Inhomogeneous Chemical Evolution of the Galactic Halo: Abundance ofr‐Process Elements

We present a stochastic model based on the Monte Carlo technique to study theinhomogeneous chemical evolution of the Galactic halo. In particular, weconsider the local enrichment and subsequent mixing of the interstellar gasresulting from bursts of star formation, following explicitly the fragmentationand coalescence of interstellar gas clouds. The model takes into account themixing of halo gas through cloud-cloud collisions and the delayed mixing ofsupernova ejecta into the interstellar medium. The consequences of the infallof halo gas onto the Galactic disk are also discussed. The mass spectrum ofclouds, the age-metallicity relation, and the G-dwarf distribution areinvestigated at different times. We analyze in detail the predictions of ourmodel for the abundance of elements like Eu, Ba, and Sr in the Galactic halo,following their production by $r$-process nucleosynthesis for differentassumptions on the supernova mass range. Finally, we compare our results withspectroscopic data for the chemical composition of metal-poor halo stars.Comment: Accepted for ApJ, 37 pages, 12 figure