Astro/Particle Seminar

The Purity of the ZZ Ceti Instability Strip: A Never Ending Controversy

Pierre Bergeron
Universite de Montreal

Time
Mon. February 5, 2007     12:30 PM     Stirling 201

Abstract

The ZZ Ceti stars represent a class of variable white dwarfs whose optical spectra are dominated by hydrogen lines (DA stars). They occupy a narrow region in the Teff-log g plane known as the ZZ Ceti instability strip, with an average effective temperature around Teff~11,600 K and a width of roughly 1000 K. A precise determination of the hot and cool boundaries of this instability strip may eventually provide important constraints about the structure of the outer layers of DA white dwarfs. Of utmost importance is to determine whether all white dwarfs within the ZZ Ceti instability strip are pulsators. If the strip is indeed pure, ZZ Ceti stars would necessarily represent a phase through which all DA stars must evolve, and thus the results from asteroseismological studies might provide constraints on the properties not only of known ZZ Ceti stars, but on the whole population of DA stars as well. In the first part of my talk I will briefly review the physics of white dwarf atmospheres, with a particular emphasis on ZZ Ceti stars. I will then discuss various techniques for measuring the atmospheric parameters of white dwarfs, and I will also show how these techniques can be applied to constrain the atmospheric convective efficiency. The last part of the talk will be devoted to a critical review of the ongoing controversy regarding the purity of the ZZ Ceti instability strip.

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