6075( 9) - 11/22/95 14:38 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6075 Version: 9 Check-in Date: ********** 1.Proposal Title: Determination of Fundamental System Parameters for Cataclysmic Variables ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Hot Stars GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Ronald Gilliland Space Telescope Science Institute CoI: Knox Long Space Telescope Science Institute N ------------------------------------------------------------------------------------ 6. Abstract Cataclysmic variables (CVs) have been extensively studied over the past two decades with X-ray, UV, optical and IR observations. The rapid variations present in these interacting binary systems allow direct study of astrophysical processes occurring on dynamic, thermal and thermonuclear timescales. Interpretation of results for these intensive studies of CVs relies in part on poorly determined fundamental parameters for most systems, the weakest link of which are masses as constrained by radial velocity amplitudes for the white dwarf primaries. We propose a new determination of orbital velocity amplitudes (K_1) using observations in the far UV where in a few systems the white dwarf spectrum is clearly visible. These observations will exploit the unique capabilities of HST and GHRS for a system of particular interest: U Gem. These observations will provide a definitive measure of K_1 for this pivotal dwarf nova, and allow for crucial checks of internal consistency on the solutions. Rapid oscillations will be analyzed to enable a complementary orbital delay timing solution. The resulting unique data sets are expected to support numerous other investigations of these white dwarfs which periodically accrete mass during outbursts. ------------------------------------------------------------------------------------ 6075( 9) - 11/22/95 14:38 - [ 2] Observations Description ------------------------ U Gem will be observed in such a way as to retain reliable information on radial velocities, and at the same time provide high time resolution which could have important secondary benefits (through the oscillations and tracing eclipses). Most of the specified coverage period will be devoted to taking rapidly repeated ACCUM mode spectra with G140L covering the wavelength range 1160-1445A. STEP-PATT = 3 will provide full COMB addition and 1/4 diode substepping, the per repeat overhead is 5.9s. Integration times are quantized in multiples of 3.2s and an integration time of 9.6s will be adopted to provide a duty cycle of 62% on a cycle cadence of 15.5s. The current HST control system supports up to 999 repeats without encountering memory limits or data rate problems. Thus individual exposure logsheet lines will specify ~184 repeats and take ~2800s (+4 minute startup overhead) to fill each HST orbit visibility period. At each orbit break a WAVECAL should be obtained WITHOUT MOVING the carousel; the WAVECAL will be cycled continuously throughout the occultation to provide direct calibration of geomagnetic image motion and thermal drifts. The HST-FOS spectra for U Gem (T~32,000K); shows a dearth of lines between 1405 and 1550 A, this plus a rising UV flux argue for the far UV wavelength setting. We simulated the precisions that may be expected for U Gem by generating a large number of spectra (independent noise) with lines as in U Gem and S/N as appropriate to the star The following table summarizes the Poisson statistics limited results of the proposed observations. Star wave cts/s S/N dV dK Nobs U Gem 1300 1.1 12.3 4.2 1.0 48 Assumes G140L with the SSA. (Counts with LSA would be 80% higher; the improved spectral resolution almost exactly offsets the count rate for radial velocity determinations.) Signal to noise is quoted per 1/2 diode substep after summing the individual spectra over 8 minute windows. dV is expected per 8 minute spectrum velocity precision (dK). Precision on K_1 given N_obs analyzed exposures of 8 minutes (selection of 8 minutes is arbitrary). In estimating final precisions instrument drifts and external errors must also be considered. The selection of G140L with a resolution of ~130 km/s implies that U Gem will generate