The effects of metallicity on the Galactic disk population of white dwarfs

Abstract

It has been known for a long time that stellar metallicity plays a significant role in the determination of the ages of the different Galactic stellar populations, when main sequence evolutionary tracks are employed. Here we analyze the role that metallicity plays on the white dwarf luminosity function of the Galactic disk, which is often used to determine its age. We employ a Monte Carlo population synthesis code that accounts for the properties of the population of Galactic disk white dwarfs. Our code incorporates the most up-to-date evolutionary cooling sequences for white dwarfs with hydrogen-rich and hydrogen-deficient atmospheres for both carbon-oxygen and oxygen-neon cores. We use two different models to assess the evolution of the metallicity, one in which the adopted metallicity is constant with time, but with a moderate dispersion, and a second one in which the metallicity increases with time. We found that our theoretical results are in a very satisfactory agreement with the observational luminosity functions obtained from the Sloan Digital Sky Survey (SDSS) and from the SuperCOSMOS Sky Survey (SSS), independently of the adopted age-metallicity law. In particular, we found that the age-metallicity law has no noticeable impact in shaping the bright branch of the white dwarf luminosity function, and that the position of its cut-off is almost insensitive to the adopoted age-metallicity relationship. Because the shape of the bright branch of the white dwarf luminosity function is insensitive to the age-metallicity law, it can be safely employed to test the theoretical evolutionary sequences, while due to the limited sensitivity of the position of the drop-off to the distribution of metallicities, its location provides a robust indicator of the age of the Galactic disk.

7 pages, 5 figures, accepted for publication in A&A

References in corpus (10)

• The 2.5 m Telescope of the Sloan Digital Sky Survey
• New constraints on the chemical evolution of the solar neighbourhood and Galactic disc(s). Improved astrophysical parameters for the Geneva-Copenhagen Survey
• Empirical Color Transformations Between SDSS Photometry and Other Photometric Systems
• The initial-final mass relationship of white dwarfs revisited: effect on the luminosity function and mass distribution
• Radial mixing and the transition between the thick and thin Galactic discs
• Axions and the cooling of white dwarf stars
• White Dwarf Luminosity and Mass Functions from Sloan Digital Sky Survey Spectra
• The white dwarf luminosity function. I. Statistical errors and alternatives
• The structure of the Galactic halo: SDSS versus SuperCOSMOS
• The white dwarf luminosity function --II. The effect of the measurement errors and other biases

Cited by in corpus (6)

• A comparison of gyrochronological and isochronal age estimates for transiting exoplanet host stars
• Bayesian mass and age estimates for transiting exoplanet host stars
• The white dwarf luminosity function
• The population of white dwarf-main sequence binaries in the SDSS DR 12
• DA white dwarfs from the LSS-GAC survey DR1: the preliminary luminosity and mass functions and formation rate
• An independent test of the photometric selection of white dwarf candidates using LAMOST DR3