Home

HIGH SPEED PHOTOMETER INSTRUMENT HANDBOOK

1. F 26 1 2 3 4 2H 1 2 3 4 J 4 2200 Lt Op o O o O lo o O y lo 1 ES E 0 4 B 1 0 B 0 4 A 1 0 A 1 0 A 0 4 A 1 0 B 0 4 B 4 3 2000 1 E lrgaw F240W ER 4 2008 E E Dt pp Da 4 F o F145U1 D c B A F220U1 A B c D 25 E 1800 EE 1 2 3 4 oF 1 2 3 4 4 A 1800 E gb O o O o o o o 73 4 E E 0 4 B 1 0 B 0 4 A 1 0 A 1 0 A 0 4 A 1 0 B 0 4 B 4 J 1600 4 ay 1600 FF F145M F220W Ea 4 E 5 pp FI3sul F E D c F152U1 A B c D 25 4 14005 Ke 3 5 2 i ab A 3 E a E 1400 Eo6 o O o O o o O o 6 4 0 0 4 B 1 0 B 0 4 A 1 0 A 1 0 A 0 4 A 1 0 B 0 4 B 4 2 1200 E 7 F195W F152M EE 4 1000 g F135U1 B A F248U1 A B 33 1000 E F 2a 3 1 2B 3 1 1 E L 90 o O O o 9 4 800 E 0 4 C 1 0 C 1 0 C 0 4 C 4 800 E 10 Flera5w F248M 510 800 e 11 gl goo E a belle ul eb ubububububububuhububehubububububul dg Eo E 12 11 10 9 8 7 6 5 4 3 2 1 0 1 2 3 4 5 6 7 8 9 10 11 12 J E mm E 200 200 6 Editada ada ata e tada alada lala Pte 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 3200 3400 3600 3800 4000 Deflection steps 50 45 40 35 30 25 20 15 10 5 0 5 10 15 20 25 30 35 40 45 50 Arc seconds V3 IDT2 UV1 Proposal names Chart version 1 4 11 10 90 Jeffrey W Percival V2 Version 2 0 10 HSP Instrument Handbook Figure 2 6 UV2 IDT Apertures and Filters 0 200 400 600 800 1000 1200
2. Very bright sources will have to be measured using analog current data format because their counting rates will be too high for the pulse counting electronics The statistics of noise for the current data format will be determined by the counting rate the time constant of the current amplifier and the sample time The noise will consequently be somewhat more complicated than simple Poisson statistics Only when the number of photons counted is very large gt 10 will other sources of noise become noticeable One such noise source is the imperfect guiding of the HST pointing system Guiding errors move the source away from the center of the aperture decreasing the fraction of the source s flux that reaches the HSP detector Spatial variations in the quantum efficiency of the photocathodes may also lead to small variations in the count rate as the image of the star moves The spherical aberration increases the effect of the former putting more energy at the edge of the aperture and decreases the latter by smearing the light out over a larger piece of the photocathode The fluctuations can be large 5 over an orbit and vary from pointing to pointing Fluctuations in the high voltage can change the gain of the photomultiplier sections of the IDTs This will have little effect on the pulse counting rate but may change the current out of the tube The HSP high voltage power supplies have been designed so fluctuations will lead to IDT current v
3. 0 01 POL Bialkali 0 05 0 01 PMT GaAs 400 200 UVI CsTe 0 05 0 05 UV2 CsTe 0 1 0 1 Table 4 6 Sky Background Counting Rates for 1 Apertures Filter Detector Sky cts s Remarks F240W VIS UV 0 008 without prism F240W VIS 0 005 with prism F248M UV 0 004 F262M VIS UV 0 005 F284M UV 0 005 F320N VIS 0 015 IDT PMT beamsplitter F355M VIS 0 019 u F419N VIS 0 044 v F450W VIS 0 61 B F551W VIS 0 26 V without prism F551W VIS 0 13 V with prism F620W VIS 0 63 R F750W PMT 2 6 IDT PMT beamsplitter F140LP UV 0 031 Crystal Quartz F160LP VIS 2 3 Suprasil F160LP POL 0 46 Suprasil F160LP UV 0 030 Suprasil F400LP VIS 1 9 GG 395 NOTES 1 The sky brightness is modeled as a dilute 4700 K black body distribution with m5556 22 7 magnitudes per square arcsecond see Faint Object Spec trograph Instrument Handbook 2 Sky counting rates for filters at and near Lyman a F122M F135W F145M are strongly affected by the geocoronal La line which varies greatly depend ing on the position in orbit and the viewing angle 3 For all other filters not listed the counting rate from the sky is expected to be smaller than the dark count rate from the detector lt 0 002 cts s for VIS POL and lt 0 006 cts s for UV1 UV2 30 HSP Instrument Handbook Table 4 7 Target Acquisition Time minutes UV1 UV2 IDTs Effective Temperature my 5000 K 10000 K 20000 K 40000 K 15 4 0 4 0 2 0 2 16 10 0 6 0
4. 2 4 0 1 2 3 4 5 6 7 8 9 10 11 12 13 E 0 Ela la ll ada dy 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 3200 3400 3600 3800 4000 Deflection steps 50 45 40 35 30 25 20 15 10 5 0 5 10 15 20 25 30 35 40 45 50 Arc seconds V3 IDT3 VIS Proposal names Chart version 1 4 11 10 90 Jeffrey W Percival v2 HSP Instrument Handbook Version 2 0 Figure 2 5 UVI IDT Apertures and Filters 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 3200 3400 3600 3800 4000 ERP AAA ANI URN NOI DELI DIRI DARI 4000 4000 Eo 12 11 10 9 8 7 6 5 4 3 2 1 0 1 2 3 4 5 6 7 8 9 10 1 12 4 ES Dana E ES DELI una ON UN DARE RALE UN Rana DERE ERE RUDE RARE RA RARE RARA LN DLE 1 380 4 3800 Bo ail 11 4 3600 49 E F122U1 D B A CLRU1 F 10 3600 de E 29M 1 2 3 2L 5 7 4 m 90 o o O o 49 2f T E 0 4 B 0 4 A 1 0 A 0 4 E 4 Soret E 8 rro lg 4 3200 3200 7 _ F248U1 F E D c D B A 7 E E E l k 1 2 3 4 1 2 3 4 3 3000 6 O o O oD3 gt o O 6 3000 E L 0 4 B 1 0 B 0 4 A 1 0 A 0 4 C 0 4 D 1 0 C 4 E 2800 gt E F248M F140LP 35 3 2800 Eo 4 HH F218U1 D Cc B A F278U1 A B G D 44 F Pal 1 2 3 4 2J 1 2 3 4 4 2600 3 i o o o o x o SI 2600 E L 0 4 B 1 0 B 0 4 A 1 0 A 1 0 A 0 4 A 1 0 B 0 4 B 4 2a00 2 I F218M F278N S 2400 TRE a ca F184U1 D Cc B A F240U1 A B Cc D 41 2200
5. It is impossible to say at this time what the accuracy of the standard calibrations will be but ultimately the goal will be to remove all systematic effects larger than 0 1 of the signal Smaller effects will probably always be the responsibility of the observer and larger effects will almost certainly be present during the year following launch 44 HSP Instrument Handbook Version 2 0 Chapter 6 Bibliography White R L 1989 HSP Target Acquisition Handbook Description of the various target acquisition strategies using the HSP Bless R C 1982 The High Speed Photometer for the Space Telescope in The Space Telescope Observatory ed D Hall NASA A general overview of the HSP from which much of Chapter 2 was taken White R L 1983 Effect of Guiding Errors on Scientific Performance of HST Instruments STScI Instrument Science Report GEN 001 Describes how pointing jitter affects the science data for all the HST instruments Phillips W 1984 System Controller User s Manual University of Wisconsin Describes the in ternal electronics of the HSP in gory detail including a section on how to program the Bus Director White R L 1984 Timing Considerations for HSP Data Collection STScI Instrument Science Report HSP 001 Technical description of the constraints on collecting continuous data with the HSP 1990 Call for HST Observing Proposals Space Telescope Science Institute General information about
6. STAR SKY mode For STAR SKY mode the sample times for the star and the sky can be set independently using the SAMPLE TIME and SKY SAMPLE optional parameters The minimum time required for the image dissector beam to be deflected from one location to another is 10 milliseconds Should measurements of the star s brightness be required at intervals shorter than that two alternatives are available either background exposures can be taken before and after the high speed data run requiring three SINGLE mode exposures two on the sky and one on the star or if a second dissector contains a filter identical with or relatable to the filter used for the program star two dissectors can collect data simultaneously one from the star one from the sky also STAR SKY mode but with the two different detectors specified in the configuration as HSP D1 D3 In this mode the sample times for each detector must be identical but can be as short as 28 us This is slightly more than twice the shortest possible sample time 10 7 us when only one detector is collecting data In principle this sample time could be reduced by using a special bus director program see 3 1 1 The SPLIT configuration in which a beamsplitter sends part of a star s light to two different detectors uses the same technique as two detector STAR SKY mode to get simultaneous measure ments of a star in two colors On the other hand two color photometry using the PRISM mode is a
7. The centering is improved by doing the acquisition twice in a row This double acquisition is now embedded in the scheduling software so that two are performed for every one requested Do not request two consecutive acquisitions on the exposure log sheet unless you want four to be performed If the star field is simple so that the program star is easily identifiable the target may be suitable for an Onboard target acquisition Software in the HST computer examines the pseudo image and makes a list of up to 20 targets within a specified brightness range The program star can be specified to be the only candidate on the list in which case it is an error if there is more than one candidate or the n th brightest star on the list where n is 1 2 etc The centroid location of the selected star is then found automatically and the correct telescope offset to the desired filter aperture is calculated This offset is passed to the HST pointing control system and the small maneuver is carried out The program star is now in the correct aperture with the detector parameters properly set and the observation begins If the program star is in a crowded field or is highly variable it may not be possible to acquire it by means of the automatic finding routine described above Instead an Interactive or Early target acquisition is necessary In an Interactive acquisition the pseudo image is displayed on the ground where the observer indicates the target with a curso
8. These latch outputs are used to control focus and deflection amplifiers high voltage power supplies discriminator thresholds analog gain settings etc A 1 024 MHz clock signal received through the I O port supplies a signal to the A D converter and synchronizes sampling start and stop control signals to the two pulse counters It can also be used as a test input to the counters The outputs of the two pulse counters the A D converter and the eight one byte latches are multiplexed and transmitted through the detector controller bus I O port to the system controller As its name implies the system controller s functions have to do with the instrument as a whole rather than with a specific detector These functions include serial command decoding and distribution detector controller programming science data acquisition and formatting serial digital engineering data acquisition and formatting and interfacing with the HST command and data handling system through redundant remote modules and redundant science data interfaces The system controller consists of an Intel 8080 microprocessor memory and various I O ports Direct memory access is provided to allow rapid data transfer through the science and engineering data ports and to allow science data acquired from the detector controllers to be stored in memory quickly An 8K byte ROM block is provided for the microprocessor program storage The remaining memory is composed of six 4K blocks of RAM
9. Version 2 0 Figure 4 9 HSP PMT Beamsplitter Characteristics Figure 4 10 HSP Polarizer Characteristics 35 36 HSP Instrument Handbook Figure 4 11 Reflectivity of HST and HSP Mirrors Figure 4 12 Time to Reach V 15 with S N 100 UV Filters Version 2 0 HSP Instrument Handbook Version 2 0 Figure 4 13 Time to Reach V 15 with S N 100 UV VIS Filters 1 Figure 4 14 Time to Reach V 15 with S N 100 UV VIS Filters 2 37 38 HSP Instrument Handbook Figure 4 15 Time to Reach V 15 with S N 100 Polarimetry Filters Figure 4 16 Time to Reach V 15 with S N 100 Beamsplitter Filters Version 2 0 HSP Instrument Handbook Version 2 0 39 Figure 4 17 Time to Reach V 15 with S N 100 Longpass Filters 4 2 Planning a Typical Observation with the HSP This section shows how to calculate exposure times etc using the information given above and in Chapter 3 The example has a relatively simple goal but it demonstrates some of the complications that can arise in planning an observation and shows that the considerations discussed in Chapter 3 are often important 4 2 1 How to Calculate Exposure Times The exposure time which must be specified on the exposure logsheet is the total time HST spends pointing at the target from the beginning to the end of the observation The exact relation between the exposure time t and the other times sample time delay time etc specified for the observations depends on the mode u
