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Light and heavy elements in the galactic bulge
Francesca Matteucci 1,2,
Donatella Romano 1,2 and
Paolo Molaro 3
Received 10 September 1998 / Accepted 20 October 1998
In the context of an inside-out model for the formation of our Galaxy we present results for the chemical evolution of the Galactic bulge by assuming that this central region evolved even faster than the Galactic halo. This assumption is required in order to reproduce the observed metallicity distribution of bulge stars as obtained by McWilliam & Rich (1994).
The model is similar to that adopted by Matteucci and Brocato (1990) with the exception that we have adopted the most recent nucleosynthesis prescriptions for either low-intermediate mass stars or massive stars and extended our predictions to most of the -elements, Fe, C, N and light elements (D, 7Li). We have tested the effect of changing the slope of the IMF on the predicted stellar metallicity distribution for bulge stars and have compared our results with the distribution obtained from the most recent data. An initial mass function (IMF) favoring the formation of massive stars with respect to the solar vicinity improves the agreement with observations. Then, using our best model, we have made some predictions about temporal evolution of light and heavy species in the Galactic bulge. In particular, we predict that -elements should be enhanced relative to Fe for most of the metallicity range, although different -elements should show a different degree of enhancement due to the particular nucleosynthetic history of each element. The enhancements are larger than predicted for the halo and thick-disk stars because of the flatter IMF assumed for the bulge. We predict that deuterium, due to the intense star formation occurred in bulge, should be completely depleted whereas 7Li should show a trend similar to that found for the solar neighbourhood. We also compared the Li abundance recently measured in one bulge star (Minniti et al., 1998) and concluded that it is very likely that the Li in the star must have been depleted and therefore it does not reflect the Li abundance of the gas out of which the star formed. In the opposite case, one should completely suppress one of the main stellar sources of Li in order to reconcile the model with the observed value.
Key words: nuclear reactions, nucleosynthesis, abundances Galaxy: evolution
Send offprint requests to: F. Matteucci
Online publication: December 4, 1998