The effects of ${}^{22}$Ne sedimentation and metallicity on the local 40 pc white dwarf luminosity function

Abstract

We analyze the effect of the sedimentation of ${}^{22}$Ne on the local white dwarf luminosity function by studying scenarios under different Galactic metallicity models. We make use of an up-to-date population synthesis code based on Monte Carlo techniques to derive the synthetic luminosity function. Constant solar metallicity models are not able to simultaneously reproduce the peak and cut-off of the white dwarf luminosity function. The extra release of energy due to ${}^{22}$Ne sedimentation piles up more objects in brighter bins of the faint end of the luminosity function. The contribution of a single burst thick disk population increases the number of stars in the magnitude interval centered around $M_{\mathrm{bol}}=15.75$. Among the metallicity models studied, the one following a Twarog's profile is disposable. Our best fit model was obtained when a dispersion in metallicities around the solar metallicity value is considered along with a ${}^{22}$Ne sedimentation model, a thick disk contribution and an age of the thin disk of $8.8\pm 0.2$ Gyr. Our population synthesis model is able to reproduce the local white dwarf luminosity function with a high degree of precision when a dispersion in metallicities around the solar value model is adopted. Although the effects of ${}^{22}$Ne sedimentation are only marginal and the contribution of a thick disk population is minor, both of them help in better fitting the peak and the cut-off regions of the white dwarf luminosity function.

11 pages, 9 figures and 2 tables; accepted for publication in A&A

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