Mass-radius relations for white dwarf stars of different internal compositions

Abstract

The purpose of this work is to present accurate and detailed mass-radius relations for white dwarf (WD) models with helium, carbon, oxygen, silicon and iron cores, and with and without a hydrogen envelope, by using a fully updated stellar evolutionary code. We considered masses from 0.15 M_sun to 0.5 M_sun for the case of helium core, from 0.45 M_sun to 1.2 M_sun for carbon, oxygen and silicon cores, and from 0.45 M_sun to 1.0 M_sun for the case of an iron core. In view of the recent measurements made by Hipparcos that strongly suggest the existence of WDs with an iron-dominated core, we focus our attention mainly on the finite-temperature, mass-radius relations for WD models with iron interiors. In addition, we explore the effects of gravitational, chemical and thermal diffusion on low mass helium white dwarf models with hydrogen and helium envelopes.