Abundance analyses of Li-enriched and normal giants in the GALAH survey

Abstract

Compositions of lithium-enriched and normal giants among the GALAH survey are compared. Except for Li, the only detectable abundance difference between lithium-enriched and normal giants among the investigated elements from carbon to europium occurs for carbon. Among Li-rich giants with A(Li) = 1.8–3.1, the C deficiency is very similar to that reported for the normal giants [with A(Li) < 1.8] where the slight C deficiency arises from the first dredge-up. Carbon is slightly underabundant relative to normal giants among the super Li-rich giants where the Li abundance exceeds A(Li) = 3.2. The C abundance as well as the 12C/13C ratios from the literature suggests that the addition of Li to create a Li-rich giant may occur independently of the abundance changes wrought by the first dredge-up. The creation of a super Li-rich giant, however, appears to occur with additional CN-cycle conversion of C to N. The probability of becoming a Li-rich giant is approximately independent of a star’s mass, although the majority of the Li-rich giants are found to be low mass (M ≤ 2 M⊙). The frequency of the occurrence of Li-enriched giants among normal giants is about 1 per cent and slightly dependent on metallicity ([Fe/H]). Li-enriched and normal giants are found to have similar projected rotational velocity, which suggests that Li enrichment in giants is not linked to scenarios such as mergers and tidal interaction between binary stars.