Hydrogenic radiative recombination at low temperature and density

Abstract

The radiative recombination of hydrogenic ions is calculated in the limit of low density by the nl-method, extending the results of Pengelly (1964) to much lower temperatures (both case A and case B). A strong motivation is the detection of the emission-line spectrum of the old shell of Nova DQ Her 1934 reported by Williams et al. (1978), which revealed an electron temperature T(e) of about 500 K. The results are compared with the 1959 result of Seaton using the n-method, with those of Hummer and Storey (1987), which allow for the effects of collisions at finite density, and with the data for three cold old nova shells. Another motivation is the detection of relatively strong optical radiative recombination lines of C, N, and O in these shells. The abundances of these elements (recombining ions of charge Z) can be derived using a hydrogenic approximation to the effective radiative recombination coefficients, requiring the recombination coefficients of H(+) at even lower temperatures. 27 references.