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Paper: Determination of the Core Composition of White Dwarfs in M67
Volume: 493, 19th European Workshop on White Dwarfs
Page: 137
Authors: Simon, A.; Fontaine, G.; Brassard, P.
Abstract: Since stellar helium thermonuclear burning is still not well constrained, the exact proportion of carbon and oxygen in the core of white dwarfs remains largely unknown. Given that the cooling time of these objects depends on their composition, it is thus crucial to constrain the latter in order to use white dwarfs as cosmochronometers. To address this, we compared theoretical luminosty functions built for a wide range of compositions to the observed luminosity function of the coeval white dwarfs in the M67 cluster. Theoretical luminosity functions were determined from 300 state-of-the-art evolutionary sequences, combined with models for the stellar formation rate, initial mass function, and initial-to-final mass relationship. Since the age of M67 is known to a good precision , this comparison allowed us to determine the mean carbon-to-oxygen ratio of its white dwarf population. Assuming that the white dwarfs in M67 are 80% DA's and 20% DB's with standard "thick" envelopes, we find that their core composition is dominated by oxygen.
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