! File: 4634C.PROP ! Database: PEPDB ! Date: 22-FEB-1994:20:34:27 coverpage: title_1: THE RED EDGE OF THE ZZ CETI INSTABILITY STRIP:CYCLE3 MEDIUM sci_cat: HOT STARS sci_subcat: WHITE DWARFS proposal_for: GO pi_fname: NICOLE pi_mi: F. pi_lname: ALLARD pi_inst: OBSERVATOIRE DE MEUDON pi_country: FRANCE hours_pri: 1.27 num_pri: 1 fos: Y funds_amount: 19500 funds_length: 12 funds_date: OCT-93 off_fname: HARVILL off_mi: C. off_lname: EATON off_title: VICE-CHANCELLOR off_inst: LOUISIANA STATE UNIVERSITY off_addr_1: OFFICE OF RESEARCH AND ECONOMIC DEVELOPMENT off_addr_2: LOUISIANA STATE UNIVERSITY AND off_addr_3: AGRICULTURAL AND MECHANICAL COLLEGE off_city: BATON ROUGE off_state: LA off_zip: 708034001 off_country: USA ! end of coverpage abstract: line_1: ZZ Ceti stars are variable white dwarfs of spectral type DA. The line_2: theoretically predicted instability strip depends on several line_3: uncertain assumptions, most importantly the efficiency of line_4: convective energy transport and the detailed structure of the line_5: outer stellar layers (chemical stratification, thickness of line_6: hydrogen layers). Empirical determinations are so far not as line_7: accurate as desirable for a comparison, because: (i) the Balmer line_8: lines in the optical region reach maximum strengths within the line_9: instability strip and therefore vary only little with line_10: temperature, and (ii) the use of the ultraviolet spectrum, which line_11: is dominated by the line wing of Lyman alpha with quasimolecular line_12: satellites at 1400 and 1600 A has been hampered by the lack of line_13: an adequate theoretical description of the line shape. This line_14: theory has now been developed by one of us (N.Allard) and line_15: incorporated into stellar atmosphere programs, allowing us to line_16: determine effective temperatures in this range with an accuracy line_17: of 200 K. In Cycle 2 we will obtain observations of the line_18: apparently hottest ZZ Ceti object (G117-B15A). In this project line_19: we want to observe G255-2 - possibly the coolest ZZ Ceti - to line_20: get a good estimate for the red edge of the instability region. ! ! end of abstract general_form_proposers: lname: ALLARD fname: NICOLE title: PI mi: F. inst: OBSERVATOIRE DE MEUDON country: FRANCE esa: Y ! lname: KOESTER fname: DETLEV mi: G. inst: LOUISIANA STATE UNIVERSITY country: USA ! lname: VAUCLAIR fname: GERARD mi: P. inst: OBSERVATOIRE MIDI PYRENEES, TOULOUSE country: FRANCE esa: Y ! ! end of general_form_proposers block general_form_text: question: 2 section: 1 line_1: The ZZ Ceti stars form a class of non-radially pulsating DA white line_2: dwarfs, confined to a narrow instability strip centered around Teff line_3: 12000 K. It is very likely that all DA white dwarfs start to pulsate line_4: when their evolution leads them through this region. The theory of line_5: these oscillations shows that the exact boundaries of the instability line_6: strip contain much information about the structure of the outer layers line_7: of white dwarfs as well as about fundamental physical processes (see line_8: Wesemael et al. 1991, Nato ASI Series C, Vol. 336,p.159 for a recent line_9: discussion). line_10: We want to determine the red edge of the instability strip using line_11: our recent work on the Lyman alpha satellite features for the spectral line_12: analysis. We have chosen the object G255-2, which in most studies line_13: defines the cool edge. line_14: With the observation proposed here we will be able to answer the line_15: important question, whether the cool edge is close to 10000 K line_16: (suggested by G255-2 and BPM30551) or much hotter (>11000). line_17: G255-2 has been studied extensively in the optical region. Fast line_18: photometry data have been obtained by one of us (Vauclair, line_19: unpublished) and the results will be available. ! question: 3 section: 1 line_1: We want to obtain spectral coverage of the range dominated by the line_2: Lyman alpha red wing satellites, i.e. 1300 - 2300 A, for the variable line_3: white dwarf G255-2. With FOS and the G160L grating we will achieve a line_4: S/N of >20 around 1500 A, where a secondary flux maximum between the line_5: 1400 and 1600 A satellites is extremely temperature sensitive. For line_6: lambda > 1650 A the flux rises steeply in the star, and the expected line_7: S/N ranges from 40 to 100. line_8: The range from 1300 to 2300 A can be covered in one exposure with the line_9: G160L grating. The exposure time necessary has been estimated from a line_10: model spectrum calculated for different effective temperatures between line_11: 10000 and 11000 K and log g = 8.0. The fluxes have been scaled using line_12: the observed V magnitude. A 90 min