6727( 10) - 07/19/96 16:14 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6727 Version: 10 Check-in Date: 19-Jul-1996 16:10:40 1.Proposal Title: A Unique Test of Asteroseismology: the DBV GD358 ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle HOT STARS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: DONALD E. WINGET UNIVERSITY OF TEXAS CoI: S.O. Kepler Universidade Federal do Rio Grande do Sul N ------------------------------------------------------------------------------------ 6. Abstract An improved understanding of the white dwarf stars has a great potential in both physics and astronomy. Determination of the basic physical parameters of the white dwarf stars will help us realize that potential; asteroseismology is the key. We can use asteroseismology to constrain the stellar structure and evolution, including the stellar mass and even the stellar distance if we can determine the pulsation indices (k,\ell,m) of the non-radial g-mode light variations observed in compact pulsators. We made tentative identifications for GD 358 using a method based on the frequency distribution of consecutive radial overtone g-modes. A comparison of the amplitude of the pulsation between the optical and the UV proves to be another independent method to identify the pulsation indices. Our project is to apply both methods to GD358. For the HST observations we will use the FOS blue digicon with the G160L grating in RAPID readout mode to obtain time-resolved spectrophotometry to measure the ultraviolet amplitudes. We will measure the optical amplitude with time series photometry. By observing the DBV star GD 358 with the HST, we have a unique opportunity to cross-calibrate the two methods - -- essential if we are to have confidence in the conclusions drawn from either method. The future of asteroseismology of white dwarf stars hinges on these observations; they will not be possible after Feb 97, with the replacement of FOS. ------------------------------------------------------------------------------------ 6727( 10) - 07/19/96 16:14 - [ 2] Observations Description ------------------------ We will use the FOS with the blue Digicon and the G160L grating in RAPID readout mode and the 1 arcsec upper aperture to obtain time resolved spectrophotometry with a sampling interval of 10 sec over the spectral region 1150 Angstrom to 2510 Angstrom. We will observe GD358 for 7 consecutive orbits of HST, which allows the accuracy we need to differentiate between A_1400A/A_5500A = 2.1 for l=1 and A_1400A/A_5500A = 2.5 for l=2. Further, we will be able to distinguish between l=1and l=2 geometries in the large amplitude LCFs at the 3-4 Sigma level. The centering will be done with a 4 stage peak-up procedure ensuring 0.04 arcsec centering accuracy on the target, necessary for S/N> 30. We have chosen the G160L grating because we wish to measure the amplitude of pulsation at shortest wavelength possible, were the dependence on l is strong, but also the widest coverage possible because the changes we will measure are continuum variations. The same setup was used on proposals G0-5581 and G0-6011, with success. The beat periods between the pulsations we will study are 2-4 hours, and hence will be well sampled in the 7 orbits. Note since the central (m=0) components strongly dominate each multiplet, we need not resolve the fine structure with the HST observations. Real Time Justification ----------------------- We will observe GD358 with photoelectric photometry at McDonald Observatory contemporaneously with the HST observations to assure a good measurement of the optical amplitudes. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: , ------------------------------------------------------------------------------------ 6727( 10) - 07/19/96 16:14 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 V777HER STAR,DB, RA=16H 47M 18.64S +/- J2000 V = 13.65 0.3",DEC=32D 28' 32.32" +/- B = 13.54 0.3",PLATE-ID=0380 B-V = -0.11 U-B = -1.04 TYPE=DBV Comments: The coordinates were obtained using the DSS. The proper motion and parallax were obtained from The General Catalogue of Trigonometric Stellar Parallax (1991). Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) B1983.29199 -0.01156 0.038 0.0273 6727( 10) - 07/19/96 16:14 - [ 4] Visit: 01 Visit Requirements: SCHEDULABILITY 40% BETWEEN 12-AUG-1996 AND 20-AUG-1996 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 V777HER FOS/BL ACQ/PEA 4.3 G270H SCAN-STEP-Y=1.23,SEARCH-SIZE-Y=3, 1 1.0 S ONBOARD ACQ FOR 20 K SEARCH-SIZE-X=1,TYPE=UP Comments: Stage 1 of 4 Stage peakup. ------------------------------------------------------------------------------------------------------------------------------------ 20 V777HER FOS/BL ACQ/PEA 1.0-PAI G270H SCAN-STEP-X=0.61,SCAN-STEP-Y=0.61 1 1.0 S ONBOARD ACQ FOR 30 K R-A ,SEARCH-SIZE-X=6,SEARCH-SIZE-Y=2, TYPE=UP Comments: Stage 2 of 4 Stage peakup. ------------------------------------------------------------------------------------------------------------------------------------ 30 V777HER FOS/BL ACQ/PEA 0.5-PAI G270H SCAN-STEP-X=0.29,SCAN-STEP-Y=0.29 1 1.0 S ONBOARD ACQ FOR 40 K R-A ,SEARCH-SIZE-X=3,SEARCH-SIZE-Y=3, TYPE=UP Comments: Stage 3 of 4 Stage peakup. ------------------------------------------------------------------------------------------------------------------------------------ 40 V777HER FOS/BL ACQ/PEA 0.25-PA G270H SCAN-STEP-X=0.110, 1 2.6 S ONBOARD ACQ FOR 50 K IR-A SCAN-STEP-Y=0.110,sEARCH-SIZE-X=4 ,TYPE=UP,SEARCH-SIZE-Y=4 Comments: Stage 4 (the last Stage) of 4 Stage peakup. Changed to P4 peakuP ------------------------------------------------------------------------------------------------------------------------------------ 50 V777HER FOS/BL RAPID 1.0-PAI G160L STEP-PATT=SINGLE,READ-TIME=10.0, 6 2750 S R-A COMB=YES,SUB-STEP=4 ------------------------------------------------------------------------------------------------------------------------------------ 6727( 10) - 07/19/96 16:14 - [ 5] Summary Form for Proposal 6727 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOS/BL ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/PEAK RAPID ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SCAN-STEP-Y=1.23 SEARCH-SIZE-Y=3 SEARCH-SIZE-X=1 TYPE=UP SEARCH-SIZE-Y=2 SEARCH-SIZE-X=3 SEARCH-SIZE-Y=4 SUB-STEP=4 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category HOT STARS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements SCHEDULABILITY 40% BETWEEN 12-AUG-1996 AND 20-AUG-1996 ONBOARD ACQ FOR 20 ONBOARD ACQ FOR 30 ONBOARD ACQ FOR 40 ONBOARD ACQ FOR 50 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G270H G160L ------------------------------------------------------------------------------------------------------------------------------------ Target Names V777HER ------------------------------------------------------------------------------------------------------------------------------------