Determining the core stratification in white dwarfs with asteroseismology

¹ Université de Toulouse, UPS-OMP, IRAP, Toulouse, F-31400, France
² CNRS, IRAP, 14 avenue Edouard Belin, F-31400 Toulouse, France
³ Département de Physique, Université de Montréal, CP 6128, Succursale Centre-Ville, Montréal, QC H3C 3J7, Canada

^* stephane.charpinet@irap.omp.eu
^** ngiammichele@irap.omp.eu
^*** brassard@astro.umontreal.ca
^**** fontaine@astro.umontreal.ca

Published online: 8 September 2017

Abstract

Using the forward modeling approach and a new parameterization for the core chemical stratification in ZZ Ceti stars, we test several situations typical of the usually limited constraints available, such as small numbers of observed independent modes, to carry out asteroseismology of these stars. We find that, even with a limited number of modes, the core chemical stratification (in particular, the location of the steep chemical transitions expected in the oxygen profile) can be determined quite precisely due to the significant sensitivity of some confined modes to partial reflexion (trapping) effects. These effects are similar to the well known trapping induced by the shallower chemical transitions at the edge of the core and at the bottom of the H-rich envelope. We also find that success to unravel the core structure depends on the information content of the available seismic data. In some cases, it may not be possible to isolate a unique, well-defined seismic solution and the problem remains degenerate. Our results establish that constraining the core chemical stratification in white dwarf stars based solely on asteroseismology is possible, an opportunity that we have started to exploit.