6654( 9) - 07/09/96 10:37 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6654 Version: 9 Check-in Date: 09-Jul-1996 10:20:00 1.Proposal Title: Ultraviolet Spectroscopy of Hot DB White Dwarfs ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle HOT STARS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: FRANCOIS WESEMAEL UNIVERSITE DE MONTREAL CoI: Pierre Bergeron Bell Northern Research N CoI: Alain Beauchamp C.A.E. Electronics, Ltd. N ------------------------------------------------------------------------------------ 6. Abstract Any tentative explanation of the origin of the various families of white dwarf stars requires first a complete understanding of their basic physical properties (effective temperature, surface gravity, surface composition). In order to refine the calibration of the effective temperature scale of the hot, helium-line (DB) white dwarfs, we propose to secure FOS/GHRS energy distributions in the 1200--3250 Angstrom\ range for two of these stars. This includes the hottest known DB star, WD 0112+104, as well as one hot, pulsating (V777 Her) star. The specific goal of these observations is twofold: i) To derive an accurate ultraviolet temperature, T^UV_ eff, which can be compared to that derived from our detailed analysis of the optical spectrum. Because we believe that existing discrepancies between current estimates of these quantities are related to the presence of small traces of hydrogen in the photosphere, which remain invisible in the optical spectrum, we also intend ii) to use the observed Ly-alpha\ region to estimate, or constrain, the hydrogen abundance in these objects. Limits are not available from the ground for DB stars above (T_ eff >~ 20,000 K), as the Balmer lines fade rapidly for increasingly lower hydrogen abundances. By contrast, the wings of Ly-alpha\ remain useful for detecting hydrogen even at low abundance values. ------------------------------------------------------------------------------------ 6654( 9) - 07/09/96 10:37 - [ 2] Observations Description ------------------------ Medium-resolution spectrophotometric observations at S/N (square)uig 20 of the energy distribution of hot DB stars between 1600 and 3250 Angstrom\\ will be obtained with a combination of FOS/RD, G190H and G270H dispersers, and high throughput ( 4.3) aperture. This combination will allow, furthermore, coverage of the He II Lambda1640 transition at (square)uig 1.5 Angstrom\\ resolution. For the blue data, which include observations of Ly-alpha, we have explored two possibilities: FOS/BL+G130H through aperture 4.3; and GHRS Side 1+G140L+LSA in the 1100--1385 and 1385--1670 Angstrom\\ ranges. While less efficient, the latter combination was considered more appropriate, in that the 1.74 arcsec square LSA is large enough for accurate spectrophotometry (95\\% throughput), but small enough to reduce geocoronal Ly-alpha\\ contamination. Because the geocoronal component is expected to be superposed onto interstellar absorption, our analysis will be restricted to the wings of the photospheric Ly-alpha\\ profile. As an example, we give below the details of our exposure-time estimates for the brightest of our objects, WD 0112+104 (V=15.36), assuming S/N=20 for all spectra: smallskip # \\quad&& # \\quad noalign noalign Configuration & f_Lambda & S_lambda^-1 & N_Lambda & t_exp & ergs cm^-2, s^-1, Angstrom^-1 && cts, s^-1, diode^-1 & noalign noalign noalign HRS/G140L LSA Lambda_o=1285Angstrom\\ & 1.1* 10^-13 & 6.3* 10^-14 & 1.76 & 228 s HRS/G140L LSA Lambda_o=1530Angstrom\\ & 7.6* 10^-14 & 1.3* 10^-13 & 0.58 & 688 s FOS/RD G190H & 4.7* 10^-14 & 1.1* 10^-14 & 4.15 & 97 s FOS/RD G270H & 1.7* 10^-14 & 1.9* 10^-15 & 9.30 & 43 s noalign noalign Real Time Justification ----------------------- Optical spectra for our two targets have already been secured at the Steward Observatory 2.3m telescope, and have been analyzed. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6654( 9) - 07/09/96 10:37 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 WD0112+104 STAR,DB RA=1H14M37.68S+/- J2000 V = 15.36 0.01S,DEC=10D41'05.45"+/- B-V = -0.14 0.1",PLATE-ID=00GR F(1700)=6.8e-14 2 WD1654+160 STAR,DB RA=16H56M57.52S+/- J2000 V = 16.5+/-0.3 0.01S,DEC=15D56'26.41"+/- B-V = -0.14 0.1",PLATE-ID=02D2 F(1700)=1.9e-14 6654( 9) - 07/09/96 10:37 - [ 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 WD0112+104 FOS/RD ACQ/BIN 4.3 MIRROR 1 2.0 S ONBOARD ACQuisition FOR 2 ARY ------------------------------------------------------------------------------------------------------------------------------------ 2 WD0112+104 FOS/RD ACQ/PEA 0.3 MIRROR SEARCH-SIZE-X=5,SEARCH-SIZE-Y=5, 1 3.0 S ONBOARD ACQuisition FOR K SCAN-STEP-X=0.11,SCAN-STEP-Y=0.11 3-6 Comments: FOR NOMINAL 0.08" CENTERING ACCURACY ------------------------------------------------------------------------------------------------------------------------------------ 3 WD0112+104 FOS/RD ACCUM 4.3 G190H 1 400 S ------------------------------------------------------------------------------------------------------------------------------------ 4 WD0112+104 FOS/RD ACCUM 4.3 G270H 1 150 S ------------------------------------------------------------------------------------------------------------------------------------ 5 WD0112+104 HRS ACCUM 2.0 G140L 1285 1 652.8 S ------------------------------------------------------------------------------------------------------------------------------------ 6 WD0112+104 HRS ACCUM 2.0 G140L 1530 2 598.4 S ------------------------------------------------------------------------------------------------------------------------------------ 6654( 9) - 07/09/96 10:37 - [ 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 WD1654+160 FOS/RD ACQ/BIN 4.3 MIRROR 1 5.0 S ONBOARD ACQuisition FOR 2 ARY ------------------------------------------------------------------------------------------------------------------------------------ 2 WD1654+160 FOS/RD ACQ/PEA 0.3 MIRROR SEARCH-SIZE-X=5,SEARCH-SIZE-Y=5, 1 8.0 S ONBOARD ACQuisition FOR K SCAN-STEP-X=0.11,SCAN-STEP-Y=0.11 3-6 Comments: FOR NOMINAL 0.08" CENTERING ACCURACY ------------------------------------------------------------------------------------------------------------------------------------ 3 WD1654+160 FOS/RD ACCUM 4.3 G190H 1 340 S ------------------------------------------------------------------------------------------------------------------------------------ 4 WD1654+160 FOS/RD ACCUM 4.3 G270H 1 150 S ------------------------------------------------------------------------------------------------------------------------------------ 5 WD1654+160 HRS ACCUM 2.0 G140L 1285 2 707.2 S ------------------------------------------------------------------------------------------------------------------------------------ 6 WD1654+160 HRS ACCUM 2.0 G140L 1530 5 652.8 S ------------------------------------------------------------------------------------------------------------------------------------ 6654( 9) - 07/09/96 10:37 - [ 6] Summary Form for Proposal 6654 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOS/RD HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/BINARY ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SEARCH-SIZE-X=5 SEARCH-SIZE-Y=5 SCAN-STEP-X=0.11 SCAN-STEP-Y=0.11 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category HOT STARS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQuisition FOR 2 ONBOARD ACQuisition FOR 3-6 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G190H G270H G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names WD0112+104 WD1654+160 ------------------------------------------------------------------------------------------------------------------------------------