8637( 2) - 12/20/00 16:39 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8637 Version: 2 Check-in Date: 02-Mar-2000 14:04:29 1.Proposal Title: Distance to the prototype WD showing signatures of a super-hot wind ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 9 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Klaus Werner Universitat Tubingen, Institut fur Astronomie & Astrophysik CoI: Dr. Stefan Dreizler Universitaet Tuebingen, Institut fuer N Astronomie und Astrophysik CoI: Dr. Lars Koesterke Universitaet Potsdam, Institut fuer Physik N CoI: Dr. Ralf Napiwotzki Universitaet Erlangen-Nuernberg, N Sternwarte Bamberg ------------------------------------------------------------------------------------ 5. Abstract We propose to determine the distance to the prototype of a new class of hot white dwarfs (WD). Their optical spectra reveal absorption lines from ultra-high ionized metals (e.g. IonOVIII), a phenomenon never observed before in any astronomical object. The occurrence of such features requires temperatures in the order of 10^6 K, far in excess of the stellar T_ eff. The asymmetric line profiles suggest formation in a rapidly accelerating high-speed wind (10, 000 km s^-1). These stars represent the most convincing proof for on- going mass-loss from WDs. We have demonstrated that a large fraction of hot WDs shows this phenomenon, concluding that perhaps all WD go through this evolutionary stage. For the prototype we will determine stellar parameters and possible consequences of the mass-loss for WD evolution on hand of detailed NLTE modeling. The distance to the star is an essential prerequisite for this. We propose to derive the distance spectroscopically by determination of spectral type and luminosity class of the cool companion of the WD. ------------------------------------------------------------------------------------ 8637( 2) - 12/20/00 16:39 - [ 2] Observations Description ------------------------ We plan to perform long-slit low dispersion spectroscopy of the cool companion of \hsnull\ in the G750L configuration. This covers the range 5250-- 10300Angstrom\ and enables the determination of the spectral type. The determination of the luminosity class is essential, because it is well known that evolved low mass stars often have companions which have left the main sequence. The luminosity class can be derived from the strength of several spectral features, by comparison with moderate-resolution (5Angstrom) spectral standards given in Allen & Strom (1995), e.g.\ the CaH band at 6974Angstrom\ and the IonCaII line at 8542Angstrom. We used the STIS Exposure Time Calculator to determine the exposure time necessary to achieve S/N ~ 30 (2200 sec) for a Kurucz K7 model atmosphere. In order to estimate the absolute flux level we used our JHK photometry (Napiwotzki 1997), (H=17.0), and subtracted the hot primary contribution assuming a Rayleigh-Jeans flux distribution with V=16.2. We perform target acquisition on the optically brighter hot primary and perform an offset in order to put the cool secondary into the slit. Offset coordinates can be determined from our IR images (Fig. 4). The observation can be performed during one orbit. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 8637( 2) - 12/20/00 16:39 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HS0713+3958A STAR, WDO, STAR, K V-IV RA=07H 17M 2.67S +/- 0.1", J2000 V = 16.2+/-0.2 DEC=39D 53' 23.6" +/- 0.1", PLATE-ID=00VU Coordinate Source: GSC_SURVEY_PLATE Comments: binary system, acquisition on primary (hot DO White Dwarf), subsequent offset on secondary (K-type) 2 HS0713+3958B STAR, WDO, STAR, K V-IV RA-OFF=-0.00143S+/- 0.00253S, J2000 V = 18.4+/-0.5 DEC-OFF=0.98599999999999999"+/- 0.05", FROM 1, PLATE-ID=00VU Coordinate Source: IMAGE_TIED_TO_GSC_FRAME Comments: binary system, acquisition on primary (hot DO White Dwarf), subsequent offset on secondary (K-type) 8637( 2) - 12/20/00 16:39 - [ 4] Visit: 01 Visit Priority: Visit Requirements: ORIENT 120D TO 150D ORIENT 300D TO 330D On Hold Comments: Additional Comments: none Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 HS0713+3958 STIS/C ACQ F28X50L MIRROR 1 2 S A CD P Comments: primary component, S/N=40 (default) ------------------------------------------------------------------------------------------------------------------------------------ 30 HS0713+3958 STIS/C ACCUM 52X0.2 G750L 7751 1 2460 S B CD Comments: none ------------------------------------------------------------------------------------------------------------------------------------ 60 CCDFLAT STIS/C ACCUM 52X0.2 G750L 7751 2 DEF END ORBIT CD Comments: none ------------------------------------------------------------------------------------------------------------------------------------ 8637( 2) - 12/20/00 16:39 - [ 5] Summary Form for Proposal 8637 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50LP 52X0.2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 120D TO 150D ORIENT 300D TO 330D END ORBIT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G750L ------------------------------------------------------------------------------------------------------------------------------------ Target Names HS0713+3958A HS0713+3958B CCDFLAT ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 7751 ------------------------------------------------------------------------------------------------------------------------------------