8649( 3) - 11/15/00 11:54 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8649 Version: 3 Check-in Date: 15-Nov-2000 11:53:38 1.Proposal Title: Probing Stellar Interiors Via Convective Dredge-up in DQ White Dwarfs ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 9 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Judith Provencal University of Delaware CoI: Prof. Harry Shipman University of Delaware N CoI: Prof. James MacDonald University of Delaware N ------------------------------------------------------------------------------------ 5. Abstract The composition and structure of white dwarf stars contain a wealth of information about processes occurring in contemporary main sequence stars like our sun. We use this information to build theoretical models placing limits on the star formation history and age of the Galactic disk. One of the largest uncertainties in our models is the unknown core composition of a white dwarf. We generally assume a mixture of carbon and oxygen, but the exact ratio is unknown. This uncertainty introduces a 20\ dwarfs offer our only opportunity to directly observe the actual carbon/oxygen ratio in a white dwarf core. DQs are are otherwise normal helium-rich stars displaying carbon features in their spectra. The observed carbon in these objects results from dredge-up of the underlying core by the helium convection zone. Recent theoretical work argues that oxygen should also be present in detectable amounts in the more massive DQ stars. We propose a modest investment of HST time to determine for the first time whether a white dwarf core contains a substantial quantity of oxygen. We will search for trace amounts of oxygen in the atmosphere of a massive DQ as an important step towards resolving this question. ------------------------------------------------------------------------------------ 8649( 3) - 11/15/00 11:54 - [ 2] Observations Description ------------------------ The observations of our target will be done with STIS in ACCUM mode using the G140M grating and the MAMA detectors, centered on 1321 rmAngstrom. We expect features rm~ \ 2-3 Angstrom wide, well within the capabilities of this instrument and grating combination. The spectral range will also cover CII 1335 and interstellar lines of silicon. Our desire for higher resolution is driven by the need to obtain accurate velocities to distinguish interstellar and photospheric features. The white dwarf velocities are well established from optical observations (Provencal et al. 1998, Wegner & Koester 1985)). Both targets are faint. G35-26 (rmm_v=16.7) requires 9 orbits to reach a S/N of rm~20 and WD172+56 requires 5. These exposure calculations were done using the HST standard star LDS749B as a model. LDS749B is a helium white dwarf with a similar effective temperature. Real Time Justification ----------------------- WD1728+56 can be scheduled during a CVZ opportunity. This will maximize the use of HST time on this relatively faint object. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 8649( 3) - 11/15/00 11:54 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 WD0203+20 STAR RA=02H 5M 49.94S +/- 0S, DEC=20D J2000 V = 16.7+/-0.5 57' 11.9" +/- 0", PLATE-ID=03OO Coordinate Source: GUIDE_STAR_CATALOG Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1983.680053 -0.0142 -0.278 0.0 2 WD1728+560 STAR RA=17H 28M 56.5S +/- 0S, DEC=55D J2000 V = 16.1+/-0.5 58' 18.8" +/- 0", PLATE-ID=00T6 Coordinate Source: GUIDE_STAR_CATALOG Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1983.354003 -0.0116 0.250 0.0 8649( 3) - 11/15/00 11:54 - [ 4] Visit: 01 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 WD0203+20 STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 0.8 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 12 WD0203+20 STIS/F ACCUM 52X0.2 G140M 1321 5 2400 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 8649( 3) - 11/15/00 11:54 - [ 5] Visit: 02 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 WD0203+20 STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 0.8 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 12 WD0203+20 STIS/F ACCUM 52X0.2 G140M 1321 4 2400 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 8649( 3) - 11/15/00 11:54 - [ 6] Visit: 03 Visit Priority: Visit Requirements: CVZ ON HOLD On Hold Comments: Schedule either visit 3 or visit 13. Visit 3 is preferred, but visit 13 may be used as an alternate if visit 3 would otherwise be long delayed while awaiting a CVZ opportunity. 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 WD1728+560 STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 0.6 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 12 WD1728+560 STIS/F ACCUM 52X0.2 G140M 1321 5 5169 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 8649( 3) - 11/15/00 11:54 - [ 7] Visit: 13 Visit Priority: Visit Requirements: VISIBILITY INTERVAL 90 M ON HOLD On Hold Comments: Schedule either visit 3 or visit 13. Visit 3 is preferred, but visit 13 may be used as an alternate if visit 3 would otherwise be long delayed while awaiting a CVZ opportunity. 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 WD1728+560 STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 0.6 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 12 WD1728+560 STIS/F ACCUM 52X0.2 G140M 1321 5 5169 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 8649( 3) - 11/15/00 11:54 - [ 8] Summary Form for Proposal 8649 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50LP 52X0.2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CVZ ON HOLD VISIBILITY INTERVAL 90 M ON HOLD ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G140M ------------------------------------------------------------------------------------------------------------------------------------ Target Names WD0203+20 WD1728+560 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 1321 ------------------------------------------------------------------------------------------------------------------------------------