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Paper: Cosmochronology in Action: Determination of the Mean Core Composition of the White Dwarfs in M 67
Volume: 469, 18th European White Dwarf Workshop (EUROWD12)
Page: 201
Authors: Simon, A.; Fontaine, G.; Brassard, P.
Abstract: As the rate of helium thermonuclear burning in stars remains uncertain, the exact proportions of carbon and oxygen in the cores of white dwarfs are still unknown. Given that the cooling time depends on such proportions, the luminosity functions for populations of white dwarfs with various compositions are not be the same. By comparing theoretical luminosity functions computed for populations of white dwarfs with different ratios of carbon and oxygen with the observed luminosity function of M 67 — a star cluster for which we have a precise knowledge of its age — we are able to infer the mean ratio of carbon-to-oxygen in the white dwarfs in that system. To obtain the theoretical luminosity functions, we computed some 100 state-of-the-art evolutionary sequences and combined the results with models of the stellar formation rate, the initial-to-final mass relationship, and the initial mass function. Under the assumption that the M 67 white dwarfs are all DA's with standard “thick” envelopes, we infer that the cores of these white dwarfs are dominated by oxygen.
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