Abstract

In this paper we review the current ideas about the formation of our Galaxy. In particular, the main ingredients necessary to build chemical evolution models (star formation, initial mass function and stellar yields) are described and discussed. A critical discussion about the main observational constraints available is also presented. Finally, our model predictions concerning the evolution of the abundances of several chemical elements (H, D, He, C, N, O, Ne, Mg, Si, Ca and Fe) are compared with observations relative to the solar neighborhood and the whole disk. We show that from this comparison we can constrain the history of the formation and evolution of the Milky Way as well as the nucleosynthesis theories concerning the Big Bang and the stars.

Highlights

  • Elements with Z >30 are labelled neutron capture elements: they are manly formed through neutron captures, and not through fusion, this process beyond iron (Z=26) being endothermic

  • We start by analyzing the results of the r-model, which assumes only the contribution from massive stars via our empirical r-process yields

  • As the Sr yields adopted here are obtained just by using the Ba/Sr ratio matching the observed solar system r-process [19], this ratio is constant with metallicity. This suggests that the some other physical process, taking place in the same mass range of what we have called extended r-process might be contributing to produce part of the Sr and Ba in the very early Universe

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Summary

Introduction

Elements with Z >30 are labelled neutron capture elements: they are manly formed through neutron captures, and not through fusion, this process beyond iron (Z=26) being endothermic. In the case of neutron capture elements the situation is more complex due to the presence of a huge spread in the observed abundance ratios of the EMP stars, recently confirmed by the results of [11] An explanation for these inhomogeneities relies on the stochastic formation of massive stars [12]. The spread is generated by the enrichment of different species if they are produced by different ranges of masses, providing a finite length of the mixing zone This has been shown for heavy neutron capture elements vs iron in the inhomogeneous chemical evolution model by [12]; the same approach has been used for CNO (see [13]) to investigate the implications of the inhomogeneous modeling in the observed spread (in particular of the ratio N/O) in EMP stars. It follows that for the spread between the light and the heavy neutron capture elements we should investigate this model and so in this paper we use this scenario to analyze the impact of the new results for s-process in massive stars boosted by fast rotation [6]

Observational data
The chemical evolution models
Empirical yields for the r-process
The contribution of spinstars
Results
Discussions and conclusions
Full Text
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