Metallicity distribution and abundance ratios in the stars of the Galactic bulge

Abstract

Using chemical evolution models, it is shown that the metallicity distribution of bulge K giants can be very well reproduced under the relatively simple assumptions. These are: fast evolution characterized by a fast collapse, a very efficient star-formation rate relative to the solar vicinity region, and an initial mass function (IMF) with a slightly lower power index than the Salpeter one. Numerical experiments are reported which show that the range of variation for the star-formation efficiency and the time scale of formation of the system needed to reproduce the main characteristics of bulge stars is quite narrow. The major uncertainty resides in the IMF. A prediction is made of the abundance ratios of alpha elements with respect to iron which should be found in bulge stars, and which are independent of adopted IMF.