8179( 3) - 10/12/99 13:29 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8179 Version: 3 Check-in Date: 04-Feb-1999 12:35:03 1.Proposal Title: THE COMPOSITION AND EVOLUTION OF EXTREMELY HOT DA WHITE DWARFS ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 8 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Martin Barstow University of Leicester CoI: Dr Jay Holberg University of Arizona N CoI: Dr Matthew Burleigh University of Leicester N CoI: Dr Ivan Hubeny Goddard Space Flight Center N CoI: Dr Ralf Napiwotzki Dr. Remeis-Sternwarte N ------------------------------------------------------------------------------------ 5. Abstract We propose high S/N (15:1 to 30:1) STIS far UV observations of the hottest known DA white dwarfs. With temperatures in the range 70, 000-130, 000K, these stars represent an important but little understood link between the H-rich central stars of planetary nebulae (CPN) and the general population of DA white dwarfs. Stellar temperatures are extremely difficult to determine in this range and depend upon knowledge of the photospheric composition, which is also a mystery. Consequently, their relationship to the cooler DA stars remains undefined. Far UV measurements of the abundances of heavy elements are essential for an ultimate determination of the stellar temperature. Coupling STIS data with an analysis of the Lyman lines obtained with planned FUSE observations, it will be possible to determine the physical parameters of these objects and finally track their evolution along the DA cooling sequence. In addition, we will search for evidence of mass outflow, in the form of blueward asymmetries in the heavy element line profiles, which is believed to cause departures from the compositions predicted by radiative levitation theory but which has been observed in only two DA white dwarfs. ------------------------------------------------------------------------------------ 8179( 3) - 10/12/99 13:29 - [ 2] Observations Description ------------------------ Real Time Justification ----------------------- section*The need for HST The white dwarfs we are proposing are the brightest known of the class of young extremely hot DAs. They were mainly too faint for practical observation with IUE in echelle mode, which in any case is no longer available. REJ1738 and REJ0558 had been included in the final IUE programme, but were very close to the limit for practical exposures and, in the event, were not observed due to technical problems with the spacecraft. However, all these objects are easily observable with the STIS/FUV. Consequently we have gauged the required exposure times to match the S/N we have successfully achieved with IUE observations of the brighter and cooler DAs such as REJ2214- 492 and G191-B2B. This is an average S/N ~ 15:1 and, at the peak of ~ 1350Angstrom, will approach the practical 30:1 limit expected for operations of the STIS MAMA detectors. At this level, our IUE and STIS cycle 7 experience demonstrates we can determine abundances of important elements such as C, N, O, Si, Fe and Ni, and detect mass loss. Hence, the programme is very well matched to the capabilities of STIS/FUV. The spectral coverage (1150-1700Angstrom), spectral configuration (STIS/FUV + E140M) and signal-to-noise (average 15:1, peak 30:1) are identical for each target. Exposure times and signal-to-noise predictions were calculated using the WWW STIS exposure calculator with suitable synthetic model atmosphere spectra created with TLUSTY. The required exposures (in minutes) are summarised in table 1. REJ1738+665, WD2218+706 and EGB1 lie in the continuous viewing zone. PG0948+534 is close to the edge of the northern CVZ region, and may be observable as a CVZ target but it is not possible to confirm this from the handbook information. If it can, then the observing time needed will be reduced by one orbit. We have been awarded Cycle 1 FUSE time to observe all but one of these targets. The exception is Ton 21, which is already included as project team target and not available for the GO programme. However, we note that FUSE data has a short 6 month proprietary period before becoming public. These FUSE observation will give us access to the Lyman lines for determination of the stellar temperature and, therefore, complement the abundance information that will be obtained with our HST observations. There are no time-dependent or other requirements on either the FUSE or STIS observations of each target. