THEORETICAL-MODELS FOR ASTEROSEISMOLOGY OF DA WHITE-DWARF STARS

Because white dwarfs are the most common end state of stellar evolutio n, determining their internal structure will yield many clues about th e final stages of stellar evolution and the physics of matter under ex treme conditions. We present the results of our parametric survey of e volutionary models of compositionally stratified white dwarfs with hyd rogen surface layers (DA white dwarfs) and provide a comprehensive set of theoretical g-mode pulsation periods for comparison to observation s of pulsating DA white dwarfs. This survey complements the previous s urvey of helium atmosphere (DB) white dwarf periods of Bradley, Winget , & Wood. We show how to use the periods of low-overtone and/or trappe d modes to constrain the internal structure of pulsating DA white dwar fs by utilizing their sensitivity to the total stellar mass and the lo cation of the hydrogen/helium transition zone. We use G117-B15A as an example to demonstrate the potential of our models for asteroseismolog y; we suggest that G117-B15A has a mass of 0.55 M. and a hydrogen laye r mass of approximate to 1.5 x 10(-4) M.