Abstract

The inclusion of a detailed treatment of solidification processes in the cooling theory of carbon–oxygen white dwarfs is of crucial importance for the determination of their luminosity function. Carbon–oxygen separation at crystallization yields delays larger than 2 Gyr to cool down to luminosities corresponding to the observed cut–off. This leads to estimates of the age of the galactic disk 1.5 to 2 Gyr older than the ones obtained in previous studies (about 9 Gyr). Furthermore, the presence of minor chemical species, in particular 22Ne, alters significantly the crystallization process, and produces extra delays of 2 to 3 gigayears. However, the detailed computation of the theoretical white dwarf luminosity function, taking into account a reasonable model of galactic chemical evolution, and including the effect of these species, shows that the location of the cut–off, and then the estimated age of the disk, is not modified significantly.

Le traitement détaillé du processus de solidification revêt une importance cruciale dans l'étude du refroidissement des naines blanches carbone–oxygéne et la détermination de leur fonction de luminosité. La séparation du carbone et de l'oxygène lors de la cristallisation introduit un retard de plus de 2 109 ans pour atteindre les valeurs de la luminosité correspondant au cut–off observé. Ceci conduit à une estimation de l'âge du disque de 1.5 à 2 109 ans plus vieille que celles obtenues dans les études précédentes.