Ensemble characteristics of the ZZ Ceti stars

Abstract

We present the observed pulsation spectra of all known noninteracting ZZ Ceti stars (hydrogen atmosphere white dwarf variables [DAVs]) and examine changes in their pulsation properties across the instability strip.We confirm the well-established trend of increasing pulsation period with decreasing effective temperature across the ZZ Ceti instability strip. We do not find a dramatic order-of-magnitude increase in the number of observed independent modes in ZZ Ceti stars, traversing from the hot to the cool edge of the instability strip; we find that the cool DAVs have one more mode on average than the hot DAVs. We confirm the initial increase in pulsation amplitude at the blue edge and find strong evidence of a decline in amplitude prior to the red edge.We present the first observational evidence that ZZ Ceti stars lose pulsation energy just before pulsations shut down at the empirical red edge of the instability strip.