Late-type giants with infrared excess - I. Lithium abundances

de la Reza et al. (1997) suggested that all K giants become Li-rich for a s hort time. During this period the giants are associated with an expanding t hin circumstellar shell supposedly triggered by an abrupt internal mixing m echanism resulting in the surface Li enrichment. In order to test this hypo thesis twenty nine late-type giants with far-infrared excess from the list of Zuckerman et al. (1995) were observed in the Li-region to study the conn ection between the circumstellar shells and Li abundance. Eight giants have been found to have log epsilon(Li) > 1.0. Ln the remaining giants the Li a bundance is found to be much lower. HD 219025 is found to be a rapidly rotating (projected rotational velocity of 23 +/- 3 km s(-1)), dusty and Li-rich (log epsilon(Li) = 3.0 +/- 0.2)K g iant. Absolute magnitude derived from the Hipparcos parallax reveals that i t is a giant and not a pre-main-sequence star. The evolutionary status of H D 219025 seems to be similar to that of HDE 233517 which is also a rapidly rotating, dusty and Li-rich K giant. The Hipparcos parallaxes of all the well studied Li-rich K giants show that most of them are brighter than the "clump" giants. Their position in the H -R diagram indicates that they have gone through mixing and the initial abu ndance of Li is not preserved. There seems to be no correlations between Li abundances, rotational velocities and carbon isotope ratios. The only sati sfactory explanation for the overabundance of lithium in these giants is th e creation of Li by the extra deep mixing and the associated "cool bottom p rocessing".