I am interested in the study of white dwarf stars and, in particular, the calculation of model atmospheres. White dwarf stars represent the final evolutionary stage of more than 97% of stars in our galaxy, including our Sun. Having exhausted the nuclear power sources in their centre, white dwarfs cool slowly over several billion years. They have a mass comparable to that of the Sun but in a volume equal to that of the Earth, thus making them extremely compact objects whose density is a million times that of the Sun. The study of these stellar remnants and the determination of their fundamental parameters such as surface temperature, mass and chemical composition tell us not only about the nature of these stars, but also about the evolutionary link with the stars that produced them. The most accurate method for measuring the basic parameters of white dwarf stars is to compare in detail the spectroscopic data, i.e. the flux distribution as a function of wavelength, with theoretical predictions obtained from model atmospheres we have been constantly refining here at the Université de Montréal. The stellar atmosphere corresponds to the thin surface layer where the stellar radiation originates. I am also interested in the study of pulsating white dwarfs, called ZZ Ceti stars, and in particular the determination of the empirical boundaries of their instability strips. All of these theoretical projects rely on photometric and spectroscopic data obtained at different observatories at Kitt Peak in Arizona (2.3 m Steward, 2.1 m and 4 m Kitt Peak) and the Mont Mégantic Observatory.