Old White Dwarf Stars with Some Hydrogen -- Cooling Curves

TL;DR

This paper provides a detailed theoretical analysis of old white dwarf stars with varying small amounts of surface hydrogen, focusing on their convective mixing and cooling evolution.

Contribution

It offers the first self-consistent, quantitative models of convective mixing and cooling curves for white dwarfs with small hydrogen layers.

Findings

Numerical cooling and chemical evolution curves are derived.

Convective mixing significantly affects white dwarf evolution.

Results will aid in understanding the non-DA gap in white dwarf populations.

Abstract

We present theoretical analysis on old white dwarf stars with \emph{some} hydrogen, that possess a mass of surface hydrogen from $1\times10^{-11}M_{\sun}$ to $1\times10^{-7}M_{\sun}$. The evolution of such objects is complicated by convective mixing from surface convection zone to the underlying helium layer. In this paper, we provide first self-consistent, quantitative investigation on the subject of convective mixing. Numerical cooling curves and chemical evolution curves are obtained as a function of white dwarf mass and hydrogen content. Such results will be applied to the investigation of the non-DA gap of \citet{1997ApJS..108..339B} in a later paper.