Galactic evolution of rapid neutron capture process abundances: the
  inhomogeneous approach
  For the origin of heavy r-process elements, different sources have been
proposed, e.g., core-collapse supernovae or neutron star mergers. Old
metal-poor stars carry the signature of the astrophysical source(s). Among the
elements dominantly made by the r-process, europium (Eu) is relatively easy to
observe. In this work we simulate the evolution of europium in our galaxy with
the inhomogeneous chemical evolution model 'ICE', and compare our results with
spectroscopic observations. We test the most important parameters affecting the
chemical evolution of Eu: (a) for neutron star mergers the coalescence time
scale of the merger ($t_{\mathrm{coal}}$) and the probability to experience a
neutron star merger event after two supernova explosions occurred and formed a
double neutron star system ($P_{\mathrm{NSM}}$) and (b) for the sub-class of
magneto-rotationally driven supernovae ("Jet-SNe"), their occurrence rate
compared to standard supernovae ($P_{\mathrm{Jet-SN}}$). We find that 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
inhomogeneous models agrees with observations and whether this provides
constraints on supernova explosion models and their nucleosynthesis.
