2020/08/17 by A. Bédard, P. Bergeron, P. Brassard +1 · 319 citations
Physics and Astronomy · Social Sciences · #Astronomy and Astrophysical Research #Atmosphere (unit) #Educational Leadership and Practices #Effective temperature #Main sequence #Sky #Spectral line #Stars #Stellar atmosphere #Stellar classification #Stellar, planetary, and galactic studies #White dwarf #astro-ph.SR
paper · pdf · open access · doi:10.3847/1538-4357/abafbe
published in The Astrophysical Journal 901(2), 93 (IOP Publishing) · 33 pages (plus a 49-page table), 20 figures, accepted for publication in The Astrophysical Journal
arxiv created 2020/08/17 · openalex created_date 2020/08/21 · openalex publication_date 2020/09/25 · arxiv updated 2020/10/07 · openalex updated_date 2026/08/05
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 ≥ 30,000 K) white dwarfs observed spectroscopically by the Sloan Digital Sky Survey. We first introduce our new generations of model atmospheres and theoretical cooling tracks, both appropriate for hot white dwarfs. We then present our spectroscopic analysis, from which we determine the atmospheric and stellar parameters of our sample objects. We find that ∼24% of white dwarfs begin their degenerate life as DO stars, among which ∼2/3 later become DA stars. We also infer that the DO-to-DA transition occurs at substantially different temperatures (75,000 \rm K > T\rm eff > 30,000 K) for different objects, implying a broad range of hydrogen content within the DO population. Furthermore, we identify 127 hybrid white dwarfs, including 31 showing evidence of chemical stratification, and we discuss how these stars fit in our understanding of the spectral evolution. Finally, we uncover significant problems in the spectroscopic mass scale of very hot (T\rm eff > 60,000 K) white dwarfs.