On the Effect of Explosive Thermonuclear Burning on the Accreted Envelopes of White Dwarfs in Cataclysmic Variables

TL;DR

This paper investigates how explosive thermonuclear burning influences the composition of white dwarf envelopes in cataclysmic variables, highlighting contamination from nova ejecta as a key factor.

Contribution

It presents evidence that some CVs' donor stars are contaminated by nova ejecta, affecting the white dwarf's accreted envelope composition, a novel insight into CV evolution.

Findings

Heavy elements in white dwarf atmospheres suggest explosive burning.

Donor stars may be contaminated by nova ejecta.

Contamination impacts the understanding of CV progenitors.

Abstract

The detection of heavy elements at suprasolar abundances in the atmospheres of some accreting white dwarfs in cataclysmic variables, coupled with the high temperatures needed to produce these elements requires explosive thermonuclear burning. The central temperatures of any formerly more massive secondary stars in CVs undergoing hydrostatic CNO burning are far too low to produce these elements. Evidence is presented that at least some cataclysmic variables contain donor secondaries that have been contaminated by repeated novae ejecta and are transferring this material back to the white dwarf. This scenario does not exclude the channel in which formerly more massive donor stars underwent CNO processing in ystems that underwent thermal timescale mass transfer. Implications for the progenitors of CVs are discussed.