Lithium in a Cool Red Giant Member of the Globular Cluster NGC 362

A surprisingly strong Li I λ6707 feature has been identified in a red giant member of the globular cluster NGC 362. This giant, V2, is located near the tip of the red giant branch and could be either a first-ascent red giant or on the asymptotic giant branch. An abundance analysis finds the lithium abundance to be log(Li)=1.2±0.2. Since almost all low-mass giants have destroyed and diluted their photospheric lithium abundances to much lower levels, the source of lithium in star V2 is a mystery. The solution to this mystery is suggested to reside in two possible mechanisms. The proposed deep-mixing mechanism called "cool bottom processing" can account for the observed lithium at this giant's luminosity [log(L/L☉)=3.3] if the parameterized mixing speed, measured as log(dM/dt), is ~-5.5 (in units of M☉ yr-1). An alternative source of the excess lithium could be the ingestion, into the red giant's convective envelope, of an ~0.04 M☉ object with an assumed undepleted, typical halo lithium abundance of log(Li)=2.2.