The coefficients of absorption and opacity of a partially degenerate gas

Abstract

1. The absorption of radiation in a highly degenerate gas has been investigated by Chandrasekhar, Majumdar, and the present writer. Chandrasekhar has also considered very fully the absorption in a classical gas. It appears that the absorption in a highly degenerate gas is much less than that which would be calculated for a classical gas at the same density and temperature. The present paper is concerned with the absorption in a gas for which the degeneracy, as measured by Sommerfeld’s parameter, is small. As in a stellar configuration with a degenerate-gas core there must be a transition zone, where the gas is only slightly degenerate, it may be of value for astrophysical purposes to know the behaviour of the absorption coefficient for incipient degeneracy. In 2 the coefficients of absorption and opacity due to “free-free” transitions are evaluated; in 3 and 4 the contributions to the atomic absorption coefficient due to “bound-free” transitions from the lower energy levels are calculated. In 5 the absorption coefficient per normal hydrogen atom is found and the mass absorption coefficient deduced, and in 6 the extrapolation for other atoms is discussed.