Galactic evolution of Li-7: the interplay between Novae and AGB stars

摘要

The enrichment of Li-7 in the interstellar gas of the Galaxy is followed in the framework of a detailed model of chemical evolution. Two different astrophysical environments have been considered for the production of Li-7: Novae and intermediate-mass AGE stars thereafter IMS). We demonstrate that, despite of the uncertainties in the Novae studies, their contribution to the Galactic Li-7 enrichment is too low to account for the Li-7 solar abundance. On the other side, we show that the interplay between the Hot Bottom Burning process (occurring at the bottom of the convective envelope of IMS stars and responsible for the Li-7 production via the Cameron-Fowler mechanism (Cameron 1955)), and a very high mass-loss rate (see e.g. Vassiliadis & Wood 1993, hereafter VW), can have a significant impact on the enrichment of Li-7 in the Galaxy. These predictions are sustained by recent observations of dense circumstellar shells around OH/IR- or C-stars, suggesting the existence of the so-called superwind phase before the evolution off the AGE phase. Finally, our results are compared with a compilation of spectroscopic observations of Li-7 taken from literature and from our original data, including halo and disk stars as well as young clusters. [References: 19]