WIYN Open Cluster Study. LXXXI. Caught in the Act? The Peculiar Red Giant NGC 2243-W2135

Abstract

High-dispersion spectra for giants through turnoff stars in the Li 6708 Å region have been obtained and analyzed in the old, metal-deficient open cluster, NGC 2243. When combined with high-dispersion data from other surveys, the cluster is found to contain a uniquely peculiar star at the luminosity level of the red clump. The giant is the reddest star at its luminosity, exhibits variability at a minimum 0.1 mag level on a timescale of days, is a single-lined, radial-velocity variable, and has $v\sin i$ between 35 and 40 km s^-1. In sharp contrast with the majority of the red giant cluster members, the star has a detectable Li abundance, potentially as high or higher than other giants observed to date while at or just below the boundary normally adopted for Li-rich giants. The observed anomalies may be indicators of the underlying process by which the giant has achieved its unusual Li abundance, with a recent mass transfer episode being the most probable within the currently limited constraints.