W. J. Maciel -
Abstract #135
THE STAR FORMATION RATE IN THE MILKY WAY: RESULTS FROM STARS AND PLANETARY NEBULAE
W. J. Maciel, H. J. Rocha-Pinto, R. D. D. Costa
IAU Symposium No. 284, Ed. R.J. Tuffs, C.C. Popescu, CUP, 379-381 (2012) Recent determinations of Li abundances in the Galaxy resulted in two important conclusions: first, there is a significant discrepancy between the predicted values by Standard Big Bang Nucleosynthesis (SBBN) and the observed values, reaching about 0.6 dex for the oldest, most metal-poor stars; second, for these stars there seems to exist an almost linear relationship between the Li abundances relative to H and the metallicity as given by the Fe abundances relative to the Sun. Concerning higher metallicity objects, present results show that a larger dispersion of Li abundances is observed for a given metallicity up to about [Fe/H] 0.5. In the case of RGB and AGB stars, most of the objects analyzed have probably destroyed most of the pristine lithium. However, there is a number of galactic AGB and RGB stars, which show clear signs of Li enhancements, in particular those for which (Li) = 1.5, which are known as Li-rich giants. Since the metallicities of the Li-rich giants are generally known, it is interesting to investigate whether or not the trend presented by the metal-poor stars can also be observed in their metal-rich counterparts. This will provide a better understanding of the chemical evolution of lithium during the galactic lifetime, as well as place constraints on the Li production in AGB stars. In this work, we consider a large sample of AGB and RGB stars for which accurate Li abundances are available, and investigate the existence of any trends between the Li abundances and the metallicities. Our preliminary results suggest that, in average, Li-rich AGB stars maintain the same average increase of Li abundances at higher metallicities, so that a similar slope is obtained both for metal-poor and metal-rich stars. This has possibly some consequences on the mechanisms of Li production in AGB stars.
