Understanding the Cool DA White Dwarf Pulsator, G29−38

The white dwarfs are promising laboratories for the study of cosmochronology\nand stellar evolution. Through observations of the pulsating white dwarfs, we can\nmeasure their internal structures and compositions, critical to understanding post main\nsequence evolution, along with their cooling rates, allowing us to calibrate their ages\ndirectly. The most important set of white dwarf variables to measure are the oldest\nof the pulsators, the cool DAVs, which have not previously been explored through\nasteroseismology due to their complexity and instability. Through a time-series\nphotometry data set spanning ten years, we explore the pulsation spectrum of the\ncool DAV, G29–38 and find an underlying structure of 19 (not including multiplet\ncomponents) normal-mode, probably ℓ = 1 pulsations amidst an abundance of time\nvariability and linear combination modes. Modelling results are incomplete, but\nwe suggest possible starting directions and discuss probable values for the stellar\nmass and hydrogen layer size. For the first time, we have made sense out of the\ncomplicated power spectra of a large-amplitude DA pulsator. We have shown its\nseemingly erratic set of observed frequencies can be understood in terms of a recurring\nset of normal-mode pulsations and their linear combinations. With this result, we\nhave opened the interior secrets of the DAVs to future asteroseismological modelling,\nthereby joining the rest of the known white dwarf pulsators.