CS29497-030 Abundance Constraints on Neutron-Capture Nucleosynthesis

Abstract

Chemical abundances and upper limits of three dozen elements have been derived for the binary blue metal-poor, extremely lead-rich star CS29497-030. The findings include a large contribution of s-process material (e.g., [Pb/Fe] >3.5) and a large contribution of r-process material (e.g, [Eu/Fe] ∼2), abundances which place it in the class of objects known as r+s stars. The ratio of [Zr/Nb] ∼0, along with its stellar parameters, indicates that it is not an intrinsic AGB star. Modelling the abundance distribution (which includes the first Bi abundance determination for any metal-poor star) with s-process calculations employing FRANEC models, there is excellent agreement with the observations by adopting a 1.3 M_{[odot ]} AGB model with an enhanced ¹³C-pocket and a pre-enrichment of r-process material. In this scenario, the initial abundances of CS29497-030 and its binary partner arose from a parent cloud with an extreme r-process abundance, in which star formation was triggered by a core-collapse supernova which polluted, snowplowed, and clumped a nearby molecular cloud. Pollution from the former AGB star's dredged-up material subsequently enriched the envelope composition of CS29497-030 (Ivans et al. 2005). Critical tests of this model and scenario include the dependence of abundance ratios on systematics due to non-LTE effects, the choice of stellar parameters and model atmospheres, and the assumed abundance pattern of the protostellar cloud out of which the CS29497-030 binary system formed.