Galactic evolution of rapid neutron capture process abundances: the inhomogeneous approach

Abstract

For the origin of heavy r-process elements, different sources have been\nproposed, e.g., core-collapse supernovae or neutron star mergers. Old\nmetal-poor stars carry the signature of the astrophysical source(s). Among the\nelements dominantly made by the r-process, europium (Eu) is relatively easy to\nobserve. In this work we simulate the evolution of europium in our galaxy with\nthe inhomogeneous chemical evolution model 'ICE', and compare our results with\nspectroscopic observations. We test the most important parameters affecting the\nchemical evolution of Eu: (a) for neutron star mergers the coalescence time\nscale of the merger ($t_{\\mathrm{coal}}$) and the probability to experience a\nneutron star merger event after two supernova explosions occurred and formed a\ndouble neutron star system ($P_{\\mathrm{NSM}}$) and (b) for the sub-class of\nmagneto-rotationally driven supernovae ("Jet-SNe"), their occurrence rate\ncompared to standard supernovae ($P_{\\mathrm{Jet-SN}}$). We find that the\nobserved [Eu/Fe] pattern in the galaxy can be reproduced by a combination of\nneutron star mergers and magneto-rotationally driven supernovae as r-process\nsources. While neutron star mergers alone seem to set in at too high\nmetallicities, Jet-SNe provide a cure for this deficiency at low metallicities.\nFurthermore, we confirm that local inhomogeneities can explain the observed\nlarge spread in the europium abundances at low metallicities. We also predict\nthe evolution of [O/Fe] to test whether the spread in $\\alpha$-elements for\ninhomogeneous models agrees with observations and whether this provides\nconstraints on supernova explosion models and their nucleosynthesis.\n