Astronomy and Astrophysics – Astronomy
Scientific paper
May 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...180.5903v&link_type=abstract
American Astronomical Society, 180th AAS Meeting, #59.03; Bulletin of the American Astronomical Society, Vol. 24, p.824
Astronomy and Astrophysics
Astronomy
1
Scientific paper
In post-main-sequence phases of stellar evolution, densities in the interiors of stars become large enough so that hbar omega_p /kT>1, where omega_p is the electron plasma frequency. The plasma is thus a strongly dispersive medium at frequencies near the peak of the Planck function, and only photons with frequencies omega >omega_p can propagate in the plasma. These effects must be taken into account in computing radiative transfer in stellar interiors. Here I first identify several late evolutionary stages in which these effects may be significant. Then I use the formalism Harris 1965 has developed to treat radiative transfer in a dispersive medium in order to derive the resulting modification of the Rosseland mean opacity kappa_R . The resulting expression is the same as that presented (without a full derivation) by Aharony & Opher 1979, who interpreted the frequency-dependent absorption coefficient kappa_ ω as that in vacuo. However, the absorption coefficient in a plasma scales from that in vacuum according to the relation kappa_ ω=n_ω(-1) kappa_ ω((vac)) (Bekefi 1966, p. 52), where n_ω equiv (kc/omega ) = [1-(omega_p (2/) omega (2)right ](1/2)) is the index of refraction of the plasma. With this correction, we find the Rosseland mean opacity to be given by the expression {1\over \kappa_R}={{\int_{\omega_p}^{\infty} {n_{\omega}^3 \over \kappa_{\omega}^{(vac)}}{partial B_{\omega} \over partial T} \bigg|_{\omega} d\omega} \over{\int_0^{\infty}{partial B_{\omega} \over partial T} \bigg|_{\omega} d\omega}}. This research has been supported in part by NASA grant NAGW-2444 and in part by NSF grant AST 91-15132. \centerline{References} Aharony, U., and Opher, R. 1979, A&A, 79, 27. Bekefi, G. 1966, Radiation Processes in Plasmas, (John Wiley & Sons, Inc.: New York). Harris, E. G. 1965, Phys. Rev., 138, B479.
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