Rapidly-rotating lithium-rich K giants: The new case of the giant PDS365

Abstract

PDS365 is a newly detected rapidly rotating (vsin i = 20 km/s) single low mass giant star which with HD233517 and HD219025 forms a remarkable ensemble of single K giants with the unique properties of rapid rotation, very strong Li lines, an asymmetrical Halpha profile, and a large far infrared excess. Their vsin i values are between 18 and 23 km/s, and LTE Li abundances, log e(Li), are between 2.9 and 3.9. Detailed analysis of PDS365 reveals it to be near one solar mass giant with a value of 12C/13C approximately equal to 12. A clear relation between high rotational velocities and very high Li abundances for K giant stars is found only when asymmetrical Halpha profiles and large far-infrared excesses are present. If we consider single K giants, we find that among rapid (vsin i >= 8 km/s) rotators, a very large proportion (~ 50%) are Li-rich giants. This proportion is in contrast with a very low proportion (~ 2%) of Li-rich stars among the much more common slowly rotating K giants. This striking difference is discussed in terms of proposed mechanisms for Li enrichment.