Synthesis of Lithium and s-Process Elements in Small Magellanic Cloud Asymptotic Giant Branch Stars
Abstract
High-resolution spectroscopy is presented for five luminous (M_bol_ ~ -6 to -7) asymptotic giant branch (AGB) stars in the Small Magellanic Cloud (SMC). These stars are found to be metal-poor ([Fe/H] ~ -0.5) but s-process-enriched, relative to Fe-peak elements, by up to a factor of 10: these are s-process enhancements that are comparable to those observed in Galactic S stars; thus, these SMC AGB stars have experienced a third dredge-up. Of more interest is the fact that all five red giants have rather strong Li I resonance lines (6707 A); an abundance analysis reveals these stars to have Li abundances that are 100-1000 times that expected in red giants. We argue that these very luminous (and probably massive) AGB stars have synthesized Li as predicted by certain stellar models of hot-bottom convective-envelope burning. We discuss the observations and models as a basis for understanding certain phases of red giant evolution and as a potentially significant source of Li in the universe.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 1989
- DOI:
- 10.1086/185556
- Bibcode:
- 1989ApJ...345L..75S
- Keywords:
-
- Abundance;
- Asymptotic Giant Branch Stars;
- Late Stars;
- Magellanic Clouds;
- Nuclear Fusion;
- Red Giant Stars;
- Astronomical Spectroscopy;
- Lithium;
- Quantitative Analysis;
- Stellar Evolution;
- Zirconium Oxides;
- Astrophysics;
- ABUNDANCES;
- NUCLEOSYNTHESIS;
- STARS: ABUNDANCES;
- STARS: LATE-TYPE