Constraining the Surface Inhomogeneity and Settling Times of Metals on Accreting White Dwarfs

TL;DR

This paper explores how pulsation-induced temperature variations and time-variable accretion influence metal distribution and settling times on white dwarf surfaces, providing new diagnostic tools and constraints based on observational data.

Contribution

It introduces a method to diagnose surface metal inhomogeneity and settling times in white dwarfs using pulsation effects and accretion variability.

Findings

Temperature variations cause observable metal distribution signatures.

Time-variable accretion affects metal abundances and settling time estimates.

Current data can constrain surface inhomogeneity and settling times.

Abstract

Due to the short settling times of metals in DA white dwarf atmospheres, any white dwarfs with photospheric metals must be actively accreting. It is therefore natural to expect that the metals may not be deposited uniformly on the surface of the star. We present calculations showing how the temperature variations associated with white dwarf pulsations lead to an observable diagnostic of the surface metal distribution, and we show what constraints current data sets are able to provide. We also investigate the effect that time-variable accretion has on the metal abundances of different species, and we show how this can lead to constraints on the gravitational settling times.