A SURVEY OF LITHIUM IN THE RED GIANTS OF THE MAGELLANIC CLOUDS

摘要

A spectroscopic search for the Li I 6707 A resonance line has been carried out in 112 red giants from both the Small and Large Magellanic Clouds. The spectra are a mixture of high- (R = λ/Δλ = 18,000) and low-resolution (R = 4000) data, and the stars surveyed consist of spectral types M, S, and C. Most of these stars have absolute bolometric magnitude, M_(bol), determinations available from various published investigations. The Li I line is detected in 35 of these red giants (29 S stars and six C stars). All stars with a measurable Li I feature are asymptotic giant branch (AGB) stars with the majority (26) being luminous S stars within the narrow luminosity range of -7.2 approx< M_(bol) approx< 6.0 (M_(bol) = -6.52 ± 0.38 in this subset of the stars). Abundance estimates of lithium in these stars fall in the range of log ε(Li) ～ 1.0-4.0. The presence of Li in these highly evolved AGB stars is ascribed to hot-bottom convective envelope (HBCE) burning and a comparison of the Li abundances derived here with published models of HBCE shows reasonably good agreement.