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Paper: Diffusion Calculations with Mass Loss in Hot White Dwarfs and Subdwarfs
Volume: 288, Stellar Atmosphere Modeling
Page: 637
Authors: Unglaub, K.; Bues, I.
Abstract: The combined effects of diffusion processes and weak winds have been investigated for hot white dwarfs on the upper cooling sequence with effective temperatures Teff > 50000 K and for subdwarf B stars in the range 25000 K ≤ Teff ≤ 40000 K. Within the outer stellar envelope characterized by mass depths < 10-2 M* for the elements H, He, C, N and O the equations of continuity and the momentum equations are solved simultaneously. So from a given initial composition the time evolution of the various abundances is predicted. Detailed opacity calculations allow to take into account the effect of the changing composition on the temperature structure. The winds are assumed to be chemically homogeneous and the mass loss rate dot M is considered as a free parameter.The results show that for subdwarf B stars weak winds with 10-14 ≤ dot M ≤ 1012 Modot / yr may explain the typical helium deficiencies and lead to abundance anomalies of heavy elements. In addition, according to the location of these stars in the Teff - log g diagram the existence of weak winds is plausible. For hot white dwarfs we expect the onset of gravitational settling when during the cooling process the mass loss rate decreases below about 10-11 Modot / yr. For a final clarification of the chemical evolution of hot white dwarfs theoretical mass loss rates from hydrodynamical model atmospheres are required.
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