Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 1977
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1977a%26a....54..499m&link_type=abstract
Astronomy and Astrophysics, vol. 54, no. 2, Jan. 1977, p. 499-503.
Astronomy and Astrophysics
Astrophysics
5
Convective Heat Transfer, Mixing Length Flow Theory, Stellar Atmospheres, White Dwarf Stars, Atmospheric Models, Cooling, Equations Of State, Stellar Envelopes, Stellar Models
Scientific paper
Convection-zone models for 4670-A white dwarfs (actually helium stars) with a surface gravity of 100 million cm/sec per sec are computed over the temperature range from 6500 to 10,000 K and are compared with similar models computed for 'normal' (i.e., carbon-poor) cool non-DA stars. The hydrodynamics is described by mixing-length theory, and effects of partial degeneracy and pressure ionization are taken into account in the buoyancy terms of the equation of motion as well as in the calculations of the density-pressure-temperature relation, the adiabatic gradient, the specific heat, and the scale height. Results are presented in terms of the temperature, pressure, and density at the top of the convection zone and the temperature, pressure, density, degeneracy parameter, geometrical depth, and degree of He ionization at the lower boundary. It is shown that: (1) the convection zones of 4670-A stars are thinner than those of 'normal' non-DA stars with the same effective temperature; (2) the degree of degeneracy at the bottom of the convection zone is higher in the 'normal' stars; (3) the atmospheric opacity in 4670-A stars is higher, due mostly to increased He(-) absorption; (4) the core temperatures and cooling times of the two types of stars are markedly different; and (5) convective velocities and acoustic fluxes are appreciably greater for the 4670-A stars.
Boehm Karl-Heinz
Muchmore David O.
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