Abstract:

This dissertation focuses on white dwarf stars with some hydrogen, that possess a mass of surface hydrogen from 1 x 10-11 [Special characters omitted.] to 1 x 10-7 [Special characters omitted.] . The chemical structure of such white dwarfs is mainly controlled by convection and has never been studied in a fully proper manner. We present the first comprehensive study of such objects, including: (1) The relation between surface chemical composition and stellar structure. (2) The cooling curve and curve of surface chemical evolution. (3) The "Teff function" of the galactic disc derived from such cooling curves.

The study enables us to: (1) Infer physical quantities such as total hydrogen mass (mH ) and core temperature ( Tcore ) from spectroscopy. (2) Understand the correlation between the non-DA to DA abundance ratio and Teff , such as the "non-DA gap" proposed by Bergeron, Ruiz, & Leggett (1997). (3) Better understand the cosmo-chronological meaning of the white dwarf luminosity function.