6656( 5) - 07/16/96 14:00 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6656 Version: 5 Check-in Date: 16-Jul-1996 13:57:49 1.Proposal Title: Hydrogen, Interstellar Accretion, and Hot Helium Rich White Dwarfs ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle HOT STARS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: JUDI PROVENCAL UNIVERSITY OF DELAWARE CoI: Prof. Harry Shipman University of Delaware N ------------------------------------------------------------------------------------ 6. Abstract The study of white dwarf structure provides valuable insights into the final stages of stellar evolution. Recently, rapid developments in UV spectroscopy have altered our understanding of these simplest of stars. It is now clear that hydrogen (DA) and helium (DB) white dwarfs follow different evolutionary paths. While it appears that once a DA is formed, it remains a DA throughout its evolution, our understanding of DB evolution is particularly sketchy. About 20\% of all DBs contain traces of hydrogen, and we observe a gap in DB distribution between 30,000\ rmK< rmT_eff<45,000\ rmK. Current theory predicts that, at these temperatures, hydrogen floats to the surface, masking the DB white dwarf beneath a thin hydrogen photosphere. In 1992, HST obtained high resolution spectra, centered on 1215\ Angstrom, of the prototype DBV PG1645+325 (GD358), detecting broad shallow absorption wings of hydrogen surrounding the geocoronal emission. Initial results indicate that PG1645+325, rmT_eff=\ 27,000 K, does not have enough hydrogen to have been a DA in the DB gap. We propose a search for hydrogen in hot DB white dwarfs, to test theories of DB evolution and address the question of the uniqueness of PG1645+325. ------------------------------------------------------------------------------------ 6656( 5) - 07/16/96 14:00 - [ 2] Observations Description ------------------------ The observations will be done with GHRS in ACCUM mode, centered on 1215\\ Angstrom, using the small science aperture to reduce geocoronal emission. We have calculated the exposure times of the other targets using previous observations of PG1645+325 as a flux model. The exposure times are calculated to give a signal to noise ratio of ~20 (see table). We have submitted a second proposal addressing carbon pollution and convective dredgeup in the hotter DBs, also motivated by earlier HST observations of PG1645+325. Both these proposals deal with the atmospheric structure of DB white dwarfs, yet we felt we were exploring a different aspect of the problem with each proposal. We opted for individual proposals because we felt we could learn something interesting from each separately. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6656( 5) - 07/16/96 14:00 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 GD190 STAR,DB RA=15H 44M 19.45S +/- J2000 V = 14.72 0.030S,DEC=+18D 06' 46.38" +/- B-V = -0.10 0.40", PLATE-ID=00GM Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1982.384033 0.001 -0.113 0.0 2 PG0112+104 STAR, DB RA=01H 14M 37.68S +/- J2000 V = 15.33 0.030S,DEC=+10D 41' 05.45" +/- B-V = -0.03 0.40", PLATE-ID=00GR Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1982.795043 0.0 0.0 0.0 6656( 5) - 07/16/96 14:00 - [ 4] Visit: 01 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 GD190 HRS ACQ 2.0 MIRROR-N2 SEARCH-SIZE=3 1 18.0 S ONBOARD ACQ FOR 2 ONBOARD ACQuisition FOR 2 ------------------------------------------------------------------------------------------------------------------------------------ 2 GD190 HRS ACQ/PEA 0.25 MIRROR-N2 SEARCH-SIZE=5 1 50.0 S ONBOARD ACQ FOR 3-4 KUP ONBOARD ACQuisition FOR 3-4 ------------------------------------------------------------------------------------------------------------------------------------ 3 WAVE HRS ACCUM SC2 G160M 1215 SPYBAL=YES 1 DEF ------------------------------------------------------------------------------------------------------------------------------------ 4 GD190 HRS ACCUM 0.25 G160M 1215 FP-SPLIT=STD,STEP-PATT=DEF 2 1740.8 ------------------------------------------------------------------------------------------------------------------------------------ 6656( 5) - 07/16/96 14:00 - [ 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 PG0112+104 HRS ACQ 2.0 MIRROR-N2 SEARCH-SIZE=3 1 54.0 S ONBOARD ACQ FOR 2 ONBOARD ACQuisition FOR 2 Comments: STEP-TIME=6.0 sec ------------------------------------------------------------------------------------------------------------------------------------ 2 PG0112+104 HRS ACQ/PEA 0.25 MIRROR-N2 SEARCH-SIZE=5 1 150.0 S ONBOARD ACQ FOR 3-4 KUP ONBOARD ACQuisition FOR 3-4 ------------------------------------------------------------------------------------------------------------------------------------ 3 WAVE HRS ACCUM SC2 G160M 1215 SPYBAL=YES 1 DEF ------------------------------------------------------------------------------------------------------------------------------------ 4 PG0112+104 HRS ACCUM 0.25 G160M 1215 FP-SPLIT=STD,STEP-PATT=DEF 2 2828.8 ------------------------------------------------------------------------------------------------------------------------------------ 6656( 5) - 07/16/96 14:00 - [ 6] Summary Form for Proposal 6656 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAKUP ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SEARCH-SIZE=3 SEARCH-SIZE=5 SPYBAL=YES STEP-PATT=DEF FP-SPLIT=STD ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category HOT STARS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 2 ONBOARD ACQuisition FOR 2 ONBOARD ACQ FOR 3-4 ONBOARD ACQuisition FOR 3-4 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N2 G160M ------------------------------------------------------------------------------------------------------------------------------------ Target Names GD190 WAVE PG0112+104 ------------------------------------------------------------------------------------------------------------------------------------