Adiabatic properties of pulsating DA white dwarfs. II - Mode trapping in compositionally stratified models
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Abstract
In order to elucidate the adiabatic gravity-mode period structure of models of pulsating DA white dwarfs, the phenomenon of mode trapping caused by compositional layering in these stars is examined qualitatively and quantitatively. The various manifestations of compositional layering on the pulsational properties of a representative ZZ Ceti star model are discussed. A semianalytic formula relating the periods of trapped modes to model properties, which can readily be used to estimate the hydrogen layer mass in a ZZ Ceti star, is derived. An analytic expression which gives the full period spectrum of the model in terms of only four parameters is found. It is shown that these four parameters are related to the structural properties of a star. A procedure is proposed for analyzing future observations of ZZ Ceti stars in terms of mode trapping.