Seismological Studies of Pulsating DA White Dwarfs Observed with the Kepler Space Telescope and K2 Campaigns 1–8

Abstract

AllS single stars that are born with masses up to 8.5–10 M ⊙ will end their lives as white dwarf (WD) stars. In this evolutionary stage, WDs enter the cooling sequence, where the stars radiate away their thermal energy and are basically cooling. As these stars cool, they reach temperatures and conditions that cause the stars to pulsate. Using differential photometry to produce light curves, we can determine the observed periods of pulsation from the WD. We used the White Dwarf Evolution Code (WDEC) to calculate a grid of over one million models with various temperature, stellar mass, and mass of helium and hydrogen layers and calculated their theoretical pulsation periods. In this paper, we describe our approach to WD asteroseismology using WDEC models, and we present seismological studies for 29 observed DAVs in the Kepler and K2 data sets, 25 of which have never been analyzed using these observations and 19 of which have never been seismically analyzed in any capacity before. Learning about the internal structure of WDs places important constraints on the WD cooling sequence and our overall understanding of stellar evolution for low-mass stars.