Open AccessDiffusion in helium white dwarf stars
Author(s) -
Althaus L. G.,
Benvenuto O. G.
Publication year - 2000
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2000.03825.x
Subject(s) - white dwarf , physics , black dwarf , astrophysics , stellar evolution , helium , blue dwarf , effective temperature , ambipolar diffusion , diffusion , astronomy , stars , thermodynamics , atomic physics , plasma , nuclear physics
This paper is aimed at exploring the effects of diffusion on the structure and evolution of low‐mass helium white dwarfs. To this end, we solve the multicomponent flow equations describing gravitational settling and chemical and thermal diffusion. The diffusion calculations are coupled to an evolutionary code in order to follow the cooling of low‐mass, helium core white dwarf models having envelopes made up of a mixture of hydrogen and helium, as recently suggested by detailed evolutionary calculations for white dwarf progenitors in binary systems. We find that diffusion causes hydrogen to float and the other elements to sink over time‐scales shorter than evolutionary time‐scales. This produces a noticeable change in the structure of the outer layers, making the star inflate. Thus, in order to compute accurately the mass–radius relation for low‐mass helium white dwarfs we need to account for the diffusion processes during (at least) the white dwarf stages of the evolution of these objects. This should be particularly important when studying the general characteristics of binary systems containing a helium white dwarf and a pulsar. In addition, we present an analytic, approximate model for the outer layers of the white dwarf aimed at interpreting the physical reasons for the change in the surface gravity for low‐mass white dwarfs induced by diffusion.