Are There Any Stars Lacking Neutron-Capture Elements? Evidence from Strontium and Barium

TL;DR

This study investigates whether any halo stars lack detectable neutron-capture elements strontium and barium, finding that these elements are consistently present across various stellar environments, suggesting frequent neutron