The depletion of pre-interstellar matter and an examination of NI II oscillator strengths.

Abstract

IUE observations of the B2.5 V star α Sco B have been used to analyze the absorption lines that arise in the circumstellar shell around the M1.5 Iab star α Sco A. In addition to resonant lines of Fe II, Si II, Mg II, Mn II, and S II, most of the resonant lines of Ni II are also present at strengths above 40 mÅ. A fit of these Ni II lines to a curve of growth, established from the Fe II, Si II, and Mn II lines, shows that the oscillator strengths of Kurucz and Peytremann (1975) are good to within relative errors of ±50%. An analysis of the elemental abundances in the expanding preinterstellar material around α Sco A provides an opportunity to examine the depletions that arise from dust formation as this material expands and cools. The formation of circumstellar dust is considered one of the primary sources for the population of dust in the interstellar medium (Woolf 1973; Field 1974).