Proposal_Information ! Section 4 Title: THE ZZ CETI INSTABILITY STRIP AND STELLAR CONVECTION Proposal_Category: GO Scientific_Category: Hot Stars Cycle: 5 Investigators PI_name: Detlev Koester PI_Institution: Universitaet Kiel, Kiel CoI_Name: Nicole Allard CoI_Institution: Observatoire de Paris-Meudon, Meudon Contact: N ! Y or N (designate at most one contact) CoI_Name: Gerard Vauclair CoI_Institution: Observatoire Midi-Pyrenees, Toulouse Contact: N ! Y or N (designate at most one contact) Abstract: ! Free format text (please update) 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. 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. The analysis of G117-B15A (in several studies defining the hot edge of the instability strip), which was observed by us in Cycle 2 confirms that an accuracy of 200 K or better can be achieved. It also shows that convection must be more efficient than normally assumed, and that the temperature of G117-B15A is 1000 K lower than determined previously, raising the question that perhaps GD165, the last remaining hot edge candidate with relatively uncertain temperature determination, defines the blue edge. Questions ! Free format text (please update) Observing_Description: We want to obtain spectral coverage (time averaged) of the range dominated by the Lyman Alpha red wing satellites, i.e. 1250 - 2500 Angstrom, for the variable white dwarf GD165. With FOS/BL and the G160L grating we will achieve a S/N ranging from 30 around 1400 Angstrom\ (H^+ satellite) to 60 at 1600 Angstrom\ (H satellite), and close to 100 in the continuum longward of the satellites in a single orbit. This project would a few years ago have been marginally feasible with IUE. However, our experience on two occasions in 1993 with combined ESA/NASA shifts has convinced us, that in the present state of the IUE satellite it is not possible. A major reason is that we do not simply want to determine effective temperatures from models with well established input physics, but also determine the effect of different assumptions about convection theory through a detailed study of the line profile between 1250 and 1800 Angstrom. For that we need a good signal to noise ratio, especially in the wing of Lyman Alpha, which cannot at present be obtained with IUE. Real_Time_Justification: Calibration_Justification: ! Move appropriate text from Real_Time_Justification Additional_Comments: Fixed_Targets ! Section 5.1 Target_Number: 1 Target_Name: WD1422+095 Alternate_Names: GD165 Description: STAR, ZZ CETI STAR Position: RA=14H 24M 39.42S +/- 0.3", DEC=09D 17' 17.4" +/- 0.3", PLATE-ID=03QS Equinox: 2000 RA_PM: -0.01475 ! Units are seconds of time per year Dec_PM: -0.126 ! Units are seconds of arc per year Epoch: 1982.3 Annual_Parallax: 0.0 Flux: F-CONT(1700) = 6 +/-2 E-14, V=14.32+/-0.2, B-V=0.14+/-0.1 ! Visits ! Section 6 Visit_Number: 1 Exposure_Number: 1 ! Section 6.5 Target_Name: WD1422+095 Config: FOS/BL Opmode: ACQ/BINARY Aperture: 4.3 Sp_Element: MIRROR Number_of_Iterations: 1 Time_Per_Exposure: 5S Special_Requirements: ONBOARD ACQ FOR 2 Exposure_Number: 2 ! Section 6.5 Target_Name: WD1422+095 Config: FOS/BL Opmode: ACCUM Aperture: 1.0 Sp_Element: G160L Wavelength: 1600 Number_of_Iterations: 1 Time_Per_Exposure: 21.5M Visit_Number: 2 Exposure_Number: 1 ! Section 6.5 Target_Name: WD1422+095 Config: FOS/BL Opmode: ACQ/BINARY Aperture: 4.3 Sp_Element: MIRROR Number_of_Iterations: 1 Time_Per_Exposure: 5S Special_Requirements: ONBOARD ACQ FOR 2 Exposure_Number: 2 ! Section 6.5 Target_Name: WD1422+095 Config: FOS/BL Opmode: ACCUM Aperture: 1.0-PAIR-A Sp_Element: G160L Wavelength: 1600 Number_of_Iterations: 1 Time_Per_Exposure: 21.5M 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