6782( 4) - 02/05/96 22:11 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6782 Version: 4 Check-in Date: 05-Feb-1996 22:05:36 1.Proposal Title: TESTING THE THEORY OF RADIATIVE LEVITATION IN DA WHITE DWARFS ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle HOT STARS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Dr. Jay Holberg University of Arizona CoI: Dr. Martin Barstow University of Leicester N CoI: Dr. Ivan Hubeny Goddard Space Flight Center N CoI: Dr. Thierry Lanz Goddard Space Flight Center N ------------------------------------------------------------------------------------ 6. Abstract We propose GHRS observations of two H-rich DA white dwarfs with temperatures near 40,000K. This temperature defines the critical point, above which the mechanism of radiative levitation becomes efficient enough to prevent elements heavier than H or He from sinking out of the atmospheres of DA white dwarfs under the influence of gravity. Below this temperature, DA atmospheres are observed to be more or less pure hydrogen. However, measurement of photospheric abundances of stars having the same temperatures (and gravities) give quite disparate results - GD394 has a larger heavy element content than predicted, whereas the nearly identical star GD153 has an unexpectedly pure H atmosphere. Unfortunately, near 40,000K, only these two stars are bright enough to be observed at high dispersion with IUE at sufficient S/N. New observations are needed to begin providing the observational evidence necessary to establish the physical mechanisms that determine white dwarf composition, and cause departures from the predictions of radiative levitation theory. ------------------------------------------------------------------------------------ 6782( 4) - 02/05/96 22:11 - [ 2] Observations Description ------------------------ The proposed GHRS observation for each of the two white dwarfs is given below. The spectral coverage and exposure time are given for each spectral setup. All spectra will be obtained using the standard FP-SPLIT=4 option. This is to minimise the effects of fixed pattern detector noise and to easily identify any diode dropouts, which could produce artificial absorption features. Exposure times are set to yield an S/N ~ 20 for each wavelength range. This S/N denotes counts per data point, where each diode is quarter-stepped (each diode is used 4 times in a comb addition to produce the spectrum). This represents STEP- PATTERN=5 for the G160M grating. =5pt 0.2cm begintabbing REJ1614-085 \\\\=PG1057+719, o \\\\=1250-1285 Angstrom \\\\= Si II exposure \\\\=6 min \\\\=10 min, o \\\\=1280-1315 Angstrom \\\\= Si III exposure \\\\=5 min \\\\=9 min, o \\\\=1385-1420 Angstrom \\\\= Si IV exposure \\\\=8 min \\\\=15 min, o \\\\=1520-1555 Angstrom \\\\= C IV exposure \\\\=15 min \\\\=30 min, endtabbing PG 1057+719 lies in the continuous viewing zone (CVZ) and so can be complete in 2 shifts. The brighter RE J1614-085 also requires 2 shifts. Exposure times and signal-to-noise predictions were calculated using SYNPHOT procedures. Synthetic model atmosphere spectra craeted with TLUSTY were used to generate predicted count and count rate spectra using the STSDAS SYNPHOT procedures COUNTRATE and PLSPEC. Real Time Justification ----------------------- None None Calibration Justification ------------------------- Real_Time_Justification Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6782( 4) - 02/05/96 22:11 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 WD1057+719 STAR,DA RA=11H 00M 34.32S +/- J2000 V = 14.7+/-0.1 0.2S,DEC=71D 38' 03.29" +/- B-V = -0.25+/-0.05 0.25",PLATE-ID=01L3 F-CONT(1400)=4.6+/-0.3e-13 Comments: THIS IS A CVZ TARGET Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) B1984.026 0.0 0.0 0.0 2 REJ1614-085 STAR,DA RA=16H 14M 19.14S +/- 0.2S,DEC=- J2000 V = 14.01+/-0.03 8D 33' 26.69" +/- 0.25",PLATE- B-V = -0.25+/-0.03 ID=00TR F-CONT(1400)=8.7+/-0.2e-13 Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) B1983.453 0.0 0.0 0.0 6782( 4) - 02/05/96 22:11 - [ 4] Visit: 01 Visit Requirements: CVZ On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 WD1057+719 HRS ACQ 2.0 MIRROR-N2 1 3.6S ONBOARD ACQ FOR 2 Comments: expected counrate = 6600 c/s ------------------------------------------------------------------------------------------------------------------------------------ 2 WD1057+719 HRS ACQ/PEA 