DQ white-dwarf stars with low C abundance: Possible progenitors

Abstract

The present paper focuses on the evolution of hydrogen-deficient white dwarfs with the aim of exploring the consequences of different initial envelope structures on the carbon abundances expected in helium-rich, carbon-contaminated DQ white dwarfs. In particular, the evolutionary link between the DQs with low detected carbon abundances and the PG1159, extreme horizontal branch, and helium-rich R Coronae Borealis (RCrB) stars is explored. We present full evolutionary calculations that take a self-consistent treatment of element diffusion into account as well as expectations for the outer layer chemical stratification of progenitor stars upon entering the white dwarf regime. We find that PG1159 stars cannot be related to any DQ white dwarfs with low C abundances. Instead, we suggest that the latter could constitute the progeny of the giant, helium-rich RCrB stars.

arXiv comment10 pages, 10 figures. Accepted for publication in Astronomy and Astrophysics

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• Asteroseismic inferences on GW Vir variable stars in the frame of new PG 1159 evolutionary models
• New DQ white dwarfs in the Sloan Digital Sky Survey DR4: confirmation of two sequences
• On the Spectral Evolution of Hot White Dwarf Stars. III. The PG 1159$-$DO$-$DB$-$DQ Evolutionary Channel Revisited
• On the Spectral Evolution of Hot White Dwarf Stars. II. Time-dependent Simulations of Element Transport in Evolving White Dwarfs with STELUM
• Analysis of cool DO-type white dwarfs from the Sloan Digital Sky Survey Data Release 10
• The spectral evolution of white dwarfs: where do we stand?