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The Penn State - Torun Centre for Astronomy Planet Search stars. II. Lithium abundance analysis of the Red Giant Clump sample

Using the sample of 348 stars from the PennState-Torun Centre for Astronomy Planet Search, for which uniformly determined atmospheric parameters are available, with chemical abundances and rotational velocities presented here, we investigate various channels of Li enrichment in giants. Our work is based on the HET/HRS spectra. The A(Li) was determined from the 670.8nm line, while we use a more extended set of lines for alpha-elements abundances. In a series of K-S tests, we compare Li-rich giants with other stars in the sample. We also use available IR photometric and kinematical data in search for evidence of mass-loss. We investigate properties of the most Li-abundant giants in more detail by using multi-epoch precise radial velocities. We present Li and alpha-elements abundances, as well as vsini for 348 stars. We detected Li in 92 stars, of which 82 are giants. 11 of them show significant Li abundance A(Li)>1.4 and 7 of them are Li-overabundant objects, according to criterion of A(Li)>1.5 and their location on HR diagram, including two giants with Li abundances close to meteoritic level. For another 271 stars, upper limits of A(Li) are presented. We show that Li-rich giants are among the most massive stars from our sample and show larger than average effective temperatures. They are indistinguishable from the complete sample in terms of their distribution of luminosity, [Fe/H], vsini, and alpha-elements abundances. Our results do not point out to one specific Li enrichment mechanism operating in our sample of giants. On the contrary, in some cases, we cannot identify fingerprints of any of known scenarios. We show, however, that the 4 most Li-rich giant in our sample either have low-mass companions or have RV variations at the level of ~100 m/s, which strongly suggests that the presence of companions is an important factor in the Li-enrichment processes in giants.