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White dwarf evolutionary sequences for low-metallicity progenitors: The impact of third dredge-up
Althaus, Leandro G.; Camisassa, Maria E; Miller Bertolami, Marcelo M; Corsico, Alejandro H.; García-Berro Montilla, Enrique
Universitat Politècnica de Catalunya. Departament de Física Aplicada; Universitat Politècnica de Catalunya. GAA - Grup d'Astronomia i Astrofísica
Context. White dwarfs are nowadays routinely used as reliable cosmochronometers, allowing several stellar populations to be dated.; Aims. We present new white dwarf evolutionary sequences for low-metallicity progenitors. This is motivated by the recent finding that residual H burning in low-mass white dwarfs resulting from Z = 0.0001 progenitors is the main energy source over a significant part of their evolution.; Methods. White dwarf sequences have been derived from full evolutionary calculations that take the entire history of progenitor stars into account, including the thermally pulsing and the post-asymptotic giant branch (AGB) phases.; Results. We show that for progenitor metallicities in the range 0.00003 less than or similar to Z less than or similar to 0.001, and in the absence of carbon enrichment from the occurrence of a third dredge-up episode, the resulting H envelope of the low-mass white dwarfs is thick enough to make stable H burning the most important energy source even at low luminosities. This has a significant impact on white dwarf cooling times. This result is independent of the adopted mass-loss rate during the thermally-pulsing and post-AGB phases and in the planetary nebulae stage.; Conclusions. We conclude that in the absence of third dredge-up episodes, a significant part of the evolution of low-mass white dwarfs resulting from low-metallicity progenitors is dominated by stable H burning. Our study opens the possibility of using the observed white dwarf luminosity function of low-metallicity globular clusters to constrain the efficiency of third dredge up episodes during the thermally-pulsing AGB phase of low-metallicity progenitors.
Peer Reviewed
Àrees temàtiques de la UPC::Física::Astronomia i astrofísica
White dwarf stars
Starts -- Evolution
stars: evolution
stars: interiors
white dwarfs
Estels nans
Attribution-NonCommercial-NoDerivs 3.0 Spain

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