10. accuracy requires the merging of several data sources not typically available to observers so interested parties should contact the HSP team for details 3 3 Sources of Noise and Systematic Errors There are many sources of noise and or possible systematic errors for the HSP This section discusses those that are currently judged to be of possible significance 3 3 1 Noise Noise is here taken to mean random variations in the measured counting rates that would average to zero in a long series of observations The noise in most HSP observations will be determined by the Poisson statistics for the star sky and detector dark counts The star counting rate obviously depends on the color and magnitude of the star and on the filter used The sky counting rate has the same dependencies it also depends in a complicated way on the angle to the sun the moon and the limb of the earth Dark counts in the HSP may be produced either by emission of thermal electrons from the photocathode 0 1 counts sec for the IDTs 200 counts sec for the PMT or by impacts of high energy particles on the photocathode and the first dynode Large particle fluxes like those encountered in the South Atlantic Anomaly may also cause the MgFs in the HSP filters and faceplates to fluoresce for a period of time The particle background and its effect on the HSP will vary with the position of the HST in its orbit This effect is small and has yet to be quantified for the HSP
11. beam and baseplate the main structural elements of the HSP The box beam runs the length of the instrument thereby connecting the two forward and aft fittings and carries the pre load The baseplate actually a milled out lattice structure is attached to the box beam and provides stiffness to the structure Four internal bulkheads on each side of the box beam and baseplate form ten bays for the electronic boxes which are mounted on 16 HSP Instrument Handbook Version 2 0 the baseplate In addition to giving mechanical support to the electronics and to the wire harness the baseplate provides a high conductance path between electronic modules as well as a radiating surface The optics and detectors are mounted to but thermally isolated from the box beam on the side opposite the baseplate and at the forward end of the instrument Detectors are not actively cooled and are expected to range in temperature between 15 C and 0 C for cold and hot orbits respectively Over an orbit their temperatures will change by no more than 0 1 C and will change by no more than 8 C during an extended observation 2 5 Observing with the HSP 2 5 1 Target Acquisition An observation with the HSP begins with the acquisition of the target As for most of the other HST instruments the HSP has four target acquisition strategies Blind Onboard Interactive and Early These schemes are described in detail in the HSP Target Acquisition Handbook this
12. details 3 1 2 Standard Data Formats There are five standard data formats and a default for HSP data They are Table 3 1 HSP Data Formats Format Description Restrictions BYTE one byte digital Ct lt 256 cts C lt 2 x 10 cts s WORD two byte digital Ct lt 65 536 cts C lt 2 x 10 cts s LONGWORD three byte digital Ct lt 16 777 216 cts C lt 2 x 10 cts s ANALOG 12 bit analog C gt 10 cts s in two bytes ALL three byte digital C gt 10 cts s plus two byte analog DEF Default Format selected by STScI Here C is the count rate from the target and t is the sample time for the observation specified by optional parameter SAMPLE TIME Chapter 2 distinguishes only between digital and analog data formats because it will often be unnecessary for the observer to specify which particular format is to be used In that case the sixth entry in the table DEF is selected by default on the observing forms then the data format is set to the STScI default for the source s counting rate as specified by the flux data in the target list and integration time The brightness of the source determines HSP Instrument Handbook Version 2 0 21 whether pulses can be counted or whether the IDT current must be measured if the count rate is low enough for pulse counting the sample time determines whether one two or three bytes of digital output will be necessary The shorter digital formats BYTE and WORD are used to reduce the data
13. from the target passes through a filter in this case clear suprasil Fig 2 4 and on through a 1 arcsecond aperture after which it strikes a Ag Cryolite beamsplitter at 45 to the incident beam The mirror reflects red light to the photomultiplier PMT via a red glass filter and a Fabry lens The beamsplitter passes a spectral band in the blue on to a relay mirror and to the VIS image dissector Truly simultaneous observations can therefore be made at about 7500 A and 3200 A The PMT detector and the F320N filter on the VIS detector can also be used independently for single color photometry 2 2 1 However there is ordinarily no advantage in doing so because taking data through both filters requires no additional observing time or overhead Note that the 45 reflection in both the PMT beamsplitter and the prism beamsplitters intro duces significant instrumental polarization in the transmitted beam so that the count rates for a 10 polarized source will vary by about 2 with the HST roll angle 2 2 4 Polarimetry In the HSP POL configuration light from the target passes through a filter aperture assembly which is only about 4 arcminutes off axis directly to the image dissector no relay mirror is used The filter assembly Figure 2 7 contains four near UV filters see Table 4 2 across which are four strips of 3M Polacoat with polarizing axes oriented at 0 45 90 and 135 The aperture plate contains a single aperture for each fi
14. la E i 142 11 10 9 8 7 6 5 4 3 2 1 0 1 2 3 4 5 6 7 8 9 10 1 12 3 200 mm 4 o Ets ladrar APE rel Cae ere nel Bn IP Derr da 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 3200 3400 3600 3800 4000 Deflection steps oe Re ee e e e 50 45 40 35 30 25 20 15 10 5 0 5 10 15 20 25 30 35 40 45 50 Arc seconds IDT4 UV2 Proposal names V3 Chart version 1 6 11 10 90 Jeffrey W Percival V2 4000 3800 3600 3400 3200 3000 2800 2600 2400 2200 2000 1800 1600 1400 1200 1000 800 600 400 200 HSP Instrument Handbook Version 2 0 Figure 2 7 Polarimetry IDT POL Apertures and Filters 12 11 10 9 8 7 6 5 4 3 2 1 0 1 2 3 4 5 6 7 8 9 10 11 12 12 NIN RE DARA DELA BARE ARG MERA ERE RARE DURA DUNN ARA ES RARE RANE RULE NN UNE ERE MLN 12 We aad 10 E 10 E 0 300 600 900 1200 1500 1800 2100 2400 2700 3000 3300 3600 3900 J 9 l 4000 E TETTI LALA ML RA ARA RARI REA TA MARA giza DI MARA RARI NADA RIA BAL AAA ee RS NOA RSA BARS RARA RIA hisa kiad Mia 3 4000 dg 8 3800 CLRP A c 3800 4 8 E E 1A 1 3 J z 3600F 5 ES 1 3600 Ai E 3400 0 65 C 0 65 D 3 3400 J 6 F 76 E E F160LP 4 E 3200 E 3 S 3200 5 H E F327P 0 90 135 45 4 5 F 3000 18 1 2 oD 3 4 3000 I 45 E O O O O 4 74 E 2800 E POLO POL90 POL135 POL45 2800 1 30 2606 F327M 2600 48 20 E F277P 0 90 135 45 4 que E 240
15. proposed as targets of opportunity 2 5 4 Other Useful Information The 10 Hz data collection rate in which a data word is 8 bits long rather than the usual 16 would fill the HSP buffers in only 0 16 s However data at this rate can be transferred continuously to the on board tape recorder for about 10 minutes where it will be stored until its contents are transmitted to the ground More details on the transmission and storage of data are given in Chapter 3 The HSP contains no calibration lamps its final radiometric calibration will be established by observing stars with known spectral energy distributions The instrument s sensitivity can be HSP Instrument Handbook Version 2 0 19 estimated from the specification that in 2400 seconds it be able to measure a 24th magnitude star in the B band with a signal to noise ratio of 10 Typical image dissector dark counts and currents are less than 0 1 sec and 1 pA respectively Chapter 4 gives a detailed description of the HSP sensitivity 20 HSP Instrument Handbook Version 2 0 Chapter 3 Details of the HSP HST System Chapter 2 describes the general characteristics of the HSP in enough detail for most observ ing programs However sometimes more information will be needed in order to use the HSP as efficiently as possible This chapter has sections on some internal details of the HSP s operation on some quirks and limitations of the HSP HST system and on sources of noise in measurement
16. require that the data be equally spaced However another consequence of the HST s low orbit is that data from the HSP often will not be equally spaced in time The light travel time from one side of the HST orbit to the other is about 40 msec Consequently observations that have sample times shorter than this and that last a significant fraction of an orbit will not be equally spaced in the heliocentric rest frame The STSDAS system at STScI will provide software to calculate the time of each sample in the solar rest frame see the timeseries package in STSDAS however the observer should be prepared to analyze the resulting unevenly spaced data Consult the STSDAS Users Guide for more information 3 2 4 Absolute Timing of Observations Although the HSP can make observations with sample times as short as 10 7 usec the absolute time of an observation can only be established to within a few milliseconds This happens because the phase of the HST onboard clock is only known to a few milliseconds compared to the time on the ground The HST clock is calibrated daily with regressions performed to establish clock rates and clock drift rates Observations of the Crab pulsar have been performed and comparisons to ground based radio observations show that the HST clock is well within the 10 msec specification and is probably good to within a millisecond of UTC Reducing HSP data to absolute time at this HSP Instrument Handbook Version 2 0 23 level of
17. the HST observatory 1990 Hubble Space Telescope Phase IT Proposal Instructions Space Telescope Science Institute Detailed information about how to fill out the exposure logsheets target lists etc properly Ford H C 1985 Faint Object Spectrograph Instrument Handbook Space Telescope Science In stitute Includes some information that may be useful for estimating the signal to noise for HSP observations e g references for spectral energy distributions and tables of interstellar reddening Percival J W 1989 High Speed Photometer Flight Software Reference Manual University of Wisconsin Details on the operation of the on board software including target acquisition and thermal control Percival J W 1989 High Speed Photometer Flight Bus Director Programmer s Manual University of Wisconsin How to create special photometry programs to be loaded into the HSP data collection processor Percival J W 1990 High Speed Photometer SMS Compiler and Analyzer Tools University of Wisconsin A user s and programmer s description ofthe HSP SMS tools A must for command validation instrument usage analysis and for producing concise readable summaries of HSP activity Percival J W 1991 High Speed Photometer Flight SMS Pipeline University of Wisconsin How to get Science Mission Schedules SMS from the STScI and analyze them for HSP commanding 1991 STSDAS Users Guide Space Telescope Science Institute 19
