Ensemble Characteristics of the ZZ Ceti Stars

We present the observed pulsation spectra of all known non-interacting ZZCeti stars (hydrogen atmosphere white dwarf variables; DAVs) and examinechanges in their pulsation properties across the instability strip. We confirmthe well established trend of increasing pulsation period with decreasingeffective temperature across the ZZ Ceti instability strip. We do not find adramatic order of magnitude increase in the number of observed independentmodes in ZZ Ceti stars, traversing from the hot to the cool edge of theinstability strip; we find that the cool DAVs have one more mode on averagecompared to the hot DAVs. We confirm the initial increase in pulsationamplitude at the blue edge, and find strong evidence of a decline in amplitudeprior to the red edge. We present the first observational evidence that ZZ Cetistars lose pulsation energy just before pulsations shut down at the empiricalred edge of the instability strip.Comment: ApJ, in press. (26 pages, 3 figures