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.
Massive pulsating white dwarf stars are extremely rare, because they are the final product of intermediate-mass stars, which are less common than low-mass stars. Additionally, their small size makes them fainter than the normal-mass white dwarf stars (∼0.6 M ⊙). Our motivation to look for this type of variable is to be able to study in detail their internal structure and therefore derive properties for the outcome of the evolution of intermediate mass stars, below 10 M ⊙. Using the 2.1 m Otto Struve Telescope at McDonald Observatory, we report on the discovery of a new massive pulsating white dwarf star. These stars might be massive enough that their cores have a significant crystallized portion, up to about 50%. A detailed asteroseismic study of these stars will provide important constrains on intermediate-mass stellar evolution, and the opportunity to study solid state physics at extreme conditions.
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