Element Abundance Patterns of Metal-Poor Halo Stars

Abstract

We describe a stochastic halo formation model to compute the early chemical enrichment of the interstellar medium (ISM) of the halo. Local inhomogeneities caused by single supernovae lead to different element abundance patterns in very metal-poor stars. These can be seen as scatter in the abundance ratios of metal-poor halo stars. The early chemical evolution of the halo proceeds in different enrichment phases: At first, the halo ISM is unmixed and dominated by local inhomogeneities. The mixing then gradually increases, leading finally to a chemically homogeneous ISM with an IMF averaged element abundance pattern. For some elements (Si, Ca), the scatter in the element-to-iron ratio [El/Fe] of metal-poor halo stars can be reproduced. Stellar yields of other elements predict a scatter which is too large (O, Mg) or too small (Ni). This result does not depend on the details of the galactic model but is solely determined by theoretical SN yields. This demonstrates the need for revised, self-consistent nucleosynthesis models. A more detailed discussion of the model and its results can be found in Argast et al. (2000).