18. the observer Digital format data can be taken with sample times as short as 10 7 us Pulses separated by about 40 ns or more can be separately detected so that count rates of up to 2 5 x 10 Hz can be accommodated with a dead time correction of no more For a detailed description of data format selections see 83 1 2 14 HSP Instrument Handbook Figure 2 8 HSP Electronics Block Diagram Version 2 0 HSP Instrument Handbook Version 2 0 15 than one percent The sample times for both digital and analog data formats are commandable in 1 ys intervals up to 16 384 s Between successive samples there can be a delay time of zero to 16 s again in 1 ys steps This delay time will usually be set to zero except in cases where a delay is necessary for some reason e g in l detector STAR SKY mode see below Use optional parameters SAMPLE TIME and DELAY TIME to specify these values on the exposure logsheet By default the sample time is 1 second and the delay time is its minimum possible value The five identical detector controllers perform those functions that relate to a specific detector i e they receive a sequence of parameters and instructions from the system controller necessary for an observation and science data collection Each contains an I O port a storage latch two 24 bit pulse counters and a multiplexer Detector parameters are received from the system controller through the I O port and are stored in eight one byte latches
19. which may be configured in any order 4K of the RAM are allocated for the microprocessor system 16K as a buffer for science data storage and 4K as a spare block The spare block may be used to replace any other 4K block that becomes defective In contrast to the detector controllers the system controller is dual standby redundant The power converter and distribution system converts the input 28V DC bus power from the HST to secondary DC outputs required by all other subsystems and provides power input switching and load switching for independent operation of individual detector electronics and heaters The DC DC converters essential to overall instrument operation are dual standby redundant Converters that power electronics associated with only one detector are not redundant With three detectors and their electronics on simultaneously the power consumption is about 135 W 2 4 Mechanical Structure and Thermal Characteristics The HSP is aligned and supported in the HST at three registration points Two of these one forward and one aft have ball in socket fittings and the third point in the forward bulkhead provides tangential rotational restraint The mechanical loads including a pre load to keep the HSP in alignment are transmitted from the instrument to the telescope structure through the three registration points The two ball in socket fittings the electronics boxes and the optical and detector system are all mounted directly to a box
20. 0 0 32 F750W 7500 1600 2 7 28 HSP Instrument Handbook Version 2 0 Table 4 4 Locations of HSP Filters Filter IDT Name ___ Name UVI UV2 VIS POL Substrate Remarks F122M 1 1 MegF Lyman a F135W 2 MgF F145M 1 2 MegF F152M 1 1 Crystal Quartz F179M 1 Suprasil F184W 1 1 1 Suprasil F216M 1 Suprasil F218M 1 1 Suprasil F220W 1 Suprasil F237M 1 Suprasil F240W 1 2 Suprasil F248M 2 1 Suprasil F262M 1 1 Suprasil F277M 1 Suprasil F278N 1 1 WG 280 F284M 1 Suprasil F327M 1 WG 280 F355M 1 WG 280 u F419N 1 GG 395 v F450W 1 BG 28 B F551W 2 GG 395 V F620W 1 RG 610 R red cutoff from IDT F140LP 1 1 Crystal quartz Clear F160LP 1 3 1 Suprasil Clear PMT window F400LP 1 GG 395 Clear F320N 1 PMT beamsplitter VIS F750W 1 RG 695 PMT beamsplitter PMT red cutoff from PMT NOTES 1 Numbers in IDT columns indicate how many slots are occupied by the filter on that IDT 2 Locations are also given in Figures 2 4 through 2 7 3 All substrates are 1 16 inch thick 4 All substrates are coated to produce multi layer interference filters except for F450W B F620W R F750W PMT and those indicated to be clear 5 For several filters marked Cutoff from IDT one edge of the wavelength response is determined by the cutoff of the photocathode response HSP Instrument Handbook Version 2 0 29 Table 4 5 HSP Detectors Detector PhotocathodeDark Count Rate cts s 0 C 15 C VIS Bialkali 0 03
21. 0 F le 7 3 ji 2400 E 1 F 2200 O o o 3 2200 St E E POLO POL90 POL135 POL45 4 I o fF 20005 2000 0 L 3 F277M D o D2 E J ae 1800 F237P 0 90 135 45 1800 1 m F 1D 1 2 3 4 q J Poi 1600 gt 5 o ES E 3 1600 ans SETTA POLO POL90 POL135 POL45 34400 A 1 E F237M E J 1200 1200 ae E F216P 0 90 135 45 4 rice F 1000 E 1E 1 2 3 4 1000 I 5 F E O O le le 4 25 F 800 E POLO POL90 POL135 POL45 800 1 6 E 4 756 E 600 E F216M o D4 600 J TITO d0 4400 gal 8 20 3 200 18 9E 0 Eur lebe but babe bubutebubtebulububulubutel Li 0 9 E 0 300 600 900 1200 1500 1800 2100 2400 2700 3000 3300 3600 3900 I 10 10 E Deflection steps 4 11 F st y a dl ia ti ae ha Pala 12 11 10 9 8 7 6 5 4 3 2 1 0 1 2 3 4 5 6 7 8 9 10 11 12 mm AMO OOO O O TO A I A TO I TOA TO TI TOI TY TOGO 45 40 35 30 25 20 15 10 5 0 5 10 15 20 25 30 35 40 45 50 Arc seconds IDT1 POL Proposal names Chart version 1 5 11 10 90 Jeffrey W Percival V2 V3 50 11 12 HSP Instrument Handbook Version 2 0 Only one pair of filters on each of the three photometry IDTs can be used with a prism Table 4 3 lists the three pairs of prism filters Duplicates of all prism filters are also available as normal straight through filters without the intervening prism The prism mode is still being calibrated Contact the STScI for the current status of the prism mode 2 2 3 Two Color Photometry with the PMT In the SPLIT mode light
22. 1400 1600 1800 2000 2200 2400 2600 2800 3000 3200 3400 3600 3800 4000 AAA AAA AAA AAA TAD MADA ANA NEIL NI DADA ENAA NENA NAAA LINA ANAS AEA MAAA VU ANNE AAA EAA EAA DAAN HEE 4000 E 12 11 10 9 8 7 6 5 4 3 2 0 1 2 3 4 5 6 7 8 9 10 11 12 4 3800 E nee porrpro 12 q 300 11 qu d 10 F122U2 D B A CLRU2 F 10 3400 4M 1 2 3 4L 5 I 9 E o o O o do 1 E 0 4 B 0 4 A 1 0 A 0 4 E 4 si 3200 8 F122M 8 E 7 F145U2 F E D c D B A 7 4 3000 4K 1 2 3 4 aP3 1 2 3 4 4 E 6 o O o O o o O 46 4 E 0 4 B 1 0 B 0 4 A 1 0 A 0 4 C 0 4 D 1 0 C J 2800 g Ale E F145M F140LP 1 E 2600 4 F284U2 D Cc B A F152U2 A B Cc D 4 A E Al 1 2 3 4 AJ 1 2 3 4 4 3 o O o O O o O o 3 24005 0 4 B 1 0 B 0 4 A 1 0 A 1 0 A 0 4 A 1 0 B 0 4 B 4 E 2 F284M F152M zia 4 2200 1 F278U2 p c B A F248U2 A B c D 1 4 F F 4G 1 2 3 4 4H 1 2 3 4 4 E E 0 o o O lo o lo o 0 E 2000 0 4 B 1 0 B 0 4 A 1 0 A 1 0 A 0 4 A 1 0 B 0 4 B 4 Poli F278N o Piasm DES 4 18005 2 F160U2 p c B A F218U2 A B C D 2 2 E 4E 1 2 3 4 4F 1 2 3 4 a 4 1600 3 o O o O O 5 O 3 Za 4 E 0 4 B 1 0 B 0 4 A 1 0 A 1 0 A 0 4 A 1 0 B 0 4 B 4 E E Fieo F218M A 7 14001 J E 5 F179U2 D Cc B A F184U2 A B Cc D 5 4 E 4c 1 2 3 4 4D 1 2 3 4 4 5 1200 6 o O o O o o o o 6 E 0 4 B 1 0 B 0 4 A 1 0 A 1 0 A 0 4 A 1 0 B 0 4 B 4 4 took 7 F179M F184W Ze E E 8 F145U2 B A F262U2 A B SS 4 3 4A 1 3 4B 1 3 7 q sope ye O O 3 ER 4 E 0 4 C 1 0 C 1 0 C 0 4 C 4 4 soo fF 10 F145M F262M qu Po 4 11 3 400 E 4 Y SG als
23. 2 2 HSP Focal Plane Layout one of three holes in its forward bulkhead These holes are all centered on an arc 8 1 arcminutes off axis the focal plane layout for the HSP is shown in Figure 2 2 After passing through a filter which is about 36 mm in front of the HST focal plane and an aperture which is in the HST focal plane the light is brought to a refocus on the dissector photocathode by a relay mirror a 60 mm diameter off axis ellipsoid located about 800 mm behind the HST focal surface The relay mirrors enable a more efficient use to be made of the HST focal plane available to the HSP than would otherwise be possible 1 e the image dissectors are too large to place more than two directly in the focal plane The magnification of the relay mirrors is about 0 65 which converts the f 24 bundle entering the HSP to f 15 6 at the photocathode with a corresponding change in scale from 3 58 arcseconds mm to 5 54 arcseconds mm The only unusual feature of the HSP s optical system is its filter aperture mechanism see Figures 2 3 through 2 7 mounted behind each forward bulkhead entrance hole Each filter plate contains thirteen filters mounted in two columns positioned 36 mm ahead of the HST focal plane At this location the converging bundle of light from the HST is 1 5 mm in diameter well within the 3 mm width of each filter however because the light bundle is out of focus small variations in filter transmission with position should n
24. 3 0 2 17 25 1 4 0 4 0 3 18 70 3 5 0 8 0 4 19 8 1 6 0 8 20 20 4 1 8 21 50 10 5 22 25 11 23 70 30 24 75 VIS IDT Effective Temperature my 5000 K 10000 K 20000 K 40000 K 15 0 3 0 2 0 2 0 2 16 0 4 0 3 0 2 0 2 17 0 6 0 4 0 3 0 3 18 1 2 0 7 0 4 0 4 19 3 1 6 0 8 0 6 20 9 4 2 1 2 21 30 12 5 3 22 40 15 9 23 50 25 24 POL IDT Effective Temperature my 5000 K 10000 K 20000 K 40000 K 15 0 2 0 2 0 2 0 2 16 0 3 0 3 0 2 0 2 17 0 6 0 4 0 3 0 3 18 1 1 0 7 0 4 0 4 19 3 1 4 0 8 0 5 20 7 4 1 7 1 1 21 20 9 4 3 22 60 25 11 7 23 90 30 20 24 60 Version 2 0 NOTES 1 Time was calculated for a 20 x 20 image with a signal to noise ratio of 6 for the target including noise from the sky background and dark counts 2 An overhead of 25 ms per point is included 10 s for the 20 x 20 image 3 Times longer than 100 minutes are marked HSP Instrument Handbook Version 2 0 Figure 4 1 HSP Filters 1000 2500 A Figure 4 2 HSP Filters 2000 3500 A 31 32 HSP Instrument Handbook Figure 4 3 HSP Filters 2500 7500 A Figure 4 4 HSP Filters Polarimetry Version 2 0 HSP Instrument Handbook Version 2 0 Figure 4 5 HSP Beamsplitter Filters Throughput Figure 4 6 HSP Longpass Filters 33 34 HSP Instrument Handbook Figure 4 7 HSP Detector Quantum Efficiencies Figure 4 8 HSP Prism Beamsplitter Characteristics Version 2 0 HSP Instrument Handbook
25. 91 STSDAS Calibration Guide Space Telescope Science Institute 6 1 Further Reading Several resources deserve a little further description Science Mission Schedules contain the HSP commanding Each instrument team put together procedures for decoding the dense SMS files but many were based on a syntactical attack scanning for well known lexical features in the SMS The HSP team produced a program that attacks the SMS semantically It is a real compiler HSP Instrument Handbook Version 2 0 45 produced using modern compiler production tools that is capable of logically dismantling any SMS that conforms to ICD 11 A full HST data model is maintained by this program allowing the user to follow SMS directed interactions between any HST subsystems This tool produces readable digests of HSP activity including data collection summaries error reports guide star usage and even sky maps showing the HST movements for a given week In addition a post processing tool called optime produces an accurate accounting of HSP hardware usage Total on time number of cycles and so on are extracted from past SMS files The HSP team keeps online the complete history of SMS files allowing the user probably the instrument engineer to obtain quickly the flight history of any given component in the HSP Another resource is the Bus Director Compiler The HSP data collection processor is pro grammable Standard data collection programs such as Single Color Photome
26. E mode The sample time should be somewhat shorter than a millisecond to make the rebinning of the data into 1 msec bins easier see 3 2 3 0 5 msec is a good choice because then the data rate will be about 16 kilobits per sec which is comfortably under the 32 kbs rate at which the tape recorder stores data see 3 2 2 There is no way to get the data rate under 4 kbs There will inevitably be gaps in the time coverage due to occultations by the earth 3 2 2 but the period of the Crab pulsar is so well known that the gaps should not pose any data analysis problems If there are unexpected problems the pulsar is bright enough to determine the phase of a short segment of data from the data itself Finally it is necessary to specify how the target will be acquired It is possible to use the Onboard target acquisition method in which an HSP image is automatically analyzed to identify and locate the target 2 5 1 Remember that the points in an HSP image are accumulated one at a time so a target that varies during the target acquisition data collection may be misidentified or missed entirely The Crab pulsar s period is about 33 ms so we want the sample time for each pixel in the image to be a lot longer than this We chose 750 ms The total target acquisition time for the Crab Pulsar including the 25 ms per point overhead is then 400 x 25 750 ms 5 minutes 42 HSP Instrument Handbook Version 2 0 Chapter 5 Standard Calibration
