The ZZ Ceti Stars and the Rate of Evolution of White Dwarfs

Abstract

The importance of the ZZ Ceti stars, and indeed the importance of all pulsating stars, derives from the fact that stellar pulsations probe the interiors of stars, and thus they test directly our models of stellar interiors and stellar evolution. The relative value of stellar pulsations as such a probe depends on, among other factors, the number of pulsation modes simultaneously excited in a star, as each additional mode depends on and constrains the properties of the star in a different way. Judged by this criterion, the pulsations of the ZZ Ceti stars should be unusually valuable because all ZZ Ceti stars are multi-mode variables. For example, among the ZZ Ceti stars with well studied light curves, the one with the fewest modes is R548 (= ZZ Ceti itself) with 4 pulsation modes simultaneously excited (Robinson et al. 1976), while some of the other ZZ Ceti stars can have dozens of pulsation modes simutaneously excited (cf. Robinson 1979).