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 8179( 3) - 10/12/99 13:29 - [ 3] Data Distribution Paper Products: NO Media: ELECTRONIC Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 8179( 3) - 10/12/99 13:29 - [ 4] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 REJ1738+665 STAR, DA RA=17H38M02.46S +/- 0.3S, J2000 V = 14.6 DEC=+66D53'47.8" +/- 0.3", PLATE F(1250)=1.1+/-0.1e-12 -ID=01H3 Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) B1983.29 0.0 0.0 0.0 2 TON21 STAR, DA RA=09H42M50.72S +/- 0.3S, J2000 V = 14.6 DEC=+26D00'59.93" +/- 0.3", F(1250)=1.1+/-0.2e-12 PLATE-ID=01X3 Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) B1983.04 0.0 0.0 0.0 3 REJ0558-376 STAR, DA RA=05H58M14.53S +/-0.3S, DEC=- J2000 V = 14.4 37D34'24.82" +/-0.3", PLATE- F(1250)=1.1+/-0.2e-12 ID=01D6 Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) B1976.96 0.0 0.0 0.0 4 WD2218+706 STAR, DA RA=22H19M33.79S +/-0.3S, J2000 V = 15.4 DEC=+70D56'03.99" +/-0.3", PLATE F(1250)=5.0+/-0.5e-13 -ID=003H Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) B1983.68 0.0 0.0 0.0 5 PG0948+534 STAR, DA RA=09H51M25.86S +/-0.3S, J2000 V = 15.3 DEC=53D09'30.66" +/-0.3", PLATE- F(1250)=6.0+/-0.6e-13 ID=0009 Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) B1983.14 0.0 0.0 0.0 8179( 3) - 10/12/99 13:29 - [ 5] Visit: 01 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 11 REJ1738+665 STIS/C ACQ F28X50L MIRROR 1 1 S ONBOARD ACQ FOR 12 CD P ------------------------------------------------------------------------------------------------------------------------------------ 12 REJ1738+665 STIS/F ACCUM 0.2X0.2 E140M 1425 2 4980 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 8179( 3) - 10/12/99 13:29 - [ 6] 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 ------------------------------------------------------------------------------------------------------------------------------------ 21 TON21 STIS/C ACQ F28X50L MIRROR 1 1 S ONBOARD ACQ FOR 22-24 CD P ------------------------------------------------------------------------------------------------------------------------------------ 22 TON21 STIS/F ACCUM 0.2X0.2 E140M 1425 1 2325 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 23 TON21 STIS/F ACCUM 0.2X0.2 E140M 1425 1 2923 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 24 TON21 STIS/F ACCUM 0.2X0.2 E140M 1425 1 2923 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 8179( 3) - 10/12/99 13:29 - [ 7] Visit: 03 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 ------------------------------------------------------------------------------------------------------------------------------------ 31 REJ0558-376 STIS/C ACQ F28X50L MIRROR 1 1 S ONBOARD ACQ FOR 32-34 CD P ------------------------------------------------------------------------------------------------------------------------------------ 32 REJ0558-376 STIS/F ACCUM 0.2X0.2 E140M 1425 1 2379 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 33 REJ0558-376 STIS/F ACCUM 0.2X0.2 E140M 1425 1 2977 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 34 REJ0558-376 STIS/F ACCUM 0.2X0.2 E140M 1425 1 2977 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 8179( 3) - 10/12/99 13:29 - [ 8] Visit: 04 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 41 WD2218+706 STIS/C ACQ F28X50L MIRROR 1 1 S ONBOARD ACQ FOR 42 CD P ------------------------------------------------------------------------------------------------------------------------------------ 42 WD2218+706 STIS/F ACCUM 0.2X0.2 E140M 1425 3 5160 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 8179( 3) - 10/12/99 13:29 - [ 9] Visit: 05 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 ------------------------------------------------------------------------------------------------------------------------------------ 51 PG0948+534 STIS/C ACQ F28X50L MIRROR 1 1 S ONBOARD ACQ FOR 52-55 CD P ------------------------------------------------------------------------------------------------------------------------------------ 52 PG0948+534 STIS/F ACCUM 0.2X0.2 E140M 1425 1 2513 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 53 PG0948+534 STIS/F ACCUM 0.2X0.2 E140M 1425 1 3110 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 54 PG0948+534 STIS/F ACCUM 0.2X0.2 E140M 1425 1 3110 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 55 PG0948+534 STIS/F ACCUM 0.2X0.2 E140M 1425 1 3110 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 8179( 3) - 10/12/99 13:29 - [ 10] Summary Form for Proposal 8179 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50LP 0.2X0.2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CVZ ONBOARD ACQ FOR 12 ONBOARD ACQ FOR 22-24 ONBOARD ACQ FOR 32-34 ONBOARD ACQ FOR 42 ONBOARD ACQ FOR 52-55 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR E140M ------------------------------------------------------------------------------------------------------------------------------------ Target Names REJ1738+665 TON21 REJ0558-376 WD2218+706 PG0948+534 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 1425 ------------------------------------------------------------------------------------------------------------------------------------