Carbon Isotope Ratios for Giants in Globular Cluster M3: The Unique Lithium-Rich Giant IV-101

Abstract

Carbon isotope ratios have been determined in three giants in the globular cluster M3 observed with the NIRSPEC high-dispersion infrared spectrometer at the Keck Observatory, and in a fourth M3 giant observed with the Phoenix infrared spectrometer on the NOAO 4 m Mayall Telescope at Kitt Peak National Observatory. Abundances of iron, silicon, and titanium also have been derived for the three stars with NIRSPEC data. The derived atomic abundances are consistent with values in the literature for these stars. While three of the giants have 12C/13C ≈ 6 ± 1.5, typical of globular cluster giants, the carbon isotope ratio in the lithium-rich giant IV-101 is ≈11 ± 1.5, higher than that found in most other globular cluster giants of similar temperature. The Li and 12C/13C combination of IV-101 is consistent with a recent suggestion of anomalously energetic hydrogen shell fusion and mixing events in low-mass, low-metallicity stars on the first-ascent red giant branch.