orbital motions at +/-1 diode, We desire accuracy of 4 km/s = 0.03 diode. There are a number of contributing errors to consider: (1) HST orbital motion at +/-7.5 km/s (GHRS Doppler compensation is not of use at G140L given quantization at 1/8th diode steps) -- this is known exactly and can be removed perfectly. (2) Geomagnetic field induced motion in GHRS at ~0.1 diode level ~13 km/s; phase is predictable and with calibration of scale using repeated WAVECALS during occultation the residual should be <2 km/s. (3) Thermal drifts ~0.1 diode per orbit; telemetry reports relevant temperatures and these observations will be internally well calibrated -- residual <2 km/s. (4) Spacecraft guiding ~0.007" (typical) ~0.016 diodes ~2 km/s (quoted diode and km/s amplitudes have been reduced by a factor of two -- the SSA does not ``see" full amplitude of offset errors -- Gilliland et al 1992). All external sources of error will be controlled to <4 km/s per 8 minute spectrum with no significant uncompensated drift on longer timescales. (See Brown, Gilliland et al 1991 for an example of Doppler velocity measures to precisions of ~0.001 CCD pixels given high S/N and internal calibrations.) Note: All else being equal the precisions scale (with obvious signs) linearly with S/N per resolution element, and as the square root of dispersion and number of available spectral lines. Going to the GHRS intermediate (R~20,000) resolution grating would give Poisson limiting precisions poorer by a factor of about 3, but at the higher dispersion external drifts would be ignorable. U Gem could be done to about the same confidence level (but not better) with G160M observations (but check versus independent lines would not be available, and most serendipitous science would be sacrificed). Nine HST orbits are required to obtain full phase sampling (phase of 4 h 15 min U Gem orbit changes by 0.38 each HST orbit and the observing window spans 0.18) on U Gem, with ~60% redundancy -- invaluable for checking solution stability. Real Time Justification ----------------------- The U Gem observations should be scheduled at 70 +/- 15 days past an outburst. This will provide the best combination of flux and line depth in support of the radial velocity determinations. This will require special coordination, but is not a constraint that requires target of opportunity status. U Gem has an outburst about every 118 days, therefore there will be three chances to schedule within the cycle. Calibration Justification ------------------------- The GHRS Side 1 photocathode has substantial granularity. There is no general ``flat-field" available to correct GHRS spectra, rather FP-SPLITs are recommended where the S/N is anticipated to be large enough for the granularity to matter. For these observations the flux is too low to effectively do FP- SPLITs, and such would not be a good idea anyway in a program aimed primarily at accurate radial velocities. Support of this program will require adding a general calibration to actually derive a flat-field for G140L -- this is the only grating where this is feasible (in terms of cost), and it is also the grating for which flat-fielding is most needed. This calibration would probably be done for the general GO program anyway, and should require only two orbits to perform. We must carefully calibrate the GIMP effect via WAVECALs during occultations; this program will provide a general calibration test of GIMP for Side 1. The commented out exposure logsheet lines (in the as submitted version): 15,25,35,45,55,65,75,85 must be restored and scheduled as occultation interleavers. The Number_of_Iterations on line 95 should be increased to 220 to fill out the final occultation. IT IS ESSENTIAL TO THE SUCCESS OF THIS PROGRAM THAT NO CARROUSEL MOVEMENTS OCCUR AFTER THE START OF LINE 10 THROUGH COMPLETION OF LINE 95. WE NEED SPYBAL=NO TO BE INVOKED SPYBALS (at the science wavelength setting) are allowed for at the ends of orbits 1, 2 and 4 (via SCI- SPYBAL on lines 16, 26, 46). Additional Comments ------------------- We will propose for ground-based time to obtain recent epoch, complementary optical spectroscopy. Comparison of the UV- based results with the optical spectra