The white dwarf mass–radius relation and its dependence on the hydrogen envelope.

ROMERO, ALEJANDRA D; LAUFFER, G R; KEPLER, S O; CÓRSICO, A H; JOYCE, S R G

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2019

0035-8711

We present a study of the dependence of the mass-radius relation for DAwhite dwarf stars on the hydrogen envelope mass and the impact on thevalue of log g, and thus the determination of the stellar mass. Weemploy a set of full evolutionary carbon-oxygen core white dwarfsequences with white dwarf mass between 0.493 and 1.05M⊙. Computations of the pre-white-dwarf evolutionuncovers an intrinsic dependence of the maximum mass of the hydrogenenvelope on the stellar mass; i.e. it decreases when the total massincreases. We find that a reduction of the hydrogen envelope mass canlead to a reduction in the radius of the model of up to {? } 12{{per cent}}. This translates directly to an increase in log g for a fixedstellar mass, which can reach up to 0.11 dex, mainly overestimating thedeterminations of stellar mass from atmospheric parameters. Finally, wefind a good agreement between the results from the theoreticalmass-radius relation and observations from white dwarfs in binarysystems. In particular, we find a thin hydrogen mass of MH? 2 × 10-8 M⊙ for 40 Eridani B, inagreement with previous determinations. For Sirius B, the spectroscopicmass is 4.3 per cent lower than the dynamical mass. However, the valuesof mass and radius from gravitational redshift observations arecompatible with the theoretical mass-radius relation for a thickhydrogen envelope of MH = 2 × 10-6M⊙.