Stellar yields with rotation and their effect on chemical evolution models

We compute the evolution of different abundance ratios in the Milky Way (MW) for two different sets of stellar yields. In one of them stellar rotation is taken into account and we investigate its effects on the chemical evolution model predictions. Moreover, we show that some abundance ratios off er an important tool to investigate the halo-disk discontinuity. For the first time it is shown that the effect of a halt in the star formation between the halo / thick disk and thin disk phases, already suggested from studies based both on Fe/O vs. O/H and Fe/Mg vs. Mg/H, should also be seen in a C/O versus O/H plot if C is produced mainly by low- and intermediate-mass stars (LIMS). The idea that C originates mainly from LIMS is suggested by the flat behavior of the [C /Fe] ratio as a function of metallicity, from [Fe/H] similar to - 2.2 to solar, and by the fact that very recent C/O measurements for stars in the MW halo and disk seem to show a discontinuity around log (O/H) + 12 similar to 8 .4. Finally, a more gentle increase of N abundance with metallicity ( or time), relative to models adopting the yields of van den Hoek & Groenewegen (1997), is predicted by using the stellar yields of Meynet & Maeder (2002 - which include stellar rotation but not hot-bottom burning) for intermediate mass stars. This fact has some implications for the timescales of N enrichment and thus for the interpretation of the nature of Damped Lyman Alpha Systems.