Proposal_Information Title: TIME-RESOLVED SPECTROSCOPY OF THE PULSATING DA WHITE DWARF PY VUL Proposal_Category: GO Scientific_Category: Hot Stars Cycle: 5 Investigators PI_name: J. Christopher Clemens PI_Institution: Iowa State University CoI_Name: Edward L. Robinson CoI_Institution: University of Texas CoI_Name: R. Edward Nather CoI_Institution: University of Texas CoI_Name: S. O. Kepler CoI_Institution: Universidade Federal de Rio Grande do Sul Abstract: ! Free format text (please update) 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. Questions ! Free format text (please update) Observing_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: ! Move appropriate text from Real_Time_Justification Additional_Comments: Fixed_Targets Target_Number: 1 Target_Name: PY-VUL Alternate_Names: G185-32, WD1935+276 Description: STAR,ZZ CETI STAR, DA Position: RA=19H 37M 13.16S +/- 0.3", DEC=+27D 43' 18.42" +/- 0.3", PLATE-ID=000J Equinox: 2000 RA_PM: 0.03298 ! Units are seconds of time per year Dec_PM: 0.01835 ! Units are seconds of arc per year Epoch: B1983.52 Annual_Parallax: 0.0560 Flux: V=12.98 +/- 0.02, TYPE=DA4, B-V=0.17 +/- 0.02, U-B=-0.56 +/- 0.02 Visits Visit_Number: 1 Visit_Requirements: BETWEEN 15-MAY-95 AND 15-OCT-95 Exposure_Number: 1 Target_Name: PY-VUL Config: FOS/BL Opmode: ACQ/PEAK Aperture: 4.3 Sp_Element: G570H Optional_Parameters: SEARCH-SIZE-X=1 SEARCH-SIZE-Y=3 SCAN-STEP-Y=1.23 Number_of_Iterations: 1 Time_Per_Exposure: 6S Special_Requirements: ONBOARD ACQ FOR 2 Exposure_Number: 2 Target_Name: PY-VUL Config: FOS/BL Opmode: ACQ/PEAK Aperture: 1.0 Sp_Element: G570H Optional_Parameters: SEARCH-SIZE-X=6 SEARCH-SIZE-Y=2 SCAN-STEP-X=.61 SCAN-STEP-Y=.61 Number_of_Iterations: 1 Time_Per_Exposure: 5S Special_Requirements: ONBOARD ACQ FOR 3 Exposure_Number: 3 Target_Name: PY-VUL Config: FOS/BL Opmode: ACQ/PEAK Aperture: 0.3 Sp_Element: G570H Optional_Parameters: SEARCH-SIZE-X=5 SEARCH-SIZE-Y=5 SCAN-STEP-X=.17 SCAN-STEP-Y=.17 Number_of_Iterations: 1 Time_Per_Exposure: 5S Special_Requirements: ONBOARD ACQ FOR 4-12 Exposure_Number: 4 Target_Name: PY-VUL Config: FOS/BL Opmode: RAPID Aperture: 4.3 Sp_Element: G160L Optional_Parameters: READ-TIME=10.0 Number_of_Iterations: 1 Time_Per_Exposure: 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). Exposure_Number: 5 Target_Name: PY-VUL Config: FOS/BL Opmode: RAPID Aperture: 4.3 Sp_Element: G160L Optional_Parameters: READ-TIME=10.0 Number_of_Iterations: 1 Time_Per_Exposure: 2860S Exposure_Number: 6 Target_Name: PY-VUL Config: FOS/BL Opmode: RAPID Aperture: 4.3 Sp_Element: G160L Optional_Parameters: READ-TIME=10.0 Number_of_Iterations: 1 Time_Per_Exposure: 2860S Exposure_Number: 7 Target_Name: PY-VUL Config: FOS/BL Opmode: RAPID Aperture: 4.3 Sp_Element: G160L Optional_Parameters: READ-TIME=10.0 Number_of_Iterations: 1 Time_Per_Exposure: 2860S Exposure_Number: 8 Target_Name: PY-VUL Config: FOS/BL Opmode: RAPID Aperture: 4.3 Sp_Element: G160L Optional_Parameters: READ-TIME=10.0 Number_of_Iterations: 1 Time_Per_Exposure: 2860S Exposure_Number: 9 Target_Name: PY-VUL Config: FOS/BL Opmode: RAPID Aperture: 4.3 Sp_Element: G160L Optional_Parameters: READ-TIME=10.0 Number_of_Iterations: 1 Time_Per_Exposure: 2860S Exposure_Number: 10 Target_Name: PY-VUL Config: FOS/BL Opmode: RAPID Aperture: 4.3 Sp_Element: G160L Optional_Parameters: READ-TIME=10.0 Number_of_Iterations: 1 Time_Per_Exposure: 2860S Exposure_Number: 11 Target_Name: PY-VUL Config: FOS/BL Opmode: RAPID Aperture: 4.3 Sp_Element: G160L Optional_Parameters: READ-TIME=10.0 Number_of_Iterations: 1 Time_Per_Exposure: 2860S Exposure_Number: 12 Target_Name: PY-VUL Config: FOS/BL Opmode: RAPID Aperture: 4.3 Sp_Element: G160L Optional_Parameters: READ-TIME=10.0 Number_of_Iterations: 1 Time_Per_Exposure: 2860S Data_Distribution Medium: 8MM ! 8MM or 6250BPI or 1600BPI Blocking_Factor: 10 ! 10 or 1 Ship_To: PI_Address ! STSCI or PI_Address or Ship_Via: UPS ! UPS (2-day) or OVERNIGHT