August 11-15, 2014


A study of the effects of metallicity on the population of Galactic disk white dwarfs

Ruxandra Cojocaru (Universitat Politècnica de Catalunya/BarcelonaTech)

Ruxandra Cojocaru1,2, Santiago Torres1,2, Jordi Isern3,2 and Enrique García–Berro1,2

1 Departament de Física Aplicada, Universitat Politècnica de Catalunya, c/Esteve Terrades 5, 08860 Castelldefels, Spain

2 Institute for Space Studies of Catalonia, c/Gran Capità 2–4, Edif. Nexus 104, 08034 Barcelona, Spain

3 Institut de Ciències de l’Espai (CSIC), Campus UAB, Facultat de Ciències, Torre C-5 08193 Bellaterra, Spain

It is well established that when using main sequence evolutionary tracks stellar metallicity has a significant impact on the determination of the ages of different Galactic stellar populations. Here we study the role that metallicity plays on the age estimation for the Galactic disk when using the white dwarf luminosity function. We use a Monte Carlo population synthesis code that models the population of disk white dwarfs. Our code includes 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 test two different models for the evolution of metallicity, one where the metallicity is constant in time, but has a moderate dispersion, and a second model in which the metallicity increases with time. We find that, independently of the adopted age-metallicity law, our simulated white dwarf luminosity functions are in very good agreement with the luminosity functions derived from the Sloan Digital Sky Survey (SDSS) and from the SuperCOSMOS Sky Survey (SSS). We find that the age-metallicity law has no noticeable impact on the shape of the bright branch of the white dwarf luminosity function. Thus, it can be concluded that this branch can be safely employed to test the theoretical evolutionary sequences. Also, we find that the location of the cut-off in the luminosity function is almost insensitive to the adopted age-metallicity relation. This ensures that its position can be used as a robust indicator of the age of the Galactic disk.

Mode of presentation: poster