Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 5314 Report Date: 18-Jul-95:17:08 Version: ********** Check-in Date: ********** 1.Proposal Title: THE RED EDGE OF THE ZZ CETI INSTABILITY STRIP ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID COOL STARS GO Sub Category PULSATING STARS ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Gerard Vauclair OBSERVATOIRE MIDI PYRENEES FRANCE 33-61-332953 ------------------------------------------------------------------------------------ 7. Abstract ZZ Ceti stars are variable white dwarfs of spectral type DA. The theoretically predicted instability strip depends on several uncertain assumptions, most importantly the efficiency of convective energy transport and the detailed structure of the outer stellar layers. Empirical determinations from optical spectra are not as accurate as desirable, because the Balmer lines reach maximum strengths within the instability strip and vary only little with temperature. The UV spectrum is much better suited since we have recently improved the quantitative description of the quasi-molecular satellite features, that vary strongly with temperature and should ultimately allow an accuracy of 200 K. Observations for G117-B15A (defining the hot edge of the instability strip) have been obtained in Nov. 92. In this project, we propose to observe BPM30551, one of the coolest ZZ Ceti stars. ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 1.00 par: 0 10. Num targs pri: 1 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: FOS ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 5314 PI: Gerard Vauclair Proposal Title: THE RED EDGE OF THE ZZ CETI INSTABILITY STRIP ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ 3. Description of proposed observations. We want to obtain spectral coverage of the range dominated by the Lyman alpha red wing satellites, i.e. 1300 - 2500 A, for the variable white dwarf BPM30551. With FOS and the G160L grating we will achieve a S/N of >15 for BPM30551 around 1500 A, where a secondary flux maximum between the 1400 and 1600 A satellites is extremely temperature sensitive. For lambda > 1650 A the flux rises steeply in the star, and the expected S/N ranges from 30 to 80. We will use the ACCUM mode for this object. ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. Numerous attempts to determine the boundaries of the instability strip have been performed with optical or IUE data, among others also by one of the current CO- PI's (Weidemann and Koester 1984, Astron.Astrophys. 132, 195). A recent summary of these studies is given in Wesemael et al. 1991 (White Dwarfs, Nato ASI Series C, Vol.336, p.159). The red edge of the instability strip is unfortunately defined by 4 different stars in 4 studies, the coolest ones being BPM30551 and G255-2 around 10000 K (with large uncertainties), while the next coolest stars do only appear above 11000 K, thus precluding any firm conclusions from a comparison with observations. With V = 15.3 and a very steeply declining flux shortward of 1650 A BPM30551 is too faint to give a useful spectrum with the IUE satellite. For an accurate temperature determination and possibly also a determination of the surface gravity (and thus mass) from the relative strength of the Lyman alpha satellites we will need an average S/N of about 20 in the UV. ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. ------------------------------------------------------------------------------------ 6. Description of special calibration exposures. ------------------------------------------------------------------------------------ 8. Additional comments or special requests. ------------------------------------------------------------------------------------ 9. Description of previous HST work. The first observations (in the White Dwarf Consortium Project) were obtained in June 1992. D.Koester and N.Allard are currently working on the analysis of spectra for L745-46A, together with N.Feautrier (Meudon). This project is not related to the current proposal. Related to the present project, G117-B15A has been observed and the data are being analyzed. G255-2 might be observed during Cycle 3, but the program received Medium priority. ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). Observatoire Midi-Pyrenees provides computing facilities and basic support for G. Vauclair. The Observatoire de Meudon provides computing facilities and basic support (secretarial, technical programming etc.) for N. Allard. The computing facilities of the Institut fuer Theoretische Physik und Sternwarte (University of Kiel) will also be available for this project free of charge. ------------------------------------------------------------------------------------ 11. Address Information Page 3 Name: GERARD VAUCLAIR Category: PI Institution: 5474 Address: OBSERVATOIRE MIDI PYRENEES LABORATOIRE D'ASTROPHYSIQUE DE TOULOUSE 14, AV. E. BELIN, F-31400 TOULOUSE City: TOULOUSE State: Zip Code: Country: FRANCE Telephone: 33-61-332953 Telex (or e-mail): ------------------------------------------------------------------------------------ Name: Category: CON Institution: Address: City: State: Zip Code: Country: Telephone: Telex (or e-mail): ------------------------------------------------------------------------------------ TARGET LIST a) Fixed Targets ID = 5314 [ 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 WD0104-464 A, RA = 01H06M53.241S +/- 2000 1 V = 15.26 +/- 0.05 BPM30551 120, 0.3", 2 F-CONT(1700) = 8.00 +/- 0.5 E-15 177 DEC = -46D8'55.29" +/- 0.3", PLATE-ID = 04FI Comments: RA_PM_VAL IS IN TIME-SEC/YR AS DEMANDED IN THE HANDBOOK Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) B 1979.70 0.0213 +/- 0.0000 0.0800 +/- 0.0000 0.0000 +/- 0.0000 ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 5314 [ 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 WD0104-464 FOS/BL ACQ/ 4.3 MIRROR NTHSTAR=1 1 10.0S 1 1 CYCLE 4 / 1.0-3.0 BINARY ONBOARD ACQ FOR 2.0 ------------------------------------------------------------------------------------------------------------------------------------ 2 WD0104-464 FOS/BL ACQ/ 0.3 MIRROR TYPE=UP 1 2.0S 1 1 ONBOARD ACQ FOR PEAK SEARCH-SIZE-X=5 3.0 SEARCH-SIZE-Y=5 SCAN-STEP- X=.172 SCAN-STEP- Y=.172 ------------------------------------------------------------------------------------------------------------------------------------ 3 WD0104-464 FOS/BL ACCUM 0.3 G160L 1600 1 38.3M 2 1 ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 5314 [ 6] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOS/BL ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/BINARY ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters NTHSTAR=1 TYPE=UP SEARCH-SIZE-X=5 SEARCH-SIZE-Y=5 SCAN-STEP-X=.172 SCAN-STEP-Y=.172 ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 1.00 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category COOL STARS ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category PULSATING STARS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CYCLE 4 / 1.0-3.0; ONBOARD ACQ FOR 2.0; ONBOARD ACQ FOR 3.0 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G160L ------------------------------------------------------------------------------------------------------------------------------------ Target Names WD0104-464 BPM30551 ------------------------------------------------------------------------------------------------------------------------------------