Light variability of white dwarfs and subdwarfs due to surface abundance spots

TL;DR

This paper models how surface abundance spots on white dwarfs and subdwarfs, caused by elemental diffusion or debris accretion, can lead to observable light variability, similar to that seen in chemically peculiar stars.

Contribution

It introduces a model for light variability in white dwarfs and subdwarfs caused by surface abundance spots, expanding understanding beyond main-sequence stars.

Findings

Iron overabundance spots can cause observable variability in hot white dwarfs.

Debris accretion may induce detectable light changes in warm white dwarfs.

The model explains most light variations observed in the star HD 144941.

Abstract

Classical main-sequence chemically peculiar stars show light variability that originates in surface abundance spots. In the spots, the flux redistribution due to line (bound-bound) and bound-free transitions is modulated by stellar rotation and leads to light variability. White dwarfs and hot subdwarfs may also have surface abundance spots either owing to the elemental diffusion or as a result of accretion of debris. We model the light variability of typical white dwarfs and hot subdwarfs that results from putative surface abundance spots. We show that the spots with radiatively supported iron overabundance may cause observable light variability of hot white dwarfs and subdwarfs. Accretion of debris material may lead to detectable light variability in warm white dwarfs. We apply our model to the helium star HD 144941 and conclude that the spot model is able to explain most of observed light variations of this star.