27. F750_F320 x 12 3600 Es E 3N 1 1 1 t11 O a Sa s4oo F FS20N FZ50W 19 A 43400 pio E F400V D B A CLRV J 310 4 Ee 3M 1 2 3 3L 5 4 4 32003 g 2 o y Hg 3200 POE 0 4 B 0 4 A 1 0 A 0 4 E 4 E 300048 F F400LP D3 38 _4 3000 E7 F620V D c B A H F E Ag 2800 F 3K 1 2 3 A 1 2 3 12800 t6 E o O o O o o O 6 4 FF 0 4 B 1 0 B 0 4 A 1 0 A 0 4 C 0 4 D 1 0 C 4 4 2600 5 f F620W F160LP 35 2600 La m F551V F E D c F419V A B c D S 8 2400 3l 1 2 3 4 3J 1 2 3 4 4 2400 E3 E x Q o O o o o o 33 3 aes 0 4 B 1 0 B 0 4 A 1 0 A 1 0 A 0 4 A 1 0 B 0 4 B a 1 2200 F 2 2200 p2 F F551W F419N 4 Fi m F450V D G B A F355V A B C D 31 J 2000 50 3G 1 2 3 4 3H 1 2 3 4 4 e000 Mo O o O 1 O o O y oD Jo 4 1800 0 4 B 1 0 B 0 4 A 1 0 A 1 0 A 0 4 A 1 0 B 0 4 B 4 3 1800 EE F450W F355M ae 16002 E FI84V p B A F160V A B c D 2 4 1600 F E 3E 1 2 3 4 3F 1 2 3 4 4 J 1 3 O o O O o O o Js 3 1400 0 4 B 1 0 B 0 4 A 1 0 A 1 0 A 0 4 A 1 0 B 0 4 B 5 1400 Ee f F184W F160LP ld a 120015 F240V F E D c F262V A B c D ga 3 1200 FCE 3C 1 2 3 4 3D 1 2 3 4 4 E P 6 HE o o O O o O o 6 El A E 0 4 B 1 0 B 0 4 A 1 0 A 1 0 A 0 4 A 1 0 B 0 4 B 4 q 1000 PERA o D4 Sii F F240W F262M E 800 Hp 800 H 8 F240V B A F551V A B 8 4 Pop 3A 1 3 3B 1 3 1 3 600 H9 o O O o 3 9 600 Ey ae 0 4 C 1 0 C 1 0 C 0 4 C 4 4 a0 EP E F240W F551W e Ay Ett E 1 4 200 a ads lara VO A as LS AOP DOO OO era 200 F42 12 4 E 13 12 11 10 9 8 7 6 5 4 3
28. HIGH SPEED PHOTOMETER INSTRUMENT HANDBOOK Version 3 0 April 1992 Robert C Bless Jeffrey W Percival University of Wisconsin 475 N Charter Street Madison WI 53706 Lisa E Walter Richard L White Space Telescope Science Institute 3700 San Martin Drive Baltimore MD 21218 HSP Instrument Handbook Version 2 0 1 Chapter 1 Introduction 1 1 How to Use This Manual This manual is a guide for astronomers who intend to use the High Speed Photometer HSP one of the scientific instruments onboard the Hubble Space Telescope HST All the information needed for ordinary uses of the HSP is contained in this manual including 1 an overview of the instrument Chapter 2 2 a detailed description of some details of the HSP HST system that may be important for some observations Chapter 3 3 tables and figures describing the sensitivity and limitations of the HSP Chapter 4 4 how to go about planning an observation with the HSP Chapter 4 and 5 a description of the standard calibrations to be applied to HSP data and the resulting data products Chapter 5 An HSP neophyte should begin by reading Chapters 2 and 4 to get an overview of the in strument and what it can do Chapter 4 also shows how to plan an observation using the HSP Chapter 5 describes the data products received by the observer Skimming through Chapter 3 will give some feeling for the complications that may arise The HSP sophisticate will refer
29. MT Beamsplitter Characteristics HSP Polarizer Characteristics Reflectivity of HST and HSP Mirrors Time to Reach V 15 with S N 100 Time to Reach V 15 with S N 100 Time to Reach V 15 with S N 100 Time to Reach V 15 with S N 100 Time to Reach V 15 with S N 100 Time to Reach V 15 with S N 100 UV Filters UV VIS Filters 1 UV VIS Filters 2 Polarimetry Filters Beamsplitter Filters Longpass Filters Version 2 0 20 26 27 27 28 29 29 30
30. W 4500 1400 65 1 4 B F551W 5510 850 38 0 54 V F620W 6200 1300 0 72 R F750W 7000 9000 2 1 PMT beamsplitter PMT F140LP 1400 3000 90 1 7 F160LP3 1600 3000 90 1 7 UV2 IDT 1600 7000 90 2 0 VIS IDT 1600 7000 90 1 8 POL IDT F400LP 4000 7000 90 1 8 NOTES 1 Shape of F320N is determined by band passed by PMT beamsplitter rather than by focal plane filter Transmission is for beamsplitter bandpass 2 Shapes of R filter F620W and PMT filter F750W are defined by the photocathode efficiency so transmissions for filters alone are not given 3 F160LP occurs on both CsTe and Bialkali IDTs The red cutoff is determined by the photo cathode response in both cases 4 Unless listed separately filters that occur on two or three different IDTs have same throughput on all IDTs HSP Instrument Handbook Version 2 0 27 Table 4 2 HSP Polarimetry Filters Name A FWHM Transmission Throughput A A F216M 2160 300 34 0 028 F237M 2370 280 35 0 054 F277M 2770 340 38 0 14 F327M 3270 410 31 0 11 NOTE All filters on polarimeter are available with 4 polarizers oriented at 45 intervals On the observing forms these are specified as POLO POL45 POL90 and POL135 Table 4 3 HSP Beamsplitter Filters IDT Name A FWHM Throughput A A UV1 Prism F135W 1350 230 0 009 F248M 2480 370 0 1 UV Prism l F145M 1450 200 0 02 F262M 2620 290 0 1 VIS Prism l F240W 2400 550 0 62 F551W 5510 850 V 0 27 PMT l F320N 3200 10
31. andard Calibrations and Data Products 5 1 Pipeline Calibrations 5 2 Data Products 5 3 Special Calibrations Chapter 6 Bibliography 6 1 Further Reading 2 NN rm mr Table 1 1 Table 2 1 Table 3 1 Table 4 1 Table 4 2 Table 4 3 Table 4 4 Table 4 5 Table 4 6 Table 4 7 Figure 2 1 Figure 2 2 Figure 2 3 Figure 2 4 Figure 2 5 Figure 2 6 Figure 2 7 Figure 2 8 Figure 4 1 Figure 4 2 Figure 4 3 Figure 4 4 Figure 4 5 Figure 4 6 Figure 4 7 Figure 4 8 Figure 4 9 Figure 4 10 Figure 4 11 Figure 4 12 Figure 4 13 Figure 4 14 Figure 4 15 Figure 4 16 Figure 4 17 HSP Instrument Handbook Tables Acronyms HSP Configurations and Modes HSP Data Formats HSP Photometry Filters HSP Polarimetry Filters HSP Beamsplitter Filters Locations of HSP Filters HSP Detectors Sky Background Counting Rates for I Apertures Target Acquisition Time minutes Figures HSP Optics and Detectors HSP Focal Plane Layout HSP Filter Aperture Tube Configuration VIS IDT Apertures and Filters UV1 IDT Apertures and Filters UV2 IDT Apertures and Filters Polarimetry IDT POL Apertures and Filters HSP Electronics Block Diagram HSP Filters 1000 2500 A HSP Filters 2000 3500 A HSP Filters 2500 7500 A HSP Filters Polarimetry HSP Beamsplitter Filters Throughput HSP Longpass Filters HSP Detector Quantum Efficiencies HSP Prism Beamsplitter Characteristics HSP P
32. ariations smaller than 0 1 Fluctuations in the low voltages could also affect the performance of the HSP by changing the deflections and focus of the IDTs the threshold of the pulse amplitude discriminator the output voltage of the current to voltage converter etc However all of these effects have been found to be negligibly small in laboratory testing 3 3 2 Systematic Errors The accuracy of the measured brightness will be determined for many sources by systematic errors which do not average to zero after many measurements The sizes of systematic errors are inherently more difficult to determine from observations than are noise amplitudes this problem is made even harder by the fact that the HSP is capable of making more accurate measurements than any ground based photometer consequently the systematic errors of the HSP photometric system probably will not be measurable by comparison to observations using other instruments It 24 HSP Instrument Handbook Version 2 0 is hoped that the sum of all systematic errors that cannot be removed will be less than 1 of the signal Small scale spatial variations in the filters and photocathodes cause errors in the measured fluxes because the calibration targets and program targets may not be placed in exactly the same locations within any given aperture These errors should not be large because the beam is not in focus at the filters and the photocathodes are quite uniform on small scales The degr
33. ccomplished using the equivalent of one detector STAR SKY mode switching the beam of a single IDT between the two apertures associated with a particular prism Thus prism mode measure ments are not truly simultaneous but are separated by at least 10 milliseconds just as are all one detector STAR SKY measurements 2 5 3 Occultation Observations with the HSP The HSP has many advantages over ground based telescopes for occultation observations 1 Shorter sample times allow greater resolution 2 UV observations and smaller apertures greatly reduce the scattered light from the occulting body 3 Stationary occultations occur when the motion of HST nearly compensates for the motion of the occulting body The most difficult part of planning an occultation observation is probably calculating which occultations are favorable for observations with the HST The STScI can supply orbital elements to those who would like to do occultation predictions however STScI will not be able to do such predictions for GOs Another difficulty is that atmospheric drag causes the orbit to change on relatively short time scales making it difficult to predict the location of HST accurately more than a short time about a month in advance This means that it will often be impossible to determine at the time of proposal whether the HST will be suitably placed to observe a particular candidate occultation As a result many occultation observations will have to be
34. ee to which target positioning is reproducible depends on the performance of the HST pointing control system which is still experiencing some repeatability and stability problems Non linearities in the A D conversion may limit the accuracy of analog current mode mea surements Because the A D converter has 12 bits even a perfect device cannot measure the current to an accuracy better than 0 03 Fluctuations from guiding errors discussed above with reference to noise can also produce systematic errors It is likely that the guiding errors will be different for objects with different guide stars Consequently two objects with identical fluxes may have different average counting rates the one with larger guiding errors will appear to have a smaller flux It may be possible to remove this effect by analyzing the engineering telemetry from the HST to determine how large the guiding errors were for a particular observation Recent observations with the HSP show an unexplained variation in stellar flux whose period matches that of the HST orbit An orbital variation has appeared in observations with one other instrument This is an area being actively investigated and the user should contact the STScI for information on this effect The IDTs inside the HSP must warm up for some time before they can be used for accurate photometry This warm up time will be a function of the accuracy that is desired for example a few seconds will probably suffice fo
35. ement of the sky background is required it usually can be made through the other 1 0 arcsecond aperture on the same filter Apertures in a given row are 15 arcseconds apart so generally the other aperture should be suitably located for a background measurement The HST pointing need not be changed the dissector simply is commanded to collect photoelectrons from the point on the photocathode corresponding to the selected sky aperture This section discusses the various operating modes that can be used for sky subtraction with the HSP See 82 2 for a list of which modes can be used with the various HSP configurations The HST Phase II Proposal Instructions give the precise format that must be used The HSP will most commonly be used in SINGLE mode in which an exposure consists of a series of measurements of the star s brightness made through some filter aperture combination Multi color photometry is simply a series of SINGLE exposures Measurements of the sky brightness can also be made as SINGLE exposures requiring a separate line on the Exposure Logsheet The FOC will not be used as often as the WF PC because its field of view is only twice the diameter of the HSP finding apertures 18 HSP Instrument Handbook Version 2 0 If the background brightness is expected to vary significantly during the exposure then the HSP can be commanded to measure alternately the star brightness and the sky brightness from 2 different apertures on the same IDT
