Late-type giants with infrared excess
I. Lithium abundances *
G. Jasniewicz 1,
M. Parthasarathy 1,2,
P. de Laverny 1,3 and
F. Thévenin 3
Received 25 August 1998 / Accepted 16 November 1998
de la Reza et al. (1997) suggested that all K giants become Li-rich for a short time. During this period the giants are associated with an expanding thin circumstellar shell supposedly triggered by an abrupt internal mixing mechanism resulting in the surface Li enrichment. In order to test this hypothesis 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 connection between the circumstellar shells and Li abundance. Eight giants have been found to have log (Li) 1.0. In the remaining giants the Li abundance is found to be much lower.
HD 219025 is found to be a rapidly rotating (projected rotational velocity of 23 km s-1), dusty and Li-rich (log (Li) = ) K giant. Absolute magnitude derived from the Hipparcos parallax reveals that it is a giant and not a pre-main-sequence star. The evolutionary status of HD 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 abundance of Li is not preserved. There seems to be no correlations between Li abundances, rotational velocities and carbon isotope ratios. The only satisfactory explanation for the overabundance of lithium in these giants is the creation of Li by the extra deep mixing and the associated "cool bottom processing".
Key words: stars: abundances stars: circumstellar matter stars: evolution stars: individual: HD 219025 stars: late-type infrared: stars
Send offprint requests to: G. Jasniewicz
Note added in Proof: Recently Fekel & Watson (AJ in press) also searched for Li-rich giants among stars with infrared excess from the list of Zuckerman et al. (1995).
© European Southern Observatory (ESO) 1999
Online publication: February 23, 1999