Physical conditions in the cool parts of prominences. III The Sr(+)/Ba(+) resonance line ratios and the internal Lyman-alpha flux

Abstract

This is the latest in a series of contributions devoted to the determination of the physical properties of the low-temperature material in prominences and spicules, emphasizing a detailed spectrophotometric analysis of the metal line emission. In this paper we use the differential effect of h Ly..cap alpha.. on the ionization balance in Sr/sup +/ and Ba/sup +/ to provide a measure of the internal Ly..cap alpha.. field in quiescent prominences. The statistical equilibria for these ions have been recomputed using expanded model atoms and new photoionization cross sections obtained according to a scaled Thomas-Fermi method with core polarization effects included. To help asses the accuracy of our photoionization results, we also calculate a large number of oscillator strengths for these ions. These are seen to compare favorably with the available experimental values, and to be considerably better for a number of Ba/sup +/ transitions where other theoretical values are severely discrepant. The calculated n(Ba/sup +/ 6 /sup 2/P/sub J/)/n(Sr/sup +/ 5 /sup 2/P/sub J/) level population ratios are used to interpret Ba/sup +/ and Sr/sup +/ resonance line intensity measurements made in a large number of prominences at Haleakala, with the result that our previous estimates for the internal Ly..capmore » alpha.. intensity are indeed appropriate. In particular, E(Ly..cap alpha..) is not large enough to substantially affect the application of our Na/Sr/sup +/ and Mg/Sr/sup +/ diagnostic line ratios, and our previous spectral analyses are satisfactory as they stand. These conclusions are further confirmed with additional Na and Sr/sup +/ resonance line data, again obtained at Haleakala.« less