36. ened spectrum of the Crab pulsar in the UV is approximately V 0 5 2H 1 105 a Wm Hz F 5x 1072 or 1 5 Fy 1 5 x 10714 en z erg cm s7 3000A e g see Pulsars by Manchester and Taylor The extinction to the Crab pulsar is Ay 1 6 from the standard interstellar reddening curve tabulated in the Faint Object Spectrograph Instrument Handbook we can calculate the reddened flux at the wavelengths of the filters we are going to use Then the counting rate in each filter can be estimated from the data for the polarimetry filters given in Table 4 2 Filter A Ay Py FWHM Throughput Count Rate A mag photons em 2s 1471 cts s F240W 2400 4 07 6 0 x 107 550 0 17 8 2 F278N 2780 3 12 1 3 x 1074 140 0 39 1 3 F355M 3550 2 45 2 2 x 1074 310 0 29 7 7 F140LP 2000 4 51 4 4 x 107 1200 0 29 25 The counting rate is the product of the photon flux density the collecting area of HST 0 867 120 cm the FWHM of the filter and the throughput of the system This includes the 14 loss of light due to the secondary mirror HSP Instrument Handbook Version 2 0 41 For comparison the HSP simulator predicted a time averaged count rate of 55 per second for the F140LP UV2 filter and the actual observation yielded 43 counts per second The sky brightness is relatively small compared to the brightness of the Crab pulsar so we will not bother to measure or subtract the sky background This means that we will use SINGL
37. ent to integrate less than 30 seconds between filter changes because then most of the HST time will be spent slewing from filter to filter instead of collecting photons For two filters on different IDTs the slew time is about 60 seconds so the exposure times through each filter must be even longer for efficient use of HST time If a program requires multicolor observations at shorter intervals a pair of filters that is accessible through one of the beamsplitters must be used Table 4 3 3 2 2 Limits to the Length of Uninterrupted Observations It will often be difficult or impossible to acquire an uninterrupted series of integrations lasting more than about 30 minutes The Call for Proposals discusses HST s orbital constraints The HST will be in a low orbit so that almost half of the sky is occulted by the earth Thus most objects will be unobservable for about half of each orbit and each orbit requires only 95 minutes Furthermore it will not be possible to point HST closer than 50 from the sun and the sky background will be high when looking at a target close to the earth s bright limb Data are transmitted from HST to the ground or stored on the onboard tape recorder at either 4 x 10 or 1 024 x 10 bits sec 4 kbs or 1 Mbs There is also an internal 32 kbs link to the tape recorder The data rate from the HSP R is determined by the sample time t and the number of bits per sample n R n t The data rate from HST to the grou
38. epending on the color of the star the time to acquire a 20 x 20 HSP image may become prohibitive Then it becomes necessary to adopt a somewhat different target acquisition strategy There are several possibilities 1 Use the WF PC discussed above 2 Reduce the size of the HSP image For example a 10 x 10 image will still usually be large enough to include the target but requires only 1 4 the time of a 20 x 20 image 3 Choose a brighter star nearby for offset pointing For offset target acqui sition the bright offset star is acquired using any of the usual techniques including Onboard acquisition then the telescope is slewed to place the position corresponding to the real target in the desired aperture The brightness of the target and the availability of offset stars will determine which of these tech niques will be best for a particular target Proper motion of the target must be specified or removed when filling in the coordinates in the target list Proper motion is particularly important for 1 solar system targets that are moving rapidly 2 Blind acquisitions in which the target either has not been previously observed or in which the target has moved significantly since the last observation or 3 targets acquired via offset pointing In any case target motions of less than about 0 1 arcseconds during the course of a series of exposures are not important for HSP observations 2 5 2 Sky Subtraction Modes If a measur
39. ere the readbeam is deflected for collection of dark counts The innermost scale is the physical scale in millimeters of the filters and apertures referenced to the image dissector tube faceplate The deflection step scale represents the magnetic deflection in HSP D A units required to point the read beam to any location These are provided as reference only and are not used in proposals The outermost scale is in arcseconds and is referenced to the focal plane The V2 and V3 axes are shown relative to the position of the detectors as projected through the optics onto the sky The order of the scales for the POL diagram Figure 2 7 is slightly different All of the UV filters are multi layer interference filters of Al and MgF evaporated on MgF substrates for the far ultraviolet or on suprasil for the near UV The visual filters consist of Ag and cryolite layers deposited on glass The substrates are 1 16 inch 0 002 inch thick The general filter characteristics are listed below in Tables 4 1 and 4 2 Some filters are common to two or more photometry image dissectors for the sake of redundancy and to enable all three channels to be tied together photometrically Some filters define bandpasses similar to those flown on previous space observatories while others are similar to some in the Wide Field and Faint Object Cameras There is one filter on the POL IDT F160LP see Fig 2 7 with two 0 65 arcsecond apertures that can be used for photometry The
40. from the target count rate C see Table 3 1 a R lt 4 kbs no limit on observing time b 4 lt R lt 32 kbs observations may be up to 8 hours long if data are stored on onboard tape recorder c 32 kbs lt R lt 1 Mbs observations may usually last only 10 20 minutes depending on the availability of the 1 Mbs TDRSS link to the ground All of these restrictions mean that most observations that require more than 20 or 30 minutes will probably have gaps in their time coverage These gaps will obviously lead to some difficulties in the data analysis e g aliases of the 95 minute orbital period will show up in periodic analyses Observers should try to anticipate how these problems will affect their projects if gaps in the data will make it impossible to achieve the goal of the program they should be sure to ask for continuous observations in the proposal For some programs it may be necessary to choose targets in the continuous viewing zones small regions near the orbital poles that are visible throughout the orbit because they are not occulted by the earth Note that the continuous viewing zones are always near the limb of the earth so sky subtraction may be more critical for such observations than for targets far from the limb 3 2 3 Unequally Spaced Data Most high speed photometrists are accustomed to using mathematical tools such as fast Fourier transforms and autocorrelation functions to analyze their data these tools
41. g Zone Digital to Analog Fine Guidance System Faint Object Camera Faint Object Spectrograph Goddard Space Flight Center Goddard High Resolution Spectrograph High Speed Photometer Hubble Space Telescope Image Dissector Tube National Aeronautics and Space Administration NASA Standard Spacecraft Computer Optical Detector Subsystem Optical Telescope Assembly Pulse Amplitude Discriminator Project Data Base Photomultiplier Tube Random Access Memory Read Only Memory System Controller User s Manual Science Operations Ground System Space Telescope Science Institute Science Data Analysis System Target Acquisition and Verification To Be Determined Tracking and Data Relay Satellite System Ultraviolet Wide Field Planetary Camera 1 3 Acknowledgements The High Speed Photometer was designed and built at the University of Wisconsin by Robert C Bless Principal Investigator with scientific guidance from the HSP Investigation Definition Team Joseph F Dolan James L Elliott Edward L Robinson and Wayne van Citters Among those making major contributions to the design construction and testing of the HSP were Evan Richards Jeff Percival Fred Best Dave Birdsall Gene Buchholtz Scott Ellington Don Finegan Ed Hatter Sally Laurent Muehleisen Matt Nelson Bill Phillips Jerry Sitzman Mark Slovak Colleen Towns ley Andrea Tuffli Mark Werner Doug Whiteley and others to whom I apologize for their omission from this lis
42. h instrument is best for their proposal 2 2 5 Images with the HSP The light paths for the IMAGE and ACQ modes are identical to those for the other HSP modes These modes differ from ordinary photometry only because the data are collected in a different sequence An Image sometimes called an Area Scan is a series of integrations in which the IDT beam is moved to cover a rectangular grid on the photocathode The number and separations of the rows and columns and the sample time at each point are all adjustable The number of HSP Instrument Handbook Version 2 0 13 samples taken at each point in the image and the delay time between samples are also adjustable using optional parameters on the Phase II observing forms Targets are located in the 10 arcsecond finding aperture by commanding the HSP to take an image covering the aperture 2 5 1 Images will not often be used by observers except for target acquisition in which case the instrument mode can be specified as ACQ and all parameters except the exposure time are set to default values However HSP images may also have some other uses e g an image could be taken after a target acquisition to confirm the success of the acquisition An image may be acquired using any of the IDTs including the polarimeter There is an overhead of about 25 ms per point in the image so that a 20 x 20 target acquisition scan requires at least 10 s This overhead time is not included when specifying the expos
43. lter polarizer combination There is also a clear window with two small apertures which can be used for photometry and a 6 arcsecond diameter finding aperture Linear polarization for a particular bandpass is measured by deriving the Stokes parameters Q and U from observations through each of the four polaroids in succession The internal IDT aperture for the polarimetric IDT is 180 um in diameter the same as for the photometric IDTs however because there is no relay mirror to change the plate scale this corresponds to 0 65 arcseconds on the sky Thus the internal aperture is slightly smaller than the 1 arcsecond focal plane apertures and the effective aperture diameter for the polarimeter is 0 65 arcseconds This affects the accuracy of polarimetry because the degraded HST image puts more energy near the aperture edge and the smaller effective aperture diameter exacerbates the effects of pointing errors and jitter For some observations the polarimeter on the Faint Object Spectrograph might be better than that on the HSP For example the FOS would usually be preferable for a source that has a polarized continuum contaminated by unpolarized line emission On the other hand the FOS polarimeter may not be as well calibrated as the HSP polarimeter during the initial phases of the HST mission See the FOS Instrument Handbook for details on the FOS polarimeter Observers planning to do polarimetry are encouraged to contact the STScI for advice on whic