will facilitate a test of the optical emission line approach to K_1 determination (for which 100's of papers exist in the literature). While it would be good for such supporting observations to be simultaneous with the HST observations, this will not be a requirement on the scheduling. ------------------------------------------------------------------------------------ 6075( 9) - 11/22/95 14:38 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: stsci Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6075( 9) - 11/22/95 14:38 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 U-GEM Star, Dwarf Nova, RA=07H 55M 5.29S +/- 0.01S, 2000 V=14.5 +/- 0.1 Interacting Binary DEC=22D 00' 05.7" +/- 0.1", B-V = 0.0 +/- 0.1 PLATE-ID=02UF 6075( 9) - 11/22/95 14:38 - [ 5] Visit: 01 Visit Requirements: BETWEEN 10-NOV-95 AND 20-DEC-95 On Hold Comments: Schedule 60 +/- 10 days after PI notice Additional Comments: If necessary the GHRS Optional Parameter SAA-CONTOUR=HIGH-NOISE may be set to allow scheduling 9 orbits SAA free. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 U-GEM HRS ACQ 2.0 MIRROR-N1 1 18S ONBOARD ACQ FOR 2 Comments: Expect 120 to 240 cts per second ------------------------------------------------------------------------------------------------------------------------------------ 2 U-GEM HRS ACQ/PEA 0.25 MIRROR-N1 1 100S ONBOARD ACQ FOR 10-95 KUP ------------------------------------------------------------------------------------------------------------------------------------ 10 U-GEM HRS ACCUM 0.25 G140L 1303 STEP-PATT=3, 40 9.6S SEQ 10 NON-INT; END ORBIT DOPPLER=OFF Comments: This is the only exposure where a normal SPYBAL should occur. ------------------------------------------------------------------------------------------------------------------------------------ 15 WAVE HRS ACCUM SC2 G140L 1303 STEP-PATT=3, 88 9.6S SEQ 15 NON-INT DOPPLER=OFF, SPYBAL=NO Comments: Odd no. lines interleave to occultation. ------------------------------------------------------------------------------------------------------------------------------------ 16 WAVE HRS ACCUM SC2 G140L 1303 STEP-PATT=3, 1 9.6S DOPPLER=OFF, SCI-SPYBAL=YES Comments: Lines 16, 26, and 46 allow SPYBALs. ------------------------------------------------------------------------------------------------------------------------------------ 20 U-GEM HRS ACCUM 0.25 G140L 1303 STEP-PATT=3, 184 9.6S SEQ 20 NON-INT; END ORBIT DOPPLER=OFF, SPYBAL=NO Comments: Really do want SPYBAL=NO, RPS2 overrides ------------------------------------------------------------------------------------------------------------------------------------ 25 WAVE HRS ACCUM SC2 G140L 1303 STEP-PATT=3, 150 9.6S SEQ 25 NON-INT DOPPLER=OFF, SPYBAL=NO Comments: Odd no. lines interleave to occultation. ------------------------------------------------------------------------------------------------------------------------------------ 26 WAVE HRS ACCUM SC2 G140L 1303 STEP-PATT=3, 1 9.6S DOPPLER=OFF, SCI-SPYBAL=YES Comments: Lines 16, 26, and 46 allow SPYBALs. ------------------------------------------------------------------------------------------------------------------------------------ 30 U-GEM HRS ACCUM 0.25 G140L 1303 STEP-PATT=3, 184 9.6S SEQ 30 NON-INT; END ORBIT DOPPLER=OFF, SPYBAL=NO Comments: Carrousel should not be moved at all 10-95. ------------------------------------------------------------------------------------------------------------------------------------ 35 WAVE HRS ACCUM SC2 G140L 1303 STEP-PATT=3, 150 9.6S SEQ 35 NON-INT DOPPLER=OFF, SPYBAL=NO Comments: Odd no. lines interleave to occultation. ------------------------------------------------------------------------------------------------------------------------------------ 6075( 9) - 11/22/95 14:38 - [ 6] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 40 U-GEM HRS ACCUM 0.25 G140L 1303 STEP-PATT=3, 184 9.6S SEQ 40 NON-INT; END ORBIT DOPPLER=OFF, SPYBAL=NO Comments: Expect count rate of 1 per second per diode. ------------------------------------------------------------------------------------------------------------------------------------ 45 WAVE HRS ACCUM SC2 G140L 1303 STEP-PATT=3, 150 9.6S SEQ 45 NON-INT DOPPLER=OFF, SPYBAL=NO