The effects of diffusion due to gravity and due to composition gradients on the rate of hydrogen burning in a cooling degenerate dwarf. I - The case of a thick helium buffer layer

Details The effects of diffusion due to gravity and due to composition gradients on the rate of hydrogen burning in a cooling degenerate dwarf. I - The case of a thick helium buffer layer The effects of diffusion due to gravity and due to composition gradients on the rate of hydrogen burning in a cooling degenerate dwarf. I - The case of a thick helium buffer layer

Sep 1985

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985apj...296..540i&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 296, Sept. 15, 1985, p. 540-553.

Astronomy and Astrophysics

Astrophysics

112

Astrophysics, Stellar Composition, Stellar Evolution, Surface Layers, White Dwarf Stars, Buffers, Burning Rate, Diffusion Theory, Gravitation Theory, Helium, Strata

Scientific paper

The evolution of an isolated carbon-oxygen degenerate dwarf which has a surface layer initially containing hydrogen and helium and is of mass 0.6 M_sun; is followed from the planetary nebula nucleus stage at a luminosity of 5×103L_sun; until luminosity drops to 10-5L_sun;. Wind mass loss and accretion from the interstellar medium are neglected. Shortly after the model reaches a maximum surface temperature of about 1.5×105K, CN cycle reactions cease abruptly to contribute dominantly to surface luminosity, which drops to below 100 L_sun;. However, hydrogen-burning reactions continue to take place. The effect of diffusion induced by gravity forces and by composition gradients on the contribution of hydrogen burning to surface luminosity is studied. The total amount of hydrogen left in surface layers after 1010yr of cooling is about 1.4×10-4M_sun;, compared with a value of about 2.1×10-4M_sun; obtaining at the point of maximum surface temperature. Thus, diffusion and nuclear burning cannot reduce the mass of hydrogen in surface layers to below 10-7M_sun;, as demanded by a current interpretation of the light variations of ZZ Ceti stars.

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