44. mainly to Chapters 3 and 4 and may often find that the careful construction of complicated observing programs is driven by the constraints described in Chapter 3 Some observing programs will inevitably require more detailed information about the HSP than is given here For example it is possible to write special purpose programs for a micropro cessor inside the HSP that controls observing sequences but this manual does not contain enough information to determine precisely what can and cannot be done with such programs If you require such detailed information it is available either from the Space Telescope Science Institute or from the documents listed in the bibliography of this manual As time passes there will undoubtedly be changes in this manual Chapters 3 and 4 are especially vulnerable to changing as our knowledge of the instrument improves Consequently users should be wary of using outdated versions of the manual Suggestions for improvements are welcome and should be addressed to the authors 1 2 Acronyms Acronyms are a necessary 1f often overused aid in reducing the length of NASA documents The following acronyms may rear their heads in this manual A D BD CVZ D A FGS FOC FOS GSFC GHRS HSP HST IDT NASA NSSC 1 ODS OTA PAD PDB PMT RAM ROM SCUM SOGS STScI STSDAS TAV TBD TDRSS UV WF PC HSP Instrument Handbook Version 2 0 Table 1 1 Acronyms Analog to Digital Bus Director Continuous Viewin
45. ncoming beam transmits part of the incident light to a filter and 1 arcsecond aperture The reflected beam is totally internally reflected by a right angle prism made of suprasil it then passes through another filter a suprasil rod which compensates for the longer path followed by the reflected beam and another 1 arcsecond aperture In all cases the transmitted beam passes through the short wavelength filter and the reflected beam goes through the long wavelength filter of the pair Using this prism beamsplitter mode PRISM on the proposal forms it is possible to measure an target s brightness in two colors merely by moving the IDT beam from one aperture to the other rather than by slewing the HST permitting observations in the two bandpasses separated by only about 10 milliseconds rather than by the thirty seconds required for an HST slew Thus the prisms permit nearly simultaneous observations in two colors HSP Instrument Handbook Version 2 0 Figure 2 4 VIS IDT Apertures and Filters 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 3200 3400 3600 3800 4000 EN RARA DADI RI NUDO DAD HA NA DAD DARI E DURI DODO MAAA NAAA SAAS MAD JE ULI DIO UD Nd DINI ELI LI EDI EEE 4000 4000 3800 13 12 11 10 9 8 7 6 5 4 3 2 1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 43800 E13 ey ee pepe AAA AAA AAA AAA Aaa 13 4 360012 F
46. nd is always at least 14 larger than this because of data added by the spacecraft computer e g error correction bits The bandwidth available to the HSP is reduced even more if other HST instruments are being used at the same time as will often be the case There are various restrictions that arise for the three different link rates When the HSP is producing data more slowly than 4 kbs the data rate generally places no restrictions on the total length of the observation time If the 1 Mbs link is required then the length of the observation will be limited to the tape recorder capacity about 10 minutes of continuous data or to the duration 22 HSP Instrument Handbook Version 2 0 of the 1 Mbs downlink 20 minutes on the average Between 4 kbs and 32 kbs the length of the observation may also be limited if the tape recorder is not available the data will have to be sent to the ground at 1 Mbs To determine whether these restriction are important for a particular observation you need to know the following information 1 Is the target in the continuous viewing zone CVZ Targets in the CVZ are continuously visible for several days during certain phases of HST s 56 day orbital precession Targets not in the CVZ are occulted by the earth on every orbit 2 What is the required data rate R gt 1 14n t where is the sample time determined by your scientific objectives and n is the number of bits per sample determined from t and
47. ne benefit of the programmability of the high voltage is that it provides a means of extending the dynamic range of the detectors in their analog data format The minimum sample time in the analog data format is set by the analog to digital conversion time of 128 ys The true time resolution in analog data format is somewhat larger than this it is determined by the time constant of the current amplifier which ranges from 4 ms in the 1 nA range to 0 4 ms in the 10 uA range It should be emphasized that the effective integration time when collecting data with the analog format is always very short For example even if the sample time is specified to be 1 sec the effective integration time is only 1 ms Thus decreasing the sampling rate leads to widely spaced short samples of the brightness of the star but does not increase the accuracy of measurement for each sample The number of samples required to achieve a specified accuracy using the analog format is essentially independent of the sample time and may be very large for faint targets In the pulse counting digital data format the output of the preamplifiers which provide a voltage gain of about 7 is received by pulse amplifier discriminators PADs The PADs amplify and detect pulses above a threshold set by an 8 bit binary control input enabling the signal to noise ratio to be optimized for any high voltage setting The PAD thresholds are usually set by STScI and will rarely be of concern to
48. on data are all based on pre launch data but the throughput data include the effect of the spherical aberration During the Orbital and Science Verification periods after launch the HSP VIS detector has exhibited some loss of sensitivity STScI can be contacted for more current information as it becomes available Some of the data included in this chapter are 1 Transmission and or reflectivity as a function of wavelength for all optical elements filters mirrors polarizers and beamsplitters 2 Tables giving nominal descriptions of all filters name central wavelength FWHM transmission etc 3 Quantum efficiency as a function of wavelength and dark count rates for detectors 4 Figures giving time to reach S N 100 for a star of a given magnitude and effective temperature 5 Nominal background counting rates through various filters 6 The time required for target acquisition as a function of magnitude and color of the target Several explanatory comments apply to all the tables and figures 1 Filter names are all of the form Fxxxw where xxx is the central wavelength of the filter in nm and w is a measure of the width of the filter bandpass with the following approximate ranges N narrow FWHM lt 5 of central wavelength M medium 5 lt FWHM lt 15 W wide FWHM gt 15 LP longpass filter passes all wavelengths longward of xxx 2 Throughput means the peak efficiency for the entire HSP HST
49. ot be important For each filter plate there is an aperture plate located at the HST focal surface that contains 48 apertures arranged in two columns that are positioned directly behind the corresponding columns of filters Nine of the filters are associated with four apertures each two with diameters of 1 arcsecond 280 um and two with diameters of 0 4 arcseconds 112 ym Due to space limitations one filter is associated with only three apertures and two other filters are associated with two apertures each The thirteenth filter of double width is a clear window and has five associated apertures including one of 10 arcsecond diameter for target acquisition The VIS detector has one additional aperture that also passes light to the PMT see 2 2 3 The choice of 1 0 and 0 4 arcsecond apertures was made on the basis of 6 HSP Instrument Handbook Version 2 0 the specified performance of the HST image at the HSP location 8 arcminutes off axis However the degraded image caused by spherical aberration severely limits the utility of the 0 4 arcsecond apertures because the amount of energy encircled is only 20 of that expected Normally therefore the 1 0 arcsecond apertures will be used for most observations The HST is commanded to point so that the target s position in the HST focal plane coincides with the particular filter aperture combination desired Light from the target is then focused on the dissector cathode by the relay mirror The
50. other filters on POL have polarizers and can be used only for polarimetry 2 2 4 Figure 2 2 shows the X and Y reference axes that are used if it is necessary to specify a particular orientation for an HSP observation using the ORIENT special requirement or a special position for a target in an aperture using the POS TARG special requirement For example the acceptable range of orientations may be restricted to insure that an aperture to be used for mea HSP Instrument Handbook Version 2 0 7 Figure 2 3 HSP Filter Aperture Tube Configuration surement of the sky brightness will not be contaminated by field star See 2 5 2 for discussion of sky subtraction using the HSP Notice that filter changes generally require the HST to slew from one aperture to another this requires about 30 seconds for two apertures on the same IDT and about 60 seconds for two apertures on different IDTs The slew time determines how rapidly multicolor photometry can be done There are two exceptions to this restriction rapid two color observations can be made either in PRISM mode with detectors VIS UV1 and UV2 or in SPLIT mode using PMT and VIS 2 2 2 Two Color Photometry with Prisms On each photometry IDT there is a beamsplitter prism combination that divides the light of an appropriately placed target between two 1 arcsecond apertures that have different filters see Figures 2 4 through 2 6 A partially reflecting MgF plate mounted at 45 to the i
51. r then its position is transmitted to HST Obviously the observer must be present at the STScl if an Interactive acquisition is necessary HSP Instrument Handbook Version 2 0 17 In many cases the target acquisition image can be taken in advance of the actual observation an Early acquisition making real time interaction with HST unnecessary This avoids both the necessity that the observer be present for the observations and difficulties with real time interactions with HST Early acquisitions may also make use of the imaging instruments onboard HST the WF PC and the FOC If the field is very complicated the target faint or the target s ultraviolet magnitude very uncertain then it may prove useful or necessary to get a Wide Field Camera image of the field before the HSP observation The pointing requirements for target acquisition by the WF PC are obviously much less stringent than those of the HSP Unfortunately the long slews required to move a target from the WF PC to the HSP will often preclude the use of the same guide stars for the two instruments this will mean that it will still be necessary to perform some sort of target acquisition with the HSP before observing the target though it may be possible to use a nearby star that is suitable for an Onboard acquisition See the Target Acquisition Handbooks for the HSP and the other instruments for more information on various strategies for difficult cases For faint targets my gt 20 d
