6011( 0) - 07/18/95 19:19 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6011 Version: ********** Check-in Date: ********** 1.Proposal Title: TIME-RESOLVED SPECTROSCOPY OF THE PULSATING DA WHITE DWARF PY VUL ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Hot Stars GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: J. Christopher Clemens Iowa State University CoI: Edward L. Robinson University of Texas N CoI: R. Edward Nather University of Texas N CoI: S. O. Kepler Universidade Federal de Rio Grande do Sul N ------------------------------------------------------------------------------------ 6. Abstract The pulsations of white dwarf stars reveal information about their interiors not accessible by any other means. We can use this information to test theories of white dwarf formation and evolution, and to improve calculations of their cooling rates, making them better chronometers for measuring the age and star formation history of our galaxy. To extract all the information provided by white dwarf pulsations, it is not enough to measure pulsation periods, we must identify the indices which describe the pulsation modes (k, l, and m). HST photometry acquired in November 1993 allowed the first unambiguous identification of l for a ZZ Ceti star (RY LMi = G117-B15A). The identification was possible because the pulsation amplitudes depend strongly on l at wavelengths shorter than 3000 A. We propose to exploit this dependence to measure the l value of the pulsations modes in the ZZ Ceti star PY Vul (=G185-32). We will use the FOS blue Digicon in RAPID readout mode and the G160L grating to acquire UV spectrophotometry with a sampling interval of 10 seconds. Because the pulsation modes in G185-32 are greater in number and shorter in period than those in G117-B15A, determining their l values will yield a more precise measure of G185-32's surface H layer mass. This precision will allow us to confirm or refute standard models of white dwarf formation. ------------------------------------------------------------------------------------ 6011( 0) - 07/18/95 19:19 - [ 2] Observations Description ------------------------ We will obtain time-resolved spectrophotometry using the FOS with the blue Digicon and the G160L grating. This choice gives us the widest possible spectral coverage at the shortest possible wavelengths. We need the short wavelengths because that is where the amplitude dependence on l is strongest; we want the widest coverage because the changes we will measure are continuum variations. G185-32 has 6 pulsation modes ranging in period from 141.9 to 370.2 seconds. We will use an integration time of 10 seconds--- short enough to resolve the pulsations while maximizing the duty cycle of the instrument. We are particularly interested in the two most closely spaced modes (periods of 141.9 and 148.5 s). The beat cycle we must sample to resolve these is less than an hour, but we will have to observe through several beat cycles to measure the 148.5 s mode with sufficient precision (10%) since its amplitude at optical wavelengths is only 0.06%. The predicted count rate for G185-32 (using figure 1.2.3 of the FOS handbook and scaling from the HST flux standards HZ-4 and LB227) is 19 counts/sec/diode at 1500 Angstroms. The amplitude of the 148.5 s mode at this wavelength will be 10 times as large as that we have measured optically, but we must measure it with an accuracy of 10%. Reducing the noise from photon statistics to this level requires counting 2.4 * 10^6 photons, which would take 37 hours for a single pixel. By co-adding 6 pixels, we reduce this to 6.2 hours, which is the on-target time we have requested. At longer wavelengths, where the amplitude of the pulsation is smaller, we will have to co-add more pixels to maintain the necessary precision. We have modified our original request for 11 orbits in one visit to make scheduling easier. We still require that the two visits be consecutive. Real Time Justification ----------------------- We have been allocated the nights of 29 May - 4 June 1995 on the 82" telescope at Mcdonald Observatory and the nights of 29 June - 2 July on the 36" telescope. These observations are required to measure pulsation amplitudes of the target in the U,B,V, and R bands. The HST observations need not be simultaneous with these, but the closer the better. