August 11-15, 2014


Determination of the Core Composition of ZZ Ceti Stars through Seismic Means

Noemi Giammichele (Université de Montréal)

G. Fontaine (U. de Montréal), S. Charpinet (IRAP/OMP/Toulouse), & P. Brassard (U. de Montréal)

The pulsation periods detected in ZZ Ceti pulsators are mostly sensitive to the surface gravity (total mass), effective temperature, and envelope layering, particularly the thickness of the outermost hydrogen envelope. There is also some sensitivity of the pulsation periods on the core composition, but this is more difficult to exploit and must usually rely on the detection of modes that have larger amplitudes in the core, i.e., modes that are confined below the envelope. Unfortunately, the exact details of the C/O composition profile in the core are still very much uncertain as demonstrated by comparing the results obtained by various investigators: Falk Herwig, Maurizio Salaris, the La Plata Group, and results obtained with the recently-available MESA code. In brief, for comparable masses, significant differences exist in the final post-AGB core chemical profile. Moreover, these profiles suffer from numerical noise which is the consequence of the accumulated uncertainties associated with the way the various codes handle the technical difficulties of pre-white dwarf evolution. This numerical noise is a real "killer" in asteroseismological exercises. Until significant progress is made on that front, we believe that only the bulk composition of the core, as opposed to its detailed chemical profile, can be inferred with some confidence. We show that the bulk composition of Ross 548 can be effectively determined, while that of GD 165 is not easily pinned down due to the lack of detected confined modes in that latter case.

Mode of presentation: poster