We study the nucleosynthesis of several neutron capture elements (barium, europium, lanthanum, and yttrium) in local group dwarf spheroidal (dSph) galaxies and in the Milky Way by comparing the evolution of [Ba/Fe], [Eu/Fe], [La/Fe], [Y/Fe], [Ba/Y],
[Ba/Eu], [Y/Eu], and [La/Eu] observed in dSph galaxies and in our Galaxy with predictions of detailed chemical evolution models. The models for all dSph galaxies and for the Milky Way are able to reproduce several observational features of these galaxies, such as a series of abundance ratios and the stellar metallicities distributions. The Milky Way model adopts the two-infall scenario, whereas the most important features of the models for the dSph galaxies are the low star-formation rate and the occurrence of intense galactic winds. We predict that the [s-r/Fe] ratios in dSphs are generally different than the corresponding ratios in the Milky Way, at the same [Fe/H] values. This is interpreted as a consequence of the time-delay model coupled with different star formation histories. In particular, the star-formation is less efficient in dSphs than in our Galaxy and it is influenced by strong galactic winds. Our predictions are in very good agreement with the available observational data. The time-delay model for the galactic chemical enrichment coupled with different histories of star formation in different galaxies allow us to succesfully interpret the observed differences in the abundance ratios of s- and r- process elements, as well as of $alpha$-elements in dSphs and in the Milky Way. These differences strongly suggest that the main stellar populations of these galaxies could not have had a common origin and, consequently, that the progenitors of local dSphs might not be the same objects as the building blocks of our Galaxy.
To study the effects of galactic winds on the stellar metallicity distributions and on the evolution of Draco and Ursa Minor dwarf spheroidal galaxies, we compared the predictions of several chemical evolution models, adopting different prescriptions
for the galactic winds, with the photometrically-derived stellar metallicity distributions of both galaxies. The chemical evolution models for Draco and Ursa Minor, which are able to reproduce several observational features of these two galaxies, such as the several abundance ratios, take up-to-date nucleosynthesis into account for intermediate-mass stars and supernovae of both types, as well as the effect of these objects on the energetics of the systems. For both galaxies, the model that best fits the data contains an intense continuous galactic wind, occurring at a rate proportional to the star formation rate. Models with a wind rate assumed to be proportional only to the supernova rate also reproduce the observed SMD, but do not match the gas mass, whereas the models with no galactic winds fail to reproduce the observed SMDs. In the case of Ursa Minor, the same model as in previous works reproduces the observed distribution very well with no need to modify the main parameters of the model. The model for Draco, on the other hand, is slightly modified. The observed SMD requires a model with a lower supernova type Ia thermalization efficiency ($eta_{SNeIa}$ = 0.5 instead of $eta_{SNeIa}$ = 1.0) in order to delay the galactic wind, whereas all the other parameters are kept the same. The model results, compared to observations, strongly suggest that intense and continuous galactic winds play a very important role in the evolution of local dSphs.
