New Model Sequences from the White Dwarf Evolution Code

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Abstract
Model sequences computed with the recently-published OPAL radiative opacities, Itoh et al. conductive opacities, and Itoh et al. neutrino rates are presented. Cooling times for DA model sequences are found to be independent of metallicity for Z ≤ 0.001. Introduction In the past decade, many improvements in the constitutive physics relevant to white dwarf evolutionary models have been published. These include improved radiative opacities (Rogers & Iglesias 1992; Iglesias & Rogers 1993), conductive opacities for pure (Itoh et al. 1993 and references therein) and mixed (Itoh & Kohyama 1993) compositions, and updated neutrino rates (Itoh et al. 1992 and references therein). We have incorporated these results into our white dwarf evolution code (=WDEC; see Lamb & Van Horn 1975, and Wood 1990), and present here selected C-core DA model sequences computed with the updated code. Stellar masses for the sequences are 0.4, 0.6, and 0.8 M ⊙ and surface layer masses are log q(H) = −6 and log q(He) = −4. To determine the effect of metallicity on the evolutionary timescale, we computed parallel sequences with Z = 0.000 and 0.001. Opacities The radiative opacities used in WDEC in the past (Cox & Stewart 1970) had an unrealistically-high metallicity of Z = 0.001 (Z obs ≲ 10−5) The new OPAL opacities span a wide range of metallicities and compositions, and therefore allow the inclusion of more plausible composition profiles in the models. The OPAL opacities only extend to a minimum temperature of 6000 K, however, so for DA models WDEC references the pure-H opacities of Lenzuni et al. (1991) below this point.
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