The evolution of the Milky Way from its earliest phases: Constraints on stellar nucleosynthesis

Abstract

We computed the evolution of the abundances of O, Mg, Si, Ca, K, Ti, Sc, Ni, Mn, Co, Fe and Zn in the Milky Way. We made use of the most widely adopted nucleosynthesis calculations and compared the model results with observational data with the aim of imposing constraints upon stellar yields. To best fit the data in the solar neighborhood, when adopting the Woosley & Weaver (1995, ApJS, 101, 181) yields for massive stars and the Iwamoto et al. (1999, ApJS, 125, 439) ones for type Ia SNe, it is required that: i) the Mg yields should be increased in stars with masses from 11 to 20 Mand decreased in masses larger than 20 M� . The Mg yield should be also increased in SNe Ia. ii) The Si yields should be slightly increased in stars above 40 M� , whereas those of Ti should be increased between 11 and 20 Mand above 30 M� . iii) The Cr and Mn yields should be increased in stars with masses in the range 11-20 M� ; iv) the Co yields in SNe Ia should be larger and smaller in stars in the range 11-20 M� ; v) the Ni yield from type Ia SNe should be decreased; vi) the Zn yield from type Ia SNe should be increased. vii) The yields of O (metallicity dependent SN models), Ca, Fe, Ni, and Zn (the solar abundance case) in massive stars from Woosley & Weaver (1995) are the best to fit the abundance patterns of these elements since they do not need any changes. We also adopted the yields by Nomoto et al. (1997, Nucl. Phys. A, 621, 467) and Limongi & Chieffi (2003, ApJ, 592, 404) for massive stars and discuss the corrections required in these yields in order to fit the observations. Finally, the small spread in the (el/Fe) ratios in the metallicity range from (Fe/H) = − 4.0 up to−3.0 dex (Cayrel et al. 2004, A&A, 416, 1117) is a clear sign that the halo of the Milky Way was well mixed even in the earliest phases of its evolution.