On the Spectral Evolution of Hot White Dwarf Stars. I. A Detailed Model-Atmosphere Analysis of Hot White Dwarfs from SDSS DR12

Understand

As they evolve, white dwarfs undergo major changes in surface composition, a phenomenon known as spectral evolution.

• In particular, some stars enter the cooling sequence with helium atmospheres (type DO) but eventually develop hydrogen atmospheres (type DA), most likely through the upward diffusion of residual hydrogen.
• Our empirical knowledge of this process remains scarce: the fractions of white dwarfs that are born helium-rich and that experience the DO-to-DA transformation are poorly constrained.
• We tackle this issue by performing a detailed model-atmosphere investigation of 1806 hot ($T_{\rm eff} \ge 30,000$ K) white dwarfs observed spectroscopically by the Sloan Digital Sky Survey.