52. r 10 photometry The current scheduling procedures appear to be adequate in achieving thermal stability in the detectors The changing temperature of the HSP can lead to systematic variations in the counting rate The photocathode efficiency can vary as a function of temperature this will be important for the PMT and possibly the bialkali IDTs VIS and POL but should not affect the CsTe IDTs UV1 and UV2 which have photocathodes with much larger work functions All voltages produced by electronic power supplies will also vary with temperature Most of these effects will be removed by STScI through calibration observations at different temperatures 3 3 3 Reducing Systematic Errors Many of the systematic errors can be reduced greatly by observing a calibration target before and after observing program targets The STScI will eventually determine how often such cali bration observations must be done to achieve a given level of accuracy Note however that very critical observations probably will always require extra calibrations which will count as part of your observing time and which must be requested as separate exposures in your proposal Chapter 5 describes the standard calibrations that STScI expects to supply for the HSP HSP Instrument Handbook Version 2 0 25 Chapter 4 Instrument Performance 4 1 Sensitivity of the HSP This section consists mainly of figures and tables describing the sensitivity of the HSP The filter transmissi
53. rate out of the HSP when the sample time is short Except in a few ambiguous cases the STScI should be able to determine which data format is best for a particular observation If necessary the data format can by specified on the observing form using the optional DATA FORMAT parameter Note that the ALL format allows the simultaneous measurement of the IDT output using the pulse counting and current methods This is useful for cross calibration of the two techniques and for observing bright stars with count rates near the limit of the pulse counting modes typically between 10 and 2 x 10 cts s Any data format may be used with any observing mode though only the WORD and ANALOG formats are permitted for onboard target acquisitions 3 2 The HSP HST System This section describes aspects of the interaction of the HSP and the HST some of which are obvious and some of which are quite subtle 3 2 1 Changing Filters with the HSP The HSP s filter aperture mechanism requires the HST to execute small slews to move the target from one filter to another This means that the time to change filters is determined by the time for HST to do a small angle maneuver which turns out to be about 30 seconds for all slews shorter than 1 arcminute This may seem surprisingly long it is necessary to move slowly to avoid setting up long lived oscillations in HST s solar panels Consequently when doing multicolor photometry with the HSP it is ineffici
54. reformatted data produced by step 1 above are readily available to the observer A single observation can generate up to 8 separate data files a STAR SKY observation using the ALL data format will generate an uncalibrated data file and a calibrated data file for each of the star digital star analog sky digital and sky analog data The pipeline calibration products will probably be sufficient for most observers However if an observer wishes to recalibrate her data perhaps using a different calibration table the pipeline software is available in STSDAS Refer to the STSDAS Calibration Guide for more information HSP Instrument Handbook Version 2 0 43 Note that the sky background is not subtracted from the star sky measurement It was decided that sky subtraction is sufficiently complicated that it is not reasonable to include it in the automated pipeline Instead it will be the observer s responsibility to decide how the sky measurements are to be averaged and interpolated before they are subtracted from the star measurements Note also that the HSP count rates are not translated either to absolute fluxes or to a standard magnitude system Both of these conversions depend on knowing the spectral energy distribution of the target star Keywords in the header of the data will allow conversion to fluxes the Science Data Analysis System STSDAS at STScI will include the tools that are necessary to convert HSP count rates to a standard magnit
55. resulting photoelectrons are magnetically focused and deflected in the forward section of the image dissector so that the photocurrent is directed through a 180 um aperture corresponding to 1 arcsecond on the sky This aperture connects the forward section of the detector to a 12 stage photomultiplier section Thus with no moving parts 48 different filter aperture combinations are available for each photometry detector in the HSP Not all of these are unique however because of duplicate filters and duplicate apertures associated with each filter The following series of four charts Figures 2 3 through 2 7 show the filter and aperture configuration for the four HSP images dissector tubes On the left side of each filter strip from top to bottom the following information is provided 1 The filter designation in PDB syntax 2 The obsolete original HSP team filter designation provided for reference to old documentation only 3 The filter designation in current proposal syntax For each aperture the following information is provided from top to bottom 1 The aperture designation in PDB syntax 2 The obsolete original HSP team aperture designation provided for refer ence to old documentation only 3 The aperture designation in current proposal syntax There are three so called dark apertures on each IDT that are labeled D1 D2 and D3 These apertures represent the locations on the solid part of the faceplate to wh
56. s made with the HSP 3 1 Internal Details of the HSP 3 1 1 The Bus Director Individual observing sequences in the HSP are carried out by a nanoprocessor called the Bus Director BD The BD executes a very limited set of 16 instructions that do things like load the latches of a particular detector with deflection settings cause the contents of a counter or an A D converter to be placed into the science data buffer loop a specified number of times or wait a specified number of clock cycles One clock cycle is 1 1 024 MHz for convenience this usually is referred to as 1 tick Thus a sequence of 100 1 sec samples on a star is executed by a BD program that loops 100 times through instructions that start a counter wait 1 sec then stop the counter and put its contents in the science data buffer All of the different data formats and modes that are described below are the result of standard BD programs however it is also possible to write non standard programs to produce new modes or formats e g a Star Sky Dark sequence that measures the dark counting rate separately from the sky background rate or a data format in which only the top two bytes of the three byte digital counter are read out It is far beyond the scope of this manual to give enough information for the reader to write his or her own BD programs The HSP team has a designed a language and produced a compiler for special Bus Director programs Contact the HSP team for
57. s and Data Products This chapter describes the way HSP data are usually calibrated and what data products result 5 1 Pipeline Calibrations The raw data received from the HST pass through an automatic calibration procedure called the pipeline before it is received by the observer For the HSP the pipeline performs 6 steps 1 Reformatting The data are put in a standard form that is independent of the par ticular way it was collected Interleaved data taken in STAR SKY mode are divided into two files data taken with the ALL data format is split into separate digital and analog files Each data sample which may be from 8 bits to 24 bits long is converted to a 32 bit floating point number The data is written to a FITS like format called GEIS format which can be read directly by the STSDAS analysis routines 2 Convert counts to count rates and apply deadtime correction For pulse counting digital data the raw counts are divided by the sample time to yield count rates which are then corrected for the non linearities caused by the deadtime of the counting electronics This correction is 1 for counting rates of about 2 5 x 10 counts s The deadtime is known from laboratory measurements to be a weak function of temperature so it should be possible to make accurate deadtime corrections for count rates up to at least 10 counts s 3 Subtract dark counts or currents The standard dark contribution from the phototube is sub
58. section briefly summarizes that document In a Blind target acquisition the target is put directly in the desired 1 0 arcsecond aperture This is equivalent to doing no acquisition at all However it usually will be necessary to determine the target position very accurately before going to a small aperture Neither the target position nor the guide star positions will generally be known accurately enough for a Blind acquisition except when the target has been observed previously For the other target acquisition methods the HST will acquire guide stars in such a way that the program star falls within the large finding aperture of the specified image dissector The finding aperture has a diameter of 10 arcseconds for the photometry IDTs and 6 arcseconds for the polarimetry IDT Target positions must be accurate enough that the target will never fall outside the finding aperture A 20 x 20 raster scan covering the finding aperture is then performed by the dissector to form a pseudo image the Acquisition image Acquisitions are requested on the proposal forms with the ACQ mode and must be listed as separate exposures on the exposure logsheet The type of acquisition must be specified using the ONBOARD or INTERACTIVE or EARLY ACQ FOR lines special requirement Typical times required to collect the target acquisition image are given in Table 4 7 Note The degraded images produced by the HST affect the accuracy of the HSP onboard centroid calculation
59. sed 40 HSP Instrument Handbook Version 2 0 Configuration Mode Exposure Time HSP D SINGLE texp Nsamp tsamp taelay where Nsamp is the number of samples desired tsamp is the time for each sample and tgeiay iS the delay time between samples tgeiay is usually zero for these modes HSP PMT VIS SPLIT terp Nsamp tsamp tdetay HSP D1 D3 STAR SKY terp Nsampltsamp tdetay HSP D PRISM STAR SKY terp Nsampltsamp tot taetay tot where tsamp tot is the sum of the sample times for the two apertures and 4e ay tot is the sum of the delay times for the two apertures tgeiay iS usually 10 milliseconds for each aperture in these modes SO tgetay tot 18 usually 20 milliseconds If a sequence containing a number of exposures is defined then the total exposure time for the sequence is simply the sum of the individual exposure times The sample time and number of samples needed for a particular observation are determined by the scientific objectives of the program the brightness of the target the filter used the time resolution needed the signal to noise required etc The next section shows how to calculate the sample time and number of samples for a typical HSP observation 4 2 2 Photometry of the Crab Pulsar The Crab pulsar is a classic object for high speed photometry The scientific goal of this sample program is to measure the width of the ultraviolet pulse from the Crab pulsar The time averaged de redd
60. sed for polarimetry and a beamsplitter allows the photomultiplier PMT along with the bialkali photometry dissector VIS to be used for simultaneous observations in two Note that the polarimeter also has one clear filter that can be used for photometry 4 HSP Instrument Handbook Version 2 0 Figure 2 1 HSP Optics and Detectors colors e g for occultations For convenience we will refer to the photometric polarimetric and PMT configurations but in most respects the operation of the various detectors is identical For the purposes of the HST proposal forms the HSP has the following configurations and modes Table 2 1 HSP Configurations and Modes Configuration Modes HSP UV1 UV2 VIS SINGLE STAR SKY ACQ IMAGE PRISM HSP POL SINGLE STAR SKY ACQ IMAGE HSP PMT SINGLE HSP D Ds STAR SKY HSP PMT VIS SPLIT All these modes are discussed in the following paragraphs The ACQ mode is used for target acquisition and is also discussed in 82 5 1 and in the HSP Target Acquisition Handbook See the Hubble Space Telescope Phase II Proposal Instructions for information about how to specify the various configurations and modes on the proposal forms 2 2 1 Single Color Photometry Consider first photometric observations which can be carried out using the mode SINGLE This mode can be used with any of the five HSP detectors Light from the HST enters the HSP through HSP Instrument Handbook Version 2 0 5 Figure
