Diffusion and hydrogen shell burning on slowly accreting white dwarfs

Journal Article · Tue Jun 01 00:00:00 EDT 1982 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/159989· OSTI ID:6770838

Fujimoto, M Y; Truran, J W

The stability of hydrogen shell burning in accreted envelopes on white dwarfs is examined for the domain of low accretion rates. Account is taken of the effects of diffusion of CNO nuclei attributable to sedimentation associated with gravity and temperature gradients. Due to the direct competition with accretion, the effects of such sedimentation of CNO elements become important only for accretion rates smaller than M = 10/sup -11/ M/sub sun/ yr/sup -1/, for hydrogen shell burning in steady state approximation. Such a steady state is stable, for white dwarfs of mass < or approx. =M/sub sun/, in a narrow range of accretion rates around M = 10/sup -12/ M/sub sun/ yr/sup -1/; this results from the weak temperature dependences of the proton-proton cycles and the relatively weak degeneracy at the burning shell. Reduction of CNO abundance levels due to sedimentation acts to enlarge this accretion rate range by approximately a factor of 2. The stable steady state is realized only when gas is accreted onto a hot white dwarf. For accretion onto cool white dwarfs, the stable regime is bypassed by recurrent shell flashes. In this latter case, the concentration of CNO elements will not be greatly affected by sedimentation because of its low efficiency at the low temperatures characterizing the accretion phase.

• Research Organization: Department of Astronomy, University of Illinois
• OSTI ID: 6770838
• Journal Information: Astrophys. J.; (United States), Vol. 257:1
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
WHITE DWARF STARS
DIFFUSION
HYDROGEN BURNING
STABILITY
STAR ACCRETION
STAR EVOLUTION
STAR MODELS
CARBON
HYDROGEN
NITROGEN
OXYGEN
DWARF STARS
ELEMENTS
MATHEMATICAL MODELS
NONMETALS
STAR BURNING
STARS
640102* - Astrophysics &amp; Cosmology- Stars &amp; Quasi-Stellar
Radio &amp; X-Ray Sources