Comments: Odd no. lines interleave to occultation. ------------------------------------------------------------------------------------------------------------------------------------ 46 WAVE HRS ACCUM SC2 G140L 1303 STEP-PATT=3, 1 9.6S DOPPLER=OFF, SCI-SPYBAL=YES Comments: lines 16, 26, and 46 allow SPYBALs. ------------------------------------------------------------------------------------------------------------------------------------ 50 U-GEM HRS ACCUM 0.25 G140L 1303 STEP-PATT=3, 184 9.6S SEQ 50 NON-INT; END ORBIT DOPPLER=OFF, SPYBAL=NO Comments: Num It should be increased on lines 20, 30,40,50,60,70,80. ------------------------------------------------------------------------------------------------------------------------------------ 55 WAVE HRS ACCUM SC2 G140L 1303 STEP-PATT=3, 150 9.6S SEQ 55 NON-INT DOPPLER=OFF, SPYBAL=NO Comments: Odd no. lines interleave to occultation. ------------------------------------------------------------------------------------------------------------------------------------ 60 U-GEM HRS ACCUM 0.25 G140L 1303 STEP-PATT=3, 184 9.6S SEQ 60 NON-INT; END ORBIT DOPPLER=OFF, SPYBAL=NO ------------------------------------------------------------------------------------------------------------------------------------ 65 WAVE HRS ACCUM SC2 G140L 1303 STEP-PATT=3, 150 9.6S SEQ 65 NON-INT DOPPLER=OFF, SPYBAL=NO Comments: Odd no. lines interleave to occultation. ------------------------------------------------------------------------------------------------------------------------------------ 70 U-GEM HRS ACCUM 0.25 G140L 1303 STEP-PATT=3, 184 9.6S SEQ 70 NON-INT; END ORBIT DOPPLER=OFF, SPYBAL=NO ------------------------------------------------------------------------------------------------------------------------------------ 75 WAVE HRS ACCUM SC2 G140L 1303 STEP-PATT=3, 150 9.6S SEQ 75 NON-INT DOPPLER=OFF, SPYBAL=NO Comments: Odd no. lines interleave to occultation. ------------------------------------------------------------------------------------------------------------------------------------ 80 U-GEM HRS ACCUM 0.25 G140L 1303 STEP-PATT=3, 184 9.6S SEQ 80 NON-INT; END ORBIT DOPPLER=OFF, SPYBAL=NO ------------------------------------------------------------------------------------------------------------------------------------ 85 WAVE HRS ACCUM SC2 G140L 1303 STEP-PATT=3, 150 9.6S SEQ 85 NON-INT DOPPLER=OFF, SPYBAL=NO Comments: Odd no. lines interleave to occultation. ------------------------------------------------------------------------------------------------------------------------------------ 6075( 9) - 11/22/95 14:38 - [ 7] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 90 U-GEM HRS ACCUM 0.25 G140L 1303 STEP-PATT=3, 102 9.6S SEQ 90 NON-INT DOPPLER=OFF, SPYBAL=NO ------------------------------------------------------------------------------------------------------------------------------------ 95 WAVE HRS ACCUM SC2 G140L 1303 STEP-PATT=3, 120 9.6S SEQ 95 NON-INT; SAME POS AS 90 DOPPLER=OFF, SPYBAL=NO Comments: Change Num_It from 60 to 220; no slew ------------------------------------------------------------------------------------------------------------------------------------ 6075( 9) - 11/22/95 14:38 - [ 8] Summary Form for Proposal 6075 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAKUP ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters STEP-PATT=3 DOPPLER=OFF SPYBAL=NO SCI-SPYBAL=YES ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Hot Stars ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 10-NOV-95 AND 20-DEC-95 ONBOARD ACQ FOR 2 ONBOARD ACQ FOR 10-95 SEQ 10 NON-INT; END ORBIT SEQ 15 NON-INT SEQ 20 NON-INT; END ORBIT SEQ 25 NON-INT SEQ 30 NON-INT; END ORBIT SEQ 35 NON-INT SEQ 40 NON-INT; END ORBIT SEQ 45 NON-INT SEQ 50 NON-INT; END ORBIT SEQ 55 NON-INT SEQ 60 NON-INT; END ORBIT SEQ 65 NON-INT SEQ 70 NON-INT; END ORBIT SEQ 75 NON-INT SEQ 80 NON-INT; END ORBIT SEQ 85 NON-INT SEQ 90 NON-INT SEQ 95 NON-INT; SAME POS AS 90 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N1 G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names U-GEM WAVE ------------------------------------------------------------------------------------------------------------------------------------