DOO A000 S000 Seconds Figure 5 Example of photometric light curve of variable star with SUSI2 in mmag Vignetting and M4 coating until Nov 1999 the lowest part of the CCDs 500pix was slightly vignetted by M4 this region should not be used for accurate photometry It was also discovered in Jul 1999 that the coating of M4 was damaged resulting in a slightly higher diffusion Both problems were solved in Nov 1999 by the replacement of M4 which is now well aligned For further assistance feel free to contact us at Is imaging eso org 11 30
12. cial filters can be mounted in SuSI upon request with advance notice The filters must respect the following specifications 2 Diameter lt 100mm a Thickness lt 10mm Filters with a dimeter lt 100mm must be mounted in an adaptor We have a set of such adaptors for some standard diameters and we can manufacture adaptors for other diameters It is critical to organize this in advance Be warned that it is very likely that special filters will have a different optical thickness than the standard filters causing a focus offset that will have to be measured and cause some additional overhead during the observations 2 2 CCDs The two EEV CCD 44 80 were the first in the large format with 2 x 4 k 15u pixels in operation for astronomy Their properties when operated with the FIERA controller are summarized below Data Format Read out Time and Read out Noise The two EEV chips are identified as ESO CCD 45 and 46 The two frames are combined in a single FITS file chip 45 has lower x values 1 e on the left on standard display the space between the two chips has been filled with some overscan columns so that the respective geometry of the two chips is approximatively preserved The format of the file is 4288 x 4096 Along the x axis there are 50 prescan 2048 active 46 overscan pixels for chip 45 followed by 50 prescan 2048 active and 46 overscan for chip 46 There is one single read out option in which the two chips are read in par
13. do an offset along the y axis For a small number of exposures a tilted grid gives good results For larger number of exposures consider taking the exposures moving the telescope on a star like pattern all the positions falling on a circle typical radius 15 or even better taking the offsets at random within a disk of 15 radius If your object is very large consider moving the object from chip to chip after each exposure as one would nod the telescope for Infra Red observations Fringes in I Images obtained in the I filter present some strong fringes caused by the interferences of night sky lines in the thin CCDs As the flat fields are obtained with white light they do not correct these fringes Moreover the fringes correspond to an additive pattern and should therefore be subtracted and not divided To correct them the fringe pattern has to be extrated from the scientific images themselves The following procedure gives very good results it should be however noted that as the flatfielding of the frames the corrections of the fringes can be performed in several different ways This procedure is the simplest that gives good results Obtain the observations with a large dithering pattern be sure to have at least 5 long exposures in I ideally at least 5 per field Subtract the bias from all frames Normalize the sky level of all your I exposures to the average sky level you may want to work field by field Store t
14. he exposure time and 3 adjust for the difference of the intensity level For the latter you can take as first approximation the ratio of the mean level of the science image by the mean level of the fringing pattern and multiply the fringing pattern by this factor Then subtract this corrected fringing pattern to your images It looks not too bad see the Figure 3 for an example but if you want to do precise photometry you have to do fine tuning and adjust the factor for each image It 1s possible to define sequences of many windowed frames in order to sample the lightcurve of a rapidly varying object 11 30 04 04 11 SUSI2 11 of 14 file home fselman opa docu LSO MAN ESO 90100 0012 srce susi Figure 5 Example of window For example the window presented above has a size of 100 x 400 pixels The mean dead time between two images is 13 s with an exposure time of 10 00 s in the 3x3 mode so a sampling time of 23s To use this mode use the following procedure e acquisition template SUSI_img_acq_Preset blind acquisition e atest exposure with full frame and bin 1x1 SUSI_img_obs_Jitter with an offset to move the object of interest out of the gap e Once this image is displayed measure the position of the object of interest x y in pix on the RTD and define the read out window in a SUSI img obs Jitter template window TRUE Start x 50 y 50 size 100 400 number of exposures 1 e excute that template and
