The origin of elements made by the rapid neutron-capture process (r-process) is not fully understood. Different sources have been proposed, e.g., core-collapse supernovae and neutron star mergers. Old metal-poor stars carry the signature of the astrophysical r-process source(s). Europium is the most indicative element to trace the r-process production, since it is mostly made by the r-process and it is easy to observe compared to other heavy r-process elements. In this work we simulate the evolution of europium in our Galaxy with the inhomogeneous chemical evolution model ICE, and we compare our results with spectroscopic observations. We test the most important parameters affecting the chemical evolution of the r-process element Eu: (a) for neutron star mergers the coalescence time scale of the merger and the probability to experience a neutron star merger event after two supernova explosions occurred and formed a double neutron star system ) and (b) for the sub-class of magneto-rotationally driven Supernovae (Jet-SNe, their occurrence rate compared to standard supernovae ). The main results can be summarized as follows. The observed [Eu/Fe] pattern in the galaxy can be reproduced by a combination of neutron star mergers and magneto-rotationally driven supernovae as r-process sources, while neutron star mergers alone seem to set in at too high metallicities. Jet-SNe provide a cure for this deficiency at low metallicities. Furthermore, we confirm that local inhomogeneities can explain the observed large spread in the europium abundances at low metallicities. We also predict the evolution of [O/Fe] to test whether the spread in alpha-elements for in- homogeneous models agrees with observations and whether this provides constraints on supernova explosion models and their nucleosynthesis.
B. Wehmeyer, M. Pignatari and F. Thielemann
Mon, 2 Feb 15