Convective white-dwarf envelope model grids for H-, He-, and C-rich compositions.
Abstract
We have computed models of hydrogen-, helium-, and carbon-rich white-dwarf envelopes, with element abundances XH = 0.999, XHe = 0.999, and X0 = 0.999, respectively, and with masses and luminosities in the ranges 0.22 < MIM0 < 1.22 and -4.0 < log LIL0 < -1.5. An important feature of our calculations is the use of a thermodynamically consistent equation of state for the partial ionization zone. Convection is taken into account through the mixing-length theory, and the structures and systematics of the white-dwarf convection zones are described in detail. For a given stellar mass and composition, we flnd that the convection zone grows inward from the surface, following the region of partial ionization, until the base of the zone becomes degenerate. Pressure ionization and the high efficiency of electron conduction tend to suppress convection. The base of the convective region is thus pushed outward toward the surface as the degeneracy increases further, with decreasing luminosity. The convection zones of He- and C-rich envelopes are invariably more extensive than in the H-rich cases due to the greater extent of the partial ionization region in a high-Z envelope. Convective velocities are typically 0.1-1.0 km s -1, and are sensitive to mass, luminosity, and composition. Only in models where the convection zone extends into the degenerate core is the core temperature significantly lower, for a given luminosity, than for models in pure (forced) radiative equilibrium. In none of our models was the core temperature decreased by more than 50 percent, however. Subject headings: convection - stars: interiors - stars: white dwarfs
- Publication:
-
The Astrophysical Journal Supplement Series
- Pub Date:
- July 1976
- DOI:
- 10.1086/190388
- Bibcode:
- 1976ApJS...31..467F
- Keywords:
-
- Carbon Stars;
- Stellar Envelopes;
- Stellar Models;
- White Dwarf Stars;
- Astrophysics;
- Convective Heat Transfer;
- Helium;
- Hydrogen;
- Astrophysics