Possible discovery of the r-process characteristics in the abundances of metal-rich barium stars

TL;DR

This study investigates the abundance patterns of metal-rich barium stars, revealing significant r-process characteristics in some, and suggests their formation involves s-process pollution with possible pre-enrichment effects.

Contribution

It identifies r-process features in metal-rich barium stars and proposes a formation scenario involving s-process pollution and pre-enrichment hypotheses.

Findings

Six barium stars show significant r-process features.

R-rich barium stars resemble metal-poor r-rich and CEMP-r/s stars.

Pre-enrichment may explain abundance patterns better than s-process alone.

Abstract

We study the abundance distributions of a sample of metal-rich barium stars provided by Pereira et al. (2011) to investigate the s- and r-process nucleosynthesis in the metal-rich environment. We compared the theoretical results predicted by a parametric model with the observed abundances of the metal-rich barium stars. We found that six barium stars have a significant r-process characteristic, and we divided the barium stars into two groups: the r-rich barium stars ($C_r>5.0$, [La/Nd]\,$<0$) and normal barium stars. The behavior of the r-rich barium stars seems more like that of the metal-poor r-rich and CEMP-r/s stars. We suggest that the most possible formation mechanism for these stars is the s-process pollution, although their abundance patterns can be fitted very well when the pre-enrichment hypothesis is included. The fact that we can not explain them well using the s-process nucleosynthesis alone may be due to our incomplete knowledge on the production of Nd, Eu, and other relevant elements by the s-process in metal-rich and super metal-rich environments (see details in Pereira et al. 2011).