exposure will give a S/N of >20 for line_13: the regions most sensitive to temperature and surface gravity. ! question: 4 section: 1 line_1: Numerous attempts to determine the boundaries of the instability strip line_2: have been performed with optical or IUE data, among others also by one line_3: of the current CO-PI's (Weidemann and Koester 1984, Astron.Astrophys. line_4: 132, 195). A recent summary of these studies is given in Wesemael et line_5: al. 1991 (White Dwarfs, Nato ASI Series C, Vol.336, p.159). line_6: The red edge of the instability strip is unfortunately defined by 4 line_7: different stars in 4 studies, the coolest ones being BPM30551 and line_8: G255-2 around 10000 K (with large uncertainties), while the next line_9: coolest stars do only appear above 11000 K, thus precluding any firm line_10: conclusions from a comparison with observations. line_11: With V = 16.04 G255-2 is too faint to give a useful spectrum with the line_12: IUE satellite. For an accurate temperature determination and possibly line_13: also a determination of the surface gravity (and thus mass) from the line_14: relative strength of the two Lyman alpha satellites (from neutral and line_15: charged perturbers) we will need a S/N of about 30 in the UV. ! question: 7 section: 1 line_1: The data obtained will be reduced using STSDAS installed on the line_2: SPARCstation of the CO-PI (Koester) at Baton Rouge by Allard and line_3: Koester. line_4: The analysis will consist in the fitting of the final observation line_5: result with synthetic spectra calculated by Koester and collaborators. line_6: Methods for calculating white dwarf model atmospheres and synthetic line_7: spectra have been developed by us over the past 15 years and used and line_8: documented in numerous publications. A complete grid of model line_9: atmospheres covering the range of ZZ Ceti stars is available and can line_10: be expanded at any time if necessary. These calculations include the line_11: detailed line profile calculations for Lyman alpha and the line_12: quasimolecular satellites at 1400 and 1600 A obtained recently by line_13: N.Allard, which are essential for the desired accuracy of the line_14: temperature determination of this project. ! question: 9 section: 1 line_1: Data for our project ID3447 were obtained in November 1992. We are line_2: currently trying to understand a factor of two difference in the line_3: absolute fluxes compared to a (very noisy) IUE spectrum, and at the line_4: same time proceeding with the spectral analysis. ! question: 10 section: 1 line_1: The Observatoire de Meudon provides computing facilities and basic line_2: support (secretarial, technical programming etc.) for N. Allard. line_3: The computing facilities of the Department of Physics (Workstations) line_4: and Louisiana State University (Mainframes) will also be available for line_5: this project essentially free of charge. ! !end of general form text general_form_address: lname: ALLARD fname: NICOLE mi: F. category: PI inst: Observatoire de Meudon addr_1: OBSERVATOIRE DE MEUDON addr_2: DEPARTEMENT ATOMES ET MOLECULES EN ASTROPHYSIQUE addr_3: F-92195 MEUDON PRINCIPAL CEDEX city: MEUDON country: FRANCE phone: 33-1-45077449 ! ! end of general_form_address records fixed_targets: targnum: 1 name_1: WD1159+803 name_2: G255-2 descr_1: A,177 pos_1: PLATE-ID=01G5, pos_2: RA = 12H01M45.699S +/- 0.3", pos_3: DEC = +80D05'00.47" +/- 0.3" equinox: 2000 pm_or_par: Y pos_epoch_bj: J pos_epoch_yr: 1984.20 ra_pm_val: -0.087875 dec_pm_val: -0.0400 fluxnum_1: 1 fluxval_1: V = 16.04 +/- 0.05 fluxnum_2: 2 fluxval_2: F-CONT(1700) = 4.00 +/- 0.5 E-15 fluxnum_3: 3 fluxval_3: F-CONT(1660) = 1.41 +/- 0.2 E-14 ! ! end of fixed targets ! No solar system records found ! No generic target records found exposure_logsheet: linenum: 1.000 targname: WD1159+803 config: FOS/BL opmode: ACQ/BINARY aperture: 4.3 sp_element: MIRROR num_exp: 1 time_per_exp: 13.0S fluxnum_1: 1 priority: 1 param_1: NTHSTAR=1 req_1: CYCLE 3 / 1.00-3.00; req_2: ONBOARD ACQ FOR 2.00; ! linenum: 2.000 targname: WD1159+803 config: FOS/BL opmode: ACQ/PEAK aperture: 0.25X2.0 sp_element: MIRROR num_exp: 1 time_per_exp: 13.0S fluxnum_1: 1 priority: 1 param_1: TYPE=UP req_1: ONBOARD ACQ FOR 3.00; req_2: SPATIAL SCAN; ! linenum: 3.000 targname: WD1159+803 config: FOS/BL opmode: ACCUM aperture: 0.25X2.0 sp_element: G160L wavelength: 1600 num_exp: 1 time_per_exp: 76.0M fluxnum_1: 2 priority: 1 ! ! end of exposure logsheet scan_data: line_list: 2.00 fgs_scan: cont_dwell: D dwell_pnts: 7 dwell_secs: 1.00 scan_width: 0.0000 scan_length: 0.3000 sides_angle: 90.0000 number_lines: 1 scan_rate: 0.0000 first_line_pa: 90.0000 scan_frame: S/C len_offset: 0.150 wid_offset: 0.0 ! ! end of scan data