The ZZ Ceti Instability Strip: Facts and Fallacies

Abstract

Bergeron et al. (1995); (B95 hereafter) have combined optical spectroscopy with ultraviolet observations to produce the most comprehensive analysis of the atmospheric properties of ZZ Ceti stars. In that study, it was shown that model atmospheres calculated with the so-called ML2/α = 0.6 version of the mixing-length theory provides the best internal consistency between optical and UV effective temperatures, trigonometric parallaxes, V magnitudes, and gravitational redshifts. With this internal consistency achieved, it is then possible to rely on high signal-to-noise optical spectroscopy alone to determine with great accuracy the atmospheric parameters (T _eff and log g) of any ZZ Ceti star. However, this optimistic view has been criticized repeatedly (see Koester & Holberg 2001 and references therein). Here we review and dismiss some of the arguments presented in these papers.