HDE-233517 - LITHIUM AND EXCESS INFRARED-EMISSION IN GIANT STARS

Recent studies have identified a small class of moderately rapidly rot ating, chromospherically active, single giants, some of which are lith ium rich. We present evidence suggesting the peculiar K-type star HDE 233517 is one such object. Previously, HDE 233517 has been suggested t o be a young star, consistent with its large far-infrared excess and o ur log epsilon(Li) similar to 3.3. However, our high-resolution spectr oscopic observations show it is likely a single, post-main-sequence K2 giant with nu sin i = 15 km s(-1) and modest Ca II H and K emission. The giant status of HDE 233517 is determined directly from luminosity- sensitive line ratios and a lack of significant line wings, and is fur ther supported by a large radial velocity (46.5 km s(-1)), small prope r motion, and the presence of interstellar absorption features. Interp retation of the data in the context of a recent mass outflow model for giant stars proposed by de la Reza and coworkers indicates that HDE 2 33517 has the largest mass-loss rate, similar to 3 x 10(-7) M. yr(-1), of any known luminosity class III giant. We suggest that the processe s causing rapid rotation, large lithium abundance, and infrared excess are triggered at the base of the giant branch when the convection zon e reaches the rapidly rotating core of low-mass stars.