Abstract
We report the detection of non-radial g-mode oscillations in seven relatively bright (14.4 < B < 16.5) DA white dwarf stars from time-series photometry collected at the Nordic Optical Telescope (NOT) at Roque de Los Muchachos Observatory, Spain. The candidate variable stars were selected from preparatory photometric observations of objects from the Hamburg Quasar Survey (HQS) and from spectroscopy of stars from the Villanova (WD) catalogue. The selection of ZZ Ceti candidate stars from photometric data proved nearly as successful as the more common spectroscopic selection method. The effective temperatures that we derive from both methods are consistent with a pure ZZ Ceti instability strip.
Highlights
ZZ Ceti stars or variable DA (DAV) stars are white dwarf (WD) stars with a hydrogen atmosphere that show non-radial g-mode oscillations
We report the detection of non-radial g-mode oscillations in seven relatively bright (14.4 < B < 16.5) DA white dwarf stars from time-series photometry collected at the Nordic Optical Telescope (NOT) at Roque de Los Muchachos Observatory, Spain
Based on observations made with the Nordic Optical Telescope, and partially based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, as well as on data obtained at the Paranal Observatory of the European Southern Observatory for programmes 165.H-0588 and 167.D-0407
Summary
ZZ Ceti stars or variable DA (DAV) stars are white dwarf (WD) stars with a hydrogen atmosphere that show non-radial g-mode oscillations These oscillations, with known periods from 71 s (G 185−32, Kepler et al 2000) up to 1466 s (HS 0952+1816, Mukadam et al 2004a), can be detected as multi-periodic luminosity variations with amplitudes of the pulsation modes ranging from a fraction of a percent up to about five percent. HDAV pulsators can be used to detect planetary companions of white dwarfs, because due to the high stability of hDAV oscillations (P 4 × 10−15 s s−1, Kepler et al 2005a), an orbiting planet can be detected from variations of the observed arrival times of the pulses For these reasons, a more substantial number of ZZ Cetis suitable for such projects, i.e. sufficiently bright objects with the right pulsational properties, would be an advantage. The total number of known ZZ Ceti stars, including those presented here, is 105
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