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

TL;DR

This paper provides detailed mass-radius relations for white dwarf stars with various core compositions, including recent focus on iron cores suggested by Hipparcos data, using an updated stellar evolutionary code.

Contribution

It presents new, accurate mass-radius relations for white dwarfs with multiple core compositions, especially iron, incorporating effects of diffusion and finite temperature.

Findings

Mass-radius relations vary significantly with core composition.

Iron-core white dwarfs have distinct mass-radius characteristics.

Diffusion effects influence low-mass helium white dwarf models.

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, by using a fully updated stellar evolutionary code. We considered masses from 0.15 to 0.5 Mo for the case of helium core, from 0.45 to 1.2 Mo for carbon, oxygen and silicon cores and from 0.45 to 1.0 Mo for the case of an iron core. In view of 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. Furthermore, we explore the effects of gravitational, chemical and thermal diffusion on low-mass helium WD models with hydrogen and helium envelopes.