0.25 MIRROR-N2 1 10.0S ONBOARD ACQ FOR 11-41 KUP ------------------------------------------------------------------------------------------------------------------------------------ 11 WD1057+719 HRS ACCUM 0.25 G160M 1251.9 COMB=FOUR,STEP- 1 1632.0S PATT=5,FP- SPLIT=STD Comments: 1260A (Si II Region) ------------------------------------------------------------------------------------------------------------------------------------ 20 WAVE HRS ACCUM SC2 G160M 1296.5 SPYBAL=YES 1 54.4S Comments: WAVECAL for 1300A Region ------------------------------------------------------------------------------------------------------------------------------------ 21 WD1057+719 HRS ACCUM 0.25 G160M 1296.5 COMB=FOUR,STEP- 1 1523.2S PATT=5,FP- SPLIT=STD Comments: 1300A (Si III Region) ------------------------------------------------------------------------------------------------------------------------------------ 30 WAVE HRS ACCUM SC2 G160M 1405.5 SPYBAL=YES 1 54.4S Comments: WAVECAL for 1400 A Region ------------------------------------------------------------------------------------------------------------------------------------ 31 WD1057+719 HRS ACCUM 0.25 G160M 1405.5 COMB=FOUR,STEP- 1 2176.0S PATT=5,FP- SPLIT=STD Comments: 1400A (Si IV Region) ------------------------------------------------------------------------------------------------------------------------------------ 41 WD1057+719 HRS ACCUM 0.25 G160M 1538.7 COMB=FOUR,STEP- 1 3155.2S PATT=5,FP- SPLIT=STD Comments: 1550A (C IV Region) ------------------------------------------------------------------------------------------------------------------------------------ 6782( 4) - 02/05/96 22:11 - [ 5] Visit: 02 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 REJ1614-085 HRS ACQ 2.0 MIRROR-N2 1 3.6S ONBOARD ACQ FOR 2 Comments: expected counrate = 12400 c/s ------------------------------------------------------------------------------------------------------------------------------------ 2 REJ1614-085 HRS ACQ/PEA 0.25 MIRROR-N2 1 10.0S ONBOARD ACQ FOR 11-41 KUP ------------------------------------------------------------------------------------------------------------------------------------ 11 REJ1614-085 HRS ACCUM 0.25 G160M 1251.9 COMB=FOUR,STEP- 1 435.2S PATT=5,FP- SPLIT=STD Comments: 1260A (Si II Region) ------------------------------------------------------------------------------------------------------------------------------------ 20 WAVE HRS ACCUM SC2 G160M 1296.5 SPYBAL=YES 1 54.4S Comments: WAVECAL for 1300A Region ------------------------------------------------------------------------------------------------------------------------------------ 21 REJ1614-085 HRS ACCUM 0.25 G160M 1296.5 COMB=FOUR,STEP- 1 435.2S PATT=5,FP- SPLIT=STD Comments: 1300A (Si III Region) ------------------------------------------------------------------------------------------------------------------------------------ 30 WAVE HRS ACCUM SC2 G160M 1405.5 SPYBAL=YES 1 54.4S Comments: WAVECAL for 1400 A Region ------------------------------------------------------------------------------------------------------------------------------------ 31 REJ1614-085 HRS ACCUM 0.25 G160M 1405.5 COMB=FOUR,STEP- 1 761.6S PATT=5,FP- SPLIT=STD Comments: 1400A (Si IV Region) ------------------------------------------------------------------------------------------------------------------------------------ 41 REJ1614-085 HRS ACCUM 0.25 G160M 1538.7 COMB=FOUR,STEP- 1 1305.6S PATT=5,FP- SPLIT=STD Comments: 1550A (C IV Region) ------------------------------------------------------------------------------------------------------------------------------------ 6782( 4) - 02/05/96 22:11 - [ 6] Summary Form for Proposal 6782 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAKUP ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters COMB=FOUR STEP-PATT=5 FP-SPLIT=STD SPYBAL=YES ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category HOT STARS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CVZ ONBOARD ACQ FOR 2 ONBOARD ACQ FOR 11-41 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N2 G160M ------------------------------------------------------------------------------------------------------------------------------------ Target Names WD1057+719 WAVE REJ1614-085 ------------------------------------------------------------------------------------------------------------------------------------