Using neutron-capture abundances as a tracer of Galactic halo formation

Abstract

Chemical differences in stellar populations are one method to study the formation and evolution of the Galactic halo of the Milky Way. In particular, there are low α-element stars and high αelement stars in the Galactic halo that also show differences in their neutron-capture elemental abundances. Asymptotic giant branch (AGB) stars are an important source of neutron-capture elements that are produced via the slow (s-) neutron-capture process. To better understand these abundance differences, models of AGB stars have been calculated at a metallicity of Z = 0.001 ([Fe/H] ≈−1.2). We present theoretical abundance predictions of H through to Pb from low-mass AGB stars spanning a mass range of 1M to 3M . We compare the abundance distribution of the 1.5M stellar model to that of Cristallo et al. (2011) and find that they are in good agreement. Finally, we compare final surface abundances from stellar models of 1M and 3M , Z = 0.001 that have been computed using two different nuclear networks. We find small abundance differences in the s-process peaks for the 1M but no differences in the neutron-capture elements for the 3M model.