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6011( 0) - 07/18/95 19:19 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 PY-VUL STAR,ZZ CETI STAR, DA RA=19H 37M 13.16S +/- 0.3", 2000 V=12.98 +/- 0.02 DEC=+27D 43' 18.42" +/- 0.3", TYPE=DA4 PLATE-ID=000J B-V=0.17 +/- 0.02 U-B=-0.56 +/- 0.02 Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) B1983.52 0.03298 0.01835 0.0560 6011( 0) - 07/18/95 19:19 - [ 4] Visit: 01 Visit Requirements: BETWEEN 15-MAY-95 AND 15-OCT-95 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 PY-VUL FOS/BL ACQ/PEA 4.3 G570H SEARCH-SIZE-X=1 1 6S ONBOARD ACQ FOR 2 K SEARCH-SIZE-Y=3 SCAN-STEP- Y=1.23 ------------------------------------------------------------------------------------------------------------------------------------ 2 PY-VUL FOS/BL ACQ/PEA 1.0 G570H SEARCH-SIZE-X=6 1 5S ONBOARD ACQ FOR 3 K SEARCH-SIZE-Y=2 SCAN-STEP-X=.61 SCAN-STEP-Y=.61 ------------------------------------------------------------------------------------------------------------------------------------ 3 PY-VUL FOS/BL ACQ/PEA 0.3 G570H SEARCH-SIZE-X=5 1 5S ONBOARD ACQ FOR 4-12 K SEARCH-SIZE-Y=5 SCAN-STEP-X=.17 SCAN-STEP-Y=.17 ------------------------------------------------------------------------------------------------------------------------------------ 4 PY-VUL FOS/BL RAPID 4.3 G160L READ-TIME=10.0 1 2860S Comments: Exposure time is entire visibility period (after guide star and target acquisition). Total of exposures in 1-12 is amount required for adequate signal-to-noise (see observing description). ------------------------------------------------------------------------------------------------------------------------------------ 5 PY-VUL FOS/BL RAPID 4.3 G160L READ-TIME=10.0 1 2860S ------------------------------------------------------------------------------------------------------------------------------------ 6 PY-VUL FOS/BL RAPID 4.3 G160L READ-TIME=10.0 1 2860S ------------------------------------------------------------------------------------------------------------------------------------ 7 PY-VUL FOS/BL RAPID 4.3 G160L READ-TIME=10.0 1 2860S ------------------------------------------------------------------------------------------------------------------------------------ 8 PY-VUL FOS/BL RAPID 4.3 G160L READ-TIME=10.0 1 2860S ------------------------------------------------------------------------------------------------------------------------------------ 9 PY-VUL FOS/BL RAPID 4.3 G160L READ-TIME=10.0 1 2860S ------------------------------------------------------------------------------------------------------------------------------------ 10 PY-VUL FOS/BL RAPID 4.3 G160L READ-TIME=10.0 1 2860S ------------------------------------------------------------------------------------------------------------------------------------ 11 PY-VUL FOS/BL RAPID 4.3 G160L READ-TIME=10.0 1 2860S ------------------------------------------------------------------------------------------------------------------------------------ 12 PY-VUL FOS/BL RAPID 4.3 G160L READ-TIME=10.0 1 2860S ------------------------------------------------------------------------------------------------------------------------------------ 6011( 0) - 07/18/95 19:19 - [ 5] Summary Form for Proposal 6011 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOS/BL ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/PEAK RAPID ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SEARCH-SIZE-X=1 SEARCH-SIZE-Y=3 SCAN-STEP-Y=1.23 SEARCH-SIZE-X=6 SEARCH-SIZE-Y=2 SCAN-STEP-X=.61 SCAN-STEP-Y=.61 SEARCH-SIZE-X=5 SEARCH-SIZE-Y=5 SCAN-STEP-X=.17 SCAN-STEP-Y=.17 READ-TIME=10.0 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Hot Stars ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 15-MAY-95 AND 15-OCT-95 ONBOARD ACQ FOR 2 ONBOARD ACQ FOR 3 ONBOARD ACQ FOR 4-12 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G570H G160L ------------------------------------------------------------------------------------------------------------------------------------ Target Names PY-VUL ------------------------------------------------------------------------------------------------------------------------------------