THE MODELING OF ENERGY-DISTRIBUTIONS AND LIGHT CURVES OF ZZ CETI STARS .1. BASIC THEORY AND SEMIANALYTIC EXPRESSIONS FOR THE EMERGENT FLUX

We produce the first results of an investigation aimed at understanding the characteristics of both the light curves and the instantaneous spectra obtained through time-resolved observations of ZZ Ceti stars: Our ultimate aim is to constrain mode identification in these pulsating stars. We first provide a theoretical framework for the computation of the emergent flux from these objects. In order to make the detailed numerical results amenable to physical interpretation, we next develop first- and second-order analytic expressions for the expected amplitudes of pulsation in terms of temperature perturbations. Our calculations reproduce the harmonics and cross-frequency terms observed in many light curves of ZZ Ceti stars. These nonlinear effects are readily explainable in terms of the nonlinear response of the emergent flux to changes of the local temperature at the stellar surface. We provide analytic results which should be useful in the analysis of fast photometric observations obtained either in white light, in the UBV system, or in the uvby system.