61. servations 6 0 10 0 arcsecond for target acquisition Filters 23 UV and visual filters from 1200 A to 7500 A Polarimetry 4 UV filters 2 polarimetric accuracy Operation Telescope must slew to move star from one filter to another Slew time 30 60 s limits rate at which multicolor pho tometry is possible There are four filter pairs with beam splitters that can be used for two color photometry without moving telescope for these filter pairs can get simultaneous or nearly simultaneous separated by only 10 milliseconds two color photometry 2 2 Detectors and Optics Configurations The HSP has quite an unusual design in that it has no moving parts Figure 2 1 shows a sketch of the arrangement of the detectors and optics in the HSP There are five detectors in the instrument four image dissector tubes IDTs and one photomultiplier tube The former are ITT 4012RP Vidissectors two with CsTe photocathodes on MgF faceplates sensitive from 1200 A to 3000 A and two with bialkali cathodes on suprasil faceplates sensitive from 1600 A to about 7000 A Each image dissector tube its voltage divider network and its deflection and focus coils are all contained in a double magnetic shield within the housing The photomultiplier is a Hamamatsu R6665 with a GaAs photocathode Three of the image dissectors the two CsTe tubes called UVI and UV2 and one of the bialkali tubes VIS are used for photometry The second bialkali dissector POL is u
62. system including reflectivity of mirrors filter polarizer and beamsplitter transmis sion and detector efficiency These values were calculated using the portable HSP simulator software and include the spherical aberration Comparison with observations show that these numbers are accurate 10 for most apertures The hspsim program appears to be underestimating the through put for the shortest wavelength filters and those below about 150 nm ex cluding the POL filters can be estimated to be about a factor of two or three above the tabular values 3 Transmission means the peak value for the given optical element filter polarizer etc alone not including any other elements in system At the end of the chapter is an example that demonstrates how to use the information in the tables and figures to estimate exposure times for HSP observations 26 HSP Instrument Handbook Version 2 0 Table 4 1 HSP Photometry Filters Name A FWHM Transmission Throughput Remarks A A 4 4 F122M 1220 130 7 0 005 F135W 1350 230 12 0 015 F145M 1450 200 13 0 032 F152M 1520 180 13 0 043 F179M 1790 220 30 0 31 F184W 1840 370 31 0 37 F218M 2180 170 35 0 48 F220W 2200 350 35 0 49 F240W 2400 550 48 0 64 F248M 2480 370 35 0 46 F262M 2620 290 33 0 1 UV2 IDT 0 5 VIS IDT F278N 2780 140 33 0 18 F284M 2840 380 31 0 33 F320N 3200 160 26 0 32 PMT beamsplitter VIS F355M 3550 310 19 0 29 u F419N 4190 190 31 0 66 v F450
63. t Much useful criticism of the HSP Instrument Handbook was provided by Bob Bless Joe Dolan Howard Bond and Lisa Walter however any remaining problems are the responsibility of the authors HSP Instrument Handbook Version 2 0 3 Chapter 2 Overview of the HSP The High Speed Photometer HSP exploits the capabilities of the HST by making photometric measurements over visual and ultraviolet UV wavelengths at rates up to 10 Hz and by measuring very low amplitude variability especially for hotter stars in the UV A secondary purpose of the instrument is to measure linear polarization in the near UV The HSP has several advantages over similar ground based instruments 1 UV wavelength coverage 2 Smaller apertures permitting higher spatial resolution and reducing the sky back ground 3 No atmospheric absorption or scintillation leading to higher photometric accuracy and the ability to use very short sample times In what follows we will present an overview of the HSP its optics and detectors its electronics its mechanical structure and finally some observational considerations 2 1 Summary of HSP Characteristics Quantum Efficiency 0 1 3 throughput for entire HSP HST system Time Resolution 10 7 us pulse counting mode count rate lt 10 cts s l ms current mode count rate gt 10 cts s Photometric Accuracy Systematic errors lt 2 from V 0 to V 20 Apertures 1 0 arcsecond diameter for normal ob
64. tracted Nominal dark counts and currents are known as a function of both the position on the IDT cathode and the detector temperature Notice that if a special dark calibration is requested by the observer via the DARK internal calibration target request described in the Phase II Proposal Instructions it will not be subtracted in the pipeline instead it will have to be subtracted using the general purpose data analysis system STSDAS see below 4 Convert currents to equivalent count rates For current analog data the photocur rents that were measured are converted to the effective count rates that would have been measured by a pulse counting system with zero deadtime 5 Correct for the instrumental efficiency The instrumental efficiency is measured by observing a standard star through the same aperture filter combination Comparison of observations of the same standard star taken at different times allows the removal of changes in the HSP sensitivity as a function of time The pipeline calibration program computes the HSP count rate the target would have had if the HSP sensitivity had not changed 6 Divide observations of extended objects by aperture area Note that this applies to sky observations as well as to observations of extended targets 5 2 Data Products The results of the pipeline calibration are files containing the HSP count rates as a function of time for the star sky and if it was measured the sky In addition the
65. try have been loaded in advance and are used in an off the shelf fashion It is possible however to load a special Bus Director program of your own Three Color Photometry or rapid readout area scans are examples of what can be considered The Bus Director Compiler BDC is a program that reads in a pro gram specification in the form of simple words start counter stop counter etc and produces the opcodes that implement this program In addition we have simulated the operation of the Bus Director in a second program which can read in any bus director program and execute it with a printout giving actual timestamps when counters are started and stopped and so on Finally a few words should be said about the various HSP simulator programs The original hspsim was written at the STScI and is still available there The HSP team also has a simulator program that uses the same data files but has a little different look and feel The HSP team version is written is portable C contains no site dependent graphics code and has been compiled ond run on several different computers and operating systems It has a simple tabular output and can be run either interactively or in batch mode Another feature is that the user can specify wildcards that can select all the filters on a detector a given filter on any detector that has it or even all filters on all detectors The input spectrum can be a blackbody a power law or user defined A library of K
66. ude system if the target star s color is known or if some shape for the spectrum is assumed STSDAS will also have access to the calibration data that are required for these translations e g color terms for standard filters and the absolute flux distribution for calibration stars Consult the STSDAS Users Guide for more information An advantage of supplying the data in the form of HSP count rates rather than absolute fluxes is that the former are independent of the flux distribution assumed for the standard stars Thus if the flux scale of the standard spectra is revised the HSP count rates will not change 5 3 Special Calibrations Calibration observations made as a service by the STScI will be sufficient to calibrate most HSP observations However there will inevitably be some observations that require special calibrations For example a special calibration may be required to measure the strongly varying sky background that is seen during a lunar occultation As another example it may be desirable to observe a standard star before and after the target is observed in order to remove small systematic effects see Chapter 3 for more discussion of this Any special calibration observations must be requested as part of the observing proposal The observer is responsible for applying the calibration to the data Attempts to derive standard calibrations have been thwarted by the repeatability problems in the FGS and the unexplained instabilities
67. ure time for the image but is charged to the observer 2 3 Electronics Figure 2 8 shows a block diagram of the HSP electronics All five detectors have identical electronic subsystems with the exception of the photomultiplier which does not have the ampli fiers needed in the image dissectors to drive focus and deflection coils The horizontal and vertical deflections and focus settings are 12 bit programmable quantities A change of 1 in the deflection corresponds to a beam motion of about 4 um 0 014 arcseconds for the POL detector 0 02 arc seconds for the others The 8 bit programmable high voltage power supplies provide negative DC voltages between 1400 and 2600 volts for the detectors The settings of all internal HSP quantities will usually be handled automatically by STScI although there may be rare observations that require changing the high voltage discriminator settings etc to get the best performance from the HSP The output of the detectors can be measured by counting pulses by measuring the photocur rent or by doing both simultaneously In the current analog data format a current to voltage converter measures detector current outputs over a range of 1 nA to 10 pA full scale in five decade gain settings selectable by discrete command inputs The amplifier output is converted to a 12 bit digital value by an A D converter The analog data format will be used for stars that are too bright for the pulse counting data formats O
68. urucz model spectra is also available for a more realistic input Documentation and programs for these resources are available from the HSP team Write to jwp sal wisc edu for details HSP Instrument Handbook Version 2 0 Table of Contents Chapter 1 Introduction 1 1 How to Use This Manual 1 2 Acronyms 1 3 Acknowledgements Chapter 2 Overview of the HSP 2 1 Summary of HSP Characteristics 2 2 Detectors and Optics Configurations 2 2 1 Single Color Photometry Loe 2 2 2 Two Color Photometry with Prisms 2 2 3 Two Color Photometry with the PMT 2 2 4 Polarimetry 2 2 5 Images with the HSP 2 3 Electronics 2 4 Mechanical Structure and Thermal Characteristics 2 5 Observing with the HSP 2 5 1 Target Acquisition 2 5 2 Sky Subtraction Modes 2 5 3 Occultation Observations with the HSP 2 5 4 Other Useful Information Chapter 3 Details of the HSP HST System 3 1 Internal Details of the HSP 3 1 1 The Bus Director 3 1 2 Standard Data Formats 3 2 The HSP HST System 3 2 1 Changing Filters with the HSP 3 2 2 Limits to the Length of Uninterrupted Observations 3 2 3 Unequally Spaced Data 3 2 4 Absolute Timing of Observations 3 3 Sources of Noise and Systematic Errors 3 3 1 Noise 3 3 2 Systematic Errors 3 3 3 Reducing Systematic Errors Chapter 4 Instrument Performance 4 1 Sensitivity of the HSP 4 2 Planning a Typical Observation with the HSP 4 2 1 How to Calculate Exposure Times 4 2 2 Photometry of the Crab Pulsar Chapter 5 St

HIGH SPEED PHOTOMETER INSTRUMENT HANDBOOK

Contents

Download Pdf Manuals

Related Search

Related Contents