Abstract

White dwarfs in the Kepler field

Sandra Greiss (The University of Warwick)

Boris Gansicke (Warwick), JJ Hermes (Warwick), Danny Steeghs (Warwick), Detlev Koester (Kiel), Noemi Giammichele (Montreal), Gilles Fontaine (Montreal)

As white dwarfs cool, they go through instability strips by exhibiting periodic variations about the mean intensity of their light. Asteroseismology can probe the interiors of white dwarfs and provide an insight on their compositions, rotation period, mass, temperature and luminosity, by studying their pulsations. Despite the fact that the Kepler mission provides the best ever time series photometry with an enormous impact on all areas of stellar variability, its field lacked one class of stars in its list of successful discoveries and studies: white dwarfs. We will present our deep optical photometric survey of the Kepler field in U, g, r, i, as well as H-alpha, down to 21st magnitude: the Kepler-INT Survey (KIS, Greiss et al. 2012). We will emphasize on our search for pulsating white dwarfs in the field by presenting our efficient selection method and results. In fact, we find 43 new white dwarfs in the field. In the first two years of the mission, only two pulsating white dwarfs were found. We discovered an additional six new pulsating white dwarfs and obtained Kepler data for four of them. They have atmospheric parameters which place them within the empirical instability strip. On top of these six new pulsating white dwarfs, we have ~10 candidates which we are currently following up. We will present the high-quality Kepler data for the four ZZ Ceti stars that we identified (Greiss et al. (2014), and Greiss et al. in prep), and present preliminary asteroseismic results. Rotational splitting is also detected in all four stars, indicating spin periods of a few days, which confirms that the majority of white dwarfs are born as very slow rotators.

Mode of presentation: oral