6454( 3) - 02/15/96 09:12 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6454 Version: 3 Check-in Date: 15-Feb-1996 09:05:11 1.Proposal Title: UV spectroscopy of a DAO white dwarf showing signatures of an extremely hot wind ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle HOT STARS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Klaus Werner Universitaet Potsdam CoI: Stefan Dreizler Universitaet Kiel N CoI: Wolf-R. Hamann Universitaet Potsdam N CoI: Ulrich Heber Universitaet Erlangen--Nuernberg N CoI: Ralf Napiwotzki Universitaet Erlangen--Nuernberg N CoI: Thomas Rauch Universitaet Potsdam N ------------------------------------------------------------------------------------ 6. Abstract HS2115+1148 belongs to a small group of peculiar white dwarfs detected within the framework of follow--up spectroscopy of faint blue stars selected from the Hamburg Schmidt survey. The spectra of these stars exhibit shallow metal absorption ( lines from ultrahighly excited ionization stages (CV, CVI / NVI, NVII / OVII, OVIII / NeIX, NeX) with ionization energies ranging from 392eV to 1362eV, far too high for a photospheric origin even for the hottest stars known. Due to the blue shift and asymmetric shape of these lines we proposed that they are formed in a stellar wind. The underlying photospheric spectra resemble that of hot helium rich (DO) white dwarfs in five cases. Recently we detected this phenomenon also in a single hydrogen rich white dwarf with traces of helium (HS2115+1148), making this star unique among the peculiar white dwarfs. The number ratio of these stars to ordinary hot white dwarfs suggests that this phenomenon might be common at the beginning of the white dwarf cooling sequence. Depending on the duration and the mass--loss rate, cooling time scales and luminosity functions of white dwarfs could be affected with serious consequences for our understanding of the late stages of low--mass star evolution. The proposed HST observation is needed to verify the nature of this star by detailed spectrum synthesis in order to precisely determine stellar and wind parameters. ------------------------------------------------------------------------------------ 6454( 3) - 02/15/96 09:12 - [ 2] Observations Description ------------------------ We propose to observe HS2115+1148 with the GHRS in two wavelength regions. Generally, a resolution of about 1Angstrom is sufficient, because the lines are expected to be broad like the optical lines. We therefore want to use the low resolution grating G140L. A S/N > 20 over the whole wavelength range is aimed at. 1150- 1436Angstrom, t_exp=76 min with grating G140L. According to Tab.1 an OVIII and CVI line will be detected. 1494-1781Angstrom, t_exp=96 min with grating G140L, covering numerous high ionization lines. The first wavelength range can be exposed during two orbits after guide star and target acquisition. The second wavelength range is exposed during the 3rd and 4th orbits after re- acquisition. The number of orbits for this whole proposal is then 4. Table 2 summarizes our exposure time estimates. The UV fluxes of HS2115+1148 are estimated from the IUE low resolution spectrum of \\hs. The UV range is in the Rayleigh--Jeans tail of both stars. begintableh labelTexp caption Summary of proposed exposures with G140L. centering c wavelength& F_Lambda (IUE) /10^-14 & grating & sensitivity & count rate & t_ exp & (S/N) , Angstrom & erg/cm^2/sec/Angstrom & & 10^11 & per sec & minutes & minimum, 1150 & 6.7 & G140L &21. & 0.14 & 76 & 25 , 1700 & 2.5 & G140L &32. & 0.42 & 96 & 22 , endtabular endtable Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6454( 3) - 02/15/96 09:12 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HS2115+1148 STAR,DA RA=21H 18M 18.73S +/- J2000 V = 16.8+/-0.2 0.1S,DEC=12D 01' 31.41" +/- B-V = -0.3+/-0.1 0.1",PLATE-ID=02V2 6454( 3) - 02/15/96 09:12 - [ 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 HS2115+1148 HRS ACQ 2.0 MIRROR-N1 SEARCH- 1 23.4S ONBOARD ACQ FOR 2 SIZE=3,BRIGHT=R ETURN Comments: STEP-TIME=2.6S, EXPECT 400 CNTS ------------------------------------------------------------------------------------------------------------------------------------ 2 HS2115+1148 HRS ACCUM 2.0 G140L 1150- FP- 1 4243.2S 1436 SPLIT=STD,COMB= FOUR,DOPPLER=ON ------------------------------------------------------------------------------------------------------------------------------------ 3 HS2115+1148 HRS ACCUM 2.0 G140L 1494- FP- 1 5440.0S 1781 SPLIT=STD,COMB= FOUR,DOPPLER=ON ------------------------------------------------------------------------------------------------------------------------------------ 6454( 3) - 02/15/96 09:12 - [ 5] Summary Form for Proposal 6454 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SEARCH-SIZE=3 BRIGHT=RETURN DOPPLER=ON COMB=FOUR ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category HOT STARS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 2 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N1 G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names HS2115+1148 ------------------------------------------------------------------------------------------------------------------------------------