Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 3798c Report Date: 09-May-96:18:50 Version: ********** Check-in Date: ********** 1.Proposal Title: A SEARCH FOR RADIAL PULSATIONS IN WHITE DWARFS ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID STELLAR ASTROPHYSICS GO Sub Category PULSATING STARS ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Steven D. Kawaler IOWA STATE UNIVERSITY USA 515-294-9728 ------------------------------------------------------------------------------------ 7. Abstract Several classes of NONRADIALLY pulsating white dwarfs are known, with pulsation periods of several minutes. Theoretical work predicts that DB and DA white dwarfs that are slightly hotter than the known nonradial instability strips should be unstable to RADIAL pulsations with periods of about 0.1--1 second. However, ground- based observations have failed to reveal such periodicities. We propose to use HST's High Speed Photometer to search for the predicted radial pulsations in DB and DA white dwarfs. UV high-speed photometry offers the advantages of larger stellar fluxes (the effective temperatures of our three targets are 13,000--30,000 K) and significantly larger pulsation amplitudes (factors of 2 to 3) compared to ground- based photometry, along with freedom from atmospheric scintillation, giving HST a distinct gain over any ground-based facility. The presence (or absence) of the predicted rapid oscillations will provide significant new information for (or challenges to) the theory of white-dwarf pulsations, structure, and evolution. ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 1.50 par: 0 10. Num targs pri: 3 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: HSP ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 3798c PI: Steven D. Kawaler Proposal Title: A SEARCH FOR RADIAL PULSATIONS IN WHITE DWARFS ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Pi Steven D. Kawaler IOWA STATE UNIVERSITY USA Howard E. Bond SPACE TELESCOPE SCIENCE USA INSTITUTE ------------------------------------------------------------------------------------ 2. Scientific Justification. Scientific Justification. ------------------------------------------------------------------------------------ 3. Description of proposed observations. Short Description of Observations. We will obtain high-speed photometry of white dwarfs with the HSP. Since the predicted periods lie in the range 0.1-10 sec, we will use a time resolution of 0.01 sec. The observing runs on each target will be 30 min long. To maximize the count rates, we will use the F140LP filter with the largest available aperture (the 10" acquisition aperture). ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. Justify need for HST. The principal advantages of performing this investigation with HST arise from its UV capabilities and the lack of scintillation noise in observations from space. For integration times of 0.05 second, r.m.s. intensity fluctuations from scintillation are about 1 percent in a 4-m telescope. The lack of scintillation noise with ST therefore pushes the amplitude limit well below that available to ground-based instruments. The two primary candidate targets are white dwarfs that are much brighter in UV than in optical wavelengths. In the F140LP configuration a 25,000K blackbody radiates roughly 60 times more energy per second than in the V band, and 6.5 times more than between 4000 to 7000 A. In addition, for radial pulsations the amplitude of variation in luminosity for a given temperature perturbation scales with the frequency. Therefore, variations in the optical flux of 0.0005 mag correspond to UV variations of 0.001 mag. Over the same total run length upper limits in the UV amplitude correspond to limits 2 times smaller than achieved by Robinson (1984) in the optical. Thus HST is the best instrument to search for radial pulsations in DB (and DA) white dwarfs. No searches for radial pulsations in DB white dwarfs have been made. Optical searches for radial pulsations in DA white dwarfs are summarized by Robinson (1984). An optical 4-m telescope cannot reach the same amplitude limit as HST can in the UV. ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. Justification for realtime data or special scheduling. (none) ------------------------------------------------------------------------------------ 6. Description of special calibration exposures. Justify special calibrations, use of dark time, or ininterrupted exposures. Since we will be looking for low-amplitude multiperiodic signals in the data, we require uninterrupted 30 minute exposures with short integration times. Any interruptions in the data will introduce complex alias structure that would severely hamper our ability to detect the expected weak signals. Page 3 ------------------------------------------------------------------------------------ 7. Data reduction and analysis plans. Plans for data reduction. Analysis of the time-series data will consist of Fourier analysis and power spectrum analysis in a search for power at the relevant frequencies. In the best case, the data from the HSP would be transformed directly. However, the pointing jitter coupled with the expanded PSF introduce excess power at frequencies below 0.6 Hz and complicate any search for longer period modes. While Nelson et al. (1991) show that the system is capable of millimagnitude precision at higher frequencies, we still will need to attempt to compensate for the jitter using knowledge of the PSF and the detailed pointing history available in the engineering data stream. We will then use the measured frequencies in a detailed comparison with theoretical models. This effort will involve computation of a grid of models with the parameters relevant to the observed stars, and computation of the periods and growth rates. ------------------------------------------------------------------------------------ 8. Additional comments or special requests. Additional comments. (none) ------------------------------------------------------------------------------------ 9. Description of previous HST work. Have you received previous HST observing time? Co-I Bond is PI for program 2570 ("Recent Mass Ejection from Planetary-Nebula Nuclei") and is a Co-I for program 2593 ("White Dwarfs"). A portion of the data for program 2570 was obtained on August 6, 1991, just before the Phase 1 proposal was written. ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). Resources to be supplied by your institutions. The home institutions of the P.I. and Co. I. will provide computing facilities, administrative support, and secretarial assistance in support of this investigation. ------------------------------------------------------------------------------------ 11. Address Information Name: STEVEN D. KAWALER Category: PI Institution: IOWA STATE UNIVERSITY Address: DEPARTMENT OF PHYSICS AND ASTRONOMY IOWA STATE UNIVERSITY City: AMES State: IA Zip Code: 50011 Country: USA Telephone: 515-294-9728 Telex (or e-mail): ------------------------------------------------------------------------------------ TARGET LIST a) Fixed Targets ID = 3798c [ 4] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial |Acqui|FLX| Flux data No | Name | Description | Position |Eqnx | Vel. |Prblm|REF| | | | | | | | | ------------------------------------------------------------------------------------------------------------------------------------ 1 PG0112+104 A,119 RA = 01H 14M 37.68S +/- J2000 1 V=15.4 GR409 0.33", 1 TYPE=DB2 DEC = +10D 41' 5.31" +/- 2 B-V=-0.40 0.33", PLATE-ID=00GR Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) B 1982.80 -0.0024 +/- 0.0000 -0.0420 +/- 0.0000 0.0000 +/- 0.0000 ------------------------------------------------------------------------------------------------------------------------------------ 2 GD358 EG239 A,119,175 RA = 16H 47M 18.64S +/- J2000 1 V=13.65 GSC2582-23 0.33", 1 TYPE=DB2 DEC = 32D 28' 32.5" +/- 2 B-V=-0.11 0.33", 2 U-B=-1.04 PLATE-ID=0380 Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) B 1983.29 -0.0131 +/- 0.0000 0.0290 +/- 0.0000 0.0000 +/- 0.0000 ------------------------------------------------------------------------------------------------------------------------------------ 3 G130-5 A,120 RA = 23H 43M 51.09S +/- J2000 1 V=12.92 GSC2771-733 0.33", 1 TYPE=DA4 DEC = +32D 32' 48.2" +/- 2 B-V=0.14 0.33", 2 U-B=-0.61 PLATE-ID=01H1 Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) B 1982.80 -0.0160 +/- 0.0000 -0.0600 +/- 0.0000 0.0000 +/- 0.0000 ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 3798c [ 5] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 | 11 | 12 |13 |14| 15 ------------------------------------------------------------------------------------------------------------------------------------ Line | Seq | Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | S/N |Flx|Pr| Special Number | Name | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| |Rel. Time|Ref| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 PG0112+104 HSP/ ACQ DATA- 1 2.0M 12 1 1 ONBOARD ACQ FOR 2 UV2 FORMAT=WORD PCS MODE F CYCLE 2 ------------------------------------------------------------------------------------------------------------------------------------ 2 PG0112+104 HSP/ SINGLE 10.0 F140LP SAMPLE- 1 30M 1 1 PCS MODE F UV2 TIME=0.01 NON-INT PRECISION=HIGH CYCLE 2 Comments: OBSERVATION IS VERY SENSITIVE TO JITTER; SHOULD BE SCHEDULED TO AVOID DAY-NIGHT TRANSITIONS IF POSSIBLE; OR TRANSITIONS SHOULD BE AT BEGINNING OR END OF EXPOSURE. ------------------------------------------------------------------------------------------------------------------------------------ 2.5 DARK S/C DATA NONE FORMAT=FN 1 1S 1 PAR WITH 2 CRIT OBS CYCLE 2 Comments: THE FN FORMAT IS SPECIFIED IN ORDER TO ASSURE THAT THE ENGINEERING DATA ARE RECORDED AT 32 KBPS, FOR SUBSEQUENT ATTEMPTS TO REMOVE GUIDING JITTER FROM THE HSP PHOTOMETRY ------------------------------------------------------------------------------------------------------------------------------------ 3 GD358 HSP/ ACQ DATA- 1 0.5M 14 1 1 ONBOARD ACQ FOR 4 UV2 FORMAT=WORD PCS MODE F CYCLE 2 ------------------------------------------------------------------------------------------------------------------------------------ 4 GD358 HSP/ SINGLE 10.0 F140LP SAMPLE- 1 30M 1 1 PCS MODE F UV2 TIME=0.01 NON-INT PRECISION=HIGH CYCLE 2 Comments: OBSERVATION IS VERY SENSITIVE TO JITTER; SHOULD BE SCHEDULED TO AVOID DAY-NIGHT TRANSITIONS IF POSSIBLE; OR TRANSITIONS SHOULD BE AT BEGINNING OR END OF EXPOSURE. ------------------------------------------------------------------------------------------------------------------------------------ 4.5 DARK S/C DATA NONE FORMAT=FN 1 1S 1 PAR WITH 4 CRIT OBS CYCLE 2 Comments: THE FN FORMAT IS SPECIFIED IN ORDER TO ASSURE THAT THE ENGINEERING DATA ARE RECORDED AT 32 KBPS, FOR SUBSEQUENT ATTEMPTS TO REMOVE GUIDING JITTER FROM THE HSP PHOTOMETRY ------------------------------------------------------------------------------------------------------------------------------------ 5 G130-5 HSP/ ACQ DATA- 1 1.0M 20 1 1 ONBOARD ACQ FOR 6 UV2 FORMAT=WORD PCS MODE F CYCLE 2 ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 3798c [ 6] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 | 11 | 12 |13 |14| 15 ------------------------------------------------------------------------------------------------------------------------------------ Line | Seq | Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | S/N |Flx|Pr| Special Number | Name | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| |Rel. Time|Ref| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 6 G130-5 HSP/ SINGLE 10.0 F140LP SAMPLE- 1 30M 1 1 PCS MODE F UV2 TIME=0.01 NON-INT PRECISION=HIGH CYCLE 2 Comments: OBSERVATION IS VERY SENSITIVE TO JITTER; SHOULD BE SCHEDULED TO AVOID DAY-NIGHT TRANSITIONS IF POSSIBLE; OR TRANSITIONS SHOULD BE AT BEGINNING OR END OF EXPOSURE. ------------------------------------------------------------------------------------------------------------------------------------ 6.5 DARK S/C DATA NONE FORMAT=FN 1 1S 1 PAR WITH 6 CRIT OBS CYCLE 2 Comments: THE FN FORMAT IS SPECIFIED IN ORDER TO ASSURE THAT THE ENGINEERING DATA ARE RECORDED AT 32 KBPS, FOR SUBSEQUENT ATTEMPTS TO REMOVE GUIDING JITTER FROM THE HSP PHOTOMETRY ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 3798c [ 7] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HSP/UV2 S/C ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ SINGLE DATA ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters DATA-FORMAT=WORD SAMPLE-TIME=0.01 PRECISION=HIGH FORMAT=FN ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 1.50 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category STELLAR ASTROPHYSICS ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category PULSATING STARS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 2; PCS MODE F; CYCLE 2 NON-INT; PAR WITH 2; CRIT OBS; ONBOARD ACQ FOR 4; PAR WITH 4; ONBOARD ACQ FOR 6; PAR WITH 6; ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F140LP ------------------------------------------------------------------------------------------------------------------------------------ Target Names PG0112+104 GR409 GD358 EG239 GSC2582-23 G130-5 GSC2771-733 ------------------------------------------------------------------------------------------------------------------------------------