15. he normalization factor for further use Median average all the I exposures again you may want to work field by field the result should contain no object just the fringes and the flat field structure a Divide the result by the twilight I flat you are left with a flat sky and the fringes which have also been divided by the flatfield which they should not This will be corrected later Get the average sky level and subtract it you want to have an image with a mean Zero you are left with the flatfielded fringes alone Multiply the result by the flatfield this is your master fringes template For each image multiply the master fringe template by the normalization factor you used for that image Subtract the result from the original image a Divide the defringed frames by the twighlight I flat 11 30 04 04 11 SUSI2 10 of 14 file home fselman opa docu LSO MAN ESO 90100 001 2 src susi Figure 3 Left Panel Dirty image in I Right panel Clean image in I Figure 4 The fringing pattern You can retrieve the fits file corresponding to a classical fringing pattern click on the Figure 4 We built it with 34 1mages in I The exposure time of all the images is 600s If you don t want to build your own fringing pattern and we recommend that you build your own pattern you can use this one but take care to 1 flat field it with your sky flat the pattern raw fits 1s not flatfielded 2 adjust for t
16. indow of the cryostat transmission gt 97 over the range 340 1100 nm The filter wheel and the shutter are located in the f 11 between the prism and the cryostat Before Nov 1999 there was a small vignetted region at the bottom the the CCDs 500pix While the vignetting was flat fielded out this region should not be used for accurate photometry The vignetting was caused by the mirror 4 whose position has been adjusted 11 30 04 04 11 SUSI2 3 of 14 file home fselman opa docu LSO MAN ESO 90100 0012 srce susi Filters The filter wheel has 6 positions The filters have a diameter of 100 mm The filters currently available are listed in the table below Filter ID ae WHM wavel Bessel U 810 357 08 Bessel B 811 421 20 Table 1 un uS D filters ransm Red leak and remarks 09 EE N N 2 ua ON 417 4 0 01 1100nm 0 02 1200nm spare 0 01 1100nm 0 02 1200nm 0 06 1100nm 158 89 597 0 86 9 0 04 1200nm 0 13 1100nm 1126 0 08 2 Atmospheric CCD cut off at large wavel Bessel B 817 421 17 9 17 4 NO D ON NO m Bessel V 812 544 17 115 17 5 641 58 794 96 840 90 pass r 822 B 609 830 609 38 T m FE _ fo Zoli 260 a QUEE o METH ES z not measured Use at your own risk Not available anymore AIEDEEE flue skal not measured Use at your own risk JINI illii bkn B 662 831 66229 354 6650 Not av
17. ll range 0 60000 ADUs Charge Transfer Efficiency Both serial and horizontal CTE are better than 0 999999 CCD dark current 0 5 e pix hour i e negligible for all practical purposes Bias Level To be derived from the average of prescan and overscan regions of each frame because of a slight dependence on the mean level of the charge in each row of the CCD Osec bias exposure average at 300adu again check the NTT detector web page for up to date values Figure 1 Example of SUSI bias the difference of sensibility bewteen the two CCDs 1s responsible for the contrast Cosmetics Chip 45 left present 15 bad columns while 46 has some blemishes that look quite bad but actually flat field out very well Image scale Field Size Image Quality The scale at the Nasmyth focus of the NTT is 5 4 arcsec mm The measured pixel scale is 0 085 arcsec pixel 0 161 arc sec in the 2 x 2 binned mode Each chip of the 2x1 mosaic covers a field of 5 5 x 2 7 arcmin The gap between the chips corresponds to 100 real CCD pixels or 8 arcsec In the default position of the rotator the gap runs in the N S direction The optical axis which is also the reference for pointing is at about 60 pix left of the center of the mosaic i e in chip 45 left very close to the inter CCD gap The angular misalignment between the two chips is smaller than 6 arcmin Very accurate astrometry requires an independent calibration of the two subfields
18. quired An efficient way to do so is to observe each standard field through all your filters then rotate the rotator by 180deg and do the same sequence again In that way all the stars that were on one chip during the first sequence will fall on the other chip for the second sequence ensuring that both are calibrated exactly in the same way The rotation takes 20sec In practice you can define an 11 30 04 04 11 SUSI2 9 of 14 file home fselman opa docu LSO MAN ESO 90100 0012 srce susi OD with your standard exposures and link it in two different OBs one with a 0 rotator offset in the aquisition template SUSI img acq Preset the second with a 180 offset The p2pp impex stdcal directory of the NTT machines both off and on line contain a set of pre defined OBs for selected Landold fields for standard read out modes and for 0 and 180deg rotation Jitter and super flatfield To obtain a very good flat field it 1s criticalto use the super flat technique introduced by Tyson developped by Tyson Lilly and others which consists in utilizing the scientific images themselves as flatfield In order to do so the telescope should be moved jittered between each exposure The size of that jitter should be of the order of 2x the largest object in the field The jitter pattern should be chosen depending on the total number of exposures on each field remembering that there 1s a vertical gap between the chips 1 e never
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