6571( 4) - 07/16/96 11:10 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6571 Version: 4 Check-in Date: 16-Jul-1996 11:05:50 1.Proposal Title: Carbon and Convective Mixing in Hot Helium Rich White Dwarf Stars ------------------------------------------------------------------------------------ 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 key to understanding main sequence evolution is hidden in the detailed knowledge of the interiors of white dwarfs, the endpoints of stellar evolution. Unfortunately, we do not understand these objects. We find structural differences among the two major groups of white dwarfs (hydrogen vs helium photospheres) that demand differences in origin which are not clearly understood by our current models. In 1992, HST obtained high quality, high resolution spectra of the well studied helium (DB) white dwarf PG1645+325 (GD358), a multiperiodic g-mode pulsator, detecting CII (1335 Angstrom) and HeII (1640Angstrom). Our results imply a thin helium layer mass, in agreement with the asteroseismology (10^-6\ rmMSUN) and in disagreement with the conventional wisdom of stellar evolution. We propose using carbon to probe the envelope structure of the hotter DB white dwarfs. ------------------------------------------------------------------------------------ Observations Description ------------------------ The observations will be done with GHRS in ACCUM mode, centered on 1335\\ Angstrom, and using the large science aperture. We have calculated the exposure times using previous observations of PG1645+325 as a flux model. The exposure times are calculated to give a signal to noise ratio of ~20. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6571( 4) - 07/16/96 11:10 - [ 2] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6571( 4) - 07/16/96 11:10 - [ 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 Comments: Visits 2 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 6571( 4) - 07/16/96 11:10 - [ 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 2-3 Comments: STEP-TIME=2.0 sec ------------------------------------------------------------------------------------------------------------------------------------ 2 WAVE HRS ACCUM SC2 G160M 1335 SPYBAL=YES 1 DEF ------------------------------------------------------------------------------------------------------------------------------------ 3 GD190 HRS ACCUM 2.0 G160M 1335 FP-SPLIT=STD,STEP-PATT=DEF 2 2145.0 ------------------------------------------------------------------------------------------------------------------------------------ 6571( 4) - 07/16/96 11:10 - [ 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 2-3 Comments: STEP-TIME=6.0 sec ------------------------------------------------------------------------------------------------------------------------------------ 2 WAVE HRS ACCUM SC2 G160M 1335 SPYBAL=YES 1 DEF ------------------------------------------------------------------------------------------------------------------------------------ 3 PG0112+104 HRS ACCUM 2.0 G160M 1335 FP-SPLIT=STD,STEP-PATT=DEF 2 1919.9 ------------------------------------------------------------------------------------------------------------------------------------ 6571( 4) - 07/16/96 11:10 - [ 6] Summary Form for Proposal 6571 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SEARCH-SIZE=3 SPYBAL=YES STEP-PATT=DEF FP-SPLIT=STD ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category HOT STARS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 2 ONBOARD ACQuisition FOR 2-3 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N2 G160M ------------------------------------------------------------------------------------------------------------------------------------ Target Names GD190 WAVE PG0112+104 ------------------------------------------------------------------------------------------------------------------------------------