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Abstract: We present the first full evolutionary calculations aimed at exploring theorigin of hot DQ white dwarfs. These calculations consistently cover the wholeevolution from the born-again stage to the white dwarf cooling track. Ourcalculations provide strong support to the diffusive-convective-mixing picturefor the formation of hot DQs. We find that the hot DQ stage is a short-livedstage and that the range of effective temperatures where hot DQ stars are foundcan be accounted for by different masses of residual helium and-or differentinitial stellar masses. In the frame of this scenario, a correlation betweenthe effective temperature and the surface carbon abundance in DQs should beexpected, with the largest carbon abundances expected in the hottest DQs. Fromour calculations, we suggest that most of the hot DQs could be the coolerdescendants of some PG1159 stars characterized by He-rich envelopes markedlysmaller than those predicted by the standard theory of stellar evolution. Atleast for one hot DQ, the high-gravity white dwarf SDSS J142625.70+575218.4, anevolutionary link between this star and the massive PG1159 star H1504+65 isplausible.

Author: L. G. Althaus, E. García-Berro, A. H. Córsico, M. M. Miller Bertolami, A. D. Romero

Source: https://arxiv.org/

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