Diffusion-induced hydrogen burning in helium-rich white dwarfs

Details Diffusion-induced hydrogen burning in helium-rich white dwarfs Diffusion-induced hydrogen burning in helium-rich white dwarfs

May 1984

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984apj...280..247m&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 280, May 1, 1984, p. 247-254. Research supported by the Natural Sciences an

Astronomy and Astrophysics

Astrophysics

29

Hydrogen, Nuclear Fusion, Stellar Models, White Dwarf Stars, Atmospheric Composition, Helium, Steady State, Stellar Atmospheres, Stellar Cores, Stellar Mass Accretion, Turbulence Effects

Scientific paper

Even though diffusion concentrates hydrogen at the surface of white dwarfs, it is shown that the tail of the hydrogen abundance distribution extends deep enough for hydrogen to burn efficiently and quiescently in some of these stars. In the presence of nuclear burning, diffusion transports hydrogen from the superficial layers of white dwarfs to deeper regions where it is destroyed. The conditions under which this process is efficient in white dwarfs are examined, and, in particular, the process is applied to accreting helium-rich white dwarfs. This mechanism offers a natural explanation for the near absence of hydrogen in the atmospheres of helium-rich white dwarfs even if accretion of hydrogen-rich interstellar matter occurs onto those objects. It is shown that this process is most efficient in stars somewhat cooler than 30,000 K but hotter than 10,000 K. The main uncertainty in the calculations comes from the uncertainty in the interior temperature of white dwarfs. It is also shown that modest amounts of turbulence considerably increase the efficiency of this mechanism, effectively putting an upper limit on the presence of turbulence in white dwarfs. The discussion also covers the implications of the process for the spectral evolution of white dwarfs and, in particular, the transformation of some DA stars into DB objects.

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