! Proposal 6442, submission 1 ! PI: S. O. Kepler ! Received Mon Feb 5 15:37:11 EST 1996 ! From: elr@aries.as.utexas.edu ! +====================+ ! | PED OUTPUT PRODUCT | ! +====================+ ! ! /home/aries/elr/Props/STGO6/PG1351/Phase2/6442.prop ! Generated by PREPROCESSOR, version 6.0e ! Date: Fri Feb 2 13:47:30 CST 1996 Proposal_Information Title: First Ultraviolet Asteroseismology of a Pulsating DB White Dwarf Proposal_Category: GO Scientific_Category: HOT STARS Cycle: 6 Investigators PI_Name: S. O. Kepler PI_Institution: Universidade Federal do Rio Grande do Sul CoI_Name: Edward L. Robinson CoI_Institution: University of Texas at Austin Contact: CoI_Name: Detlev Koester CoI_Institution: University of Kiel Contact: Abstract: The use of white dwarfs to test calculations of stellar evolution and to measure the history of star formation in the galaxy depends on accurate knowledge of white dwarf interiors. White dwarf pulsations give the most detailed picture of their interiors, but the picture is correct only if the indices of the pulsation modes have been identified correctly. Standard mode identifications are based on matching observed pulsation periods to periods determined from complex theoretical calculations. These methods are circular, prone to mis- identifications, and do not work for stars with few excited pulsations. Other methods of mode identifications must be used to avoid these problems. The wavelength dependence of pulsation amplitudes at ultraviolet wavelengths gives an unambiguous and model-independent signature of the pulsation index. We propose to measure the ultraviolet amplitudes of the pulsations in the pulsating DB white dwarf PG1351+489 with FOS. We choose this star because (1) There are no model- independent mode identifications for any DB white dwarf; (2) The observations will independently test earlier conclusions that some DB white dwarfs rotate differentially and have low- mass helium surface layers; (3) The observations will help define the temperature scale for DB white dwarfs; (4) PG1346+489 has the simplest light curve of any pulsating DB white dwarf, so we avoid the serious complications caused by beating between modes. Questions Observing_Description: We will use the FOS/BL and the G160L grating in the RAPID readout mode to obtain time-resolved spectrophotometry of PG1351+489 from 1150 Angstroms to 2500 Angstroms. A sampling interval of 10 seconds will resolve all features in the light curve while maintaining a good duty cycle for the FOS. We will use the upper 1 arcsec square aperture to avoid a scratch on the photocathode. We will use a 3-stage peak-up instead of a 4-stage peak-up even though a 3-stage peak-up in the 1 arcsec aperture does not center a point source in the aperture well enough to avoid variable light loss due (presumably) to breathing over the HST orbit. We do this because the flux variations introduced by breathing will compromise the data less than the poor signal to noise ratio caused by spending too much time on target acquisition. We estimate the required on-target integration time thusly: At 4200 Angstroms the fractional semi-amplitude of the 489.5 s pulsation is ~7.0% The pulsation is probably an l = 1 or l = 2 mode. From the calculations shown in Figure 1, we estimate that the amplitude will be 14.7% at 1400 Angstroms if it is an l = 1 mode and 17.5% if it is an l = 2 mode. To distinguish the two modes with certainty (~ 5 Sigma), the semi-amplitude in the ultraviolet must be measured with an accuracy no poorer than 0.5%, which requires an 4 * 10^4 photons per resolution element. From the SYNPHOT program we estimate that FOS/BL and the G160L grating will detect ~0.13 photons/s/Angstrom at 1400 Angstroms from PG1351+489. Because the ultraviolet spectrum of DB white dwarfs are almost featureless, we can reduce the resolution of the data to 48 Angstroms (by coadding diodes in blocks of 7) without significant loss of information. We need 6300 seconds of on-target integration time to accumulate 4 * 10^4 photons per 48 Angstroms resolution element. At a declination of 49 degrees, PG1351+489 is visible 56 minutes per orbit, of which 50 minutes are available after target re-acquisition. From discussions with the experts at STScI, we understand that the 2-stage peakup will require 43 min and will take ~1.0 orbits; and the on-target integration time requires at least 2.1 orbits. Thus we require 4 orbits for the project. Real_Time_Justification: No special requirements. We will observe PG1351+489 with CCD and photoelectric photometers at McDonald Observatory to obtain a contemporaneous measurement of its optical light curve. Calibration_Justification: Additional_Comments: Fixed_Targets Target_Number: 1 Target_Name: EM-UMA Alternate_Names: WD1351+489,PG1351+489 Description: STAR,DB,PULSATING VARIABLE, Position: RA=13H 53M 9.85S +/- 0.020S,DEC=48D 40' 21.2" +/- 0.30",PLATE-ID=008S Equinox: J2000 RV_or_Z: RA_PM: 0.0 Dec_PM: 0.0 Epoch: B1983.1 Annual_Parallax: 0.0 Flux: B = 16.38+/-0.5 TYPE=DB2 Comments: Flux(1500)=1.5 +/- 0.1 E-14 Solar_System_Targets Generic_Targets Scan_Data Visits Visit_Number: 01 Visit_Requirements: On_Hold_Comments: Visit_Comments: Exposure_Number: 10 Target_Name: EM-UMA Config: FOS/BL Opmode: ACQ/BINARY Aperture: 4.3 Sp_Element: MIRROR Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 26.82S Special_Requirements: ONBOARD ACQ FOR 20 Comments: Exposure_Number: 20 Target_Name: EM-UMA Config: FOS/BL Opmode: ACQ/PEAK Aperture: 0.25-PAIR-A Sp_Element: G270H Wavelength: Optional_Parameters: SCAN-STEP-Y=0.11,SCAN-STEP-X=0.11,SEARCH-SIZE-Y=4,SEARCH-SIZE-X=4 Number_of_Iterations: 1 Time_Per_Exposure: 35.5S Special_Requirements: ONBOARD ACQ FOR 25-50 Comments: Exposure_Number: 25 Target_Name: EM-UMA Config: FOS/BL Opmode: RAPID Aperture: 1.0-PAIR-A Sp_Element: G160L Wavelength: Optional_Parameters: READ-TIME=10,SUB-STEP=4,COMB=YES,STEP-PATT=SINGLE Number_of_Iterations: 1 Time_Per_Exposure: 340S Special_Requirements: Comments: Exposure_Number: 30 Target_Name: EM-UMA Config: FOS/BL Opmode: RAPID Aperture: 1.0-PAIR-A Sp_Element: G160L Wavelength: Optional_Parameters: READ-TIME=10,COMB=YES,STEP-PATT=SINGLE,SUB-STEP=4 Number_of_Iterations: 1 Time_Per_Exposure: 2840S Special_Requirements: Comments: Exposure_Number: 40 Target_Name: EM-UMA Config: FOS/BL Opmode: RAPID Aperture: 1.0-PAIR-A Sp_Element: G160L Wavelength: Optional_Parameters: READ-TIME=10,COMB=YES,STEP-PATT=SINGLE,SUB-STEP=4 Number_of_Iterations: 1 Time_Per_Exposure: 2840S Special_Requirements: Comments: Exposure_Number: 50 Target_Name: EM-UMA Config: FOS/BL Opmode: RAPID Aperture: 1.0-PAIR-A Sp_Element: G160L Wavelength: Optional_Parameters: READ-TIME=10,COMB=YES,STEP-PATT=SINGLE,SUB-STEP=4 Number_of_Iterations: 1 Time_Per_Exposure: 2620S Special_Requirements: Comments: Data_Distribution ! Defaults indicated; change if desired Medium: 8MM Blocking_Factor: 10 Ship_To: Edward L. Robinson*Department of Astronomy*University of Texas*Austin, TX 78712-1083 Ship_Via: Recipient_Email: elr@aries.as.utexas.edu ! Let us know what you think of this template and software! ! Please send a list of your likes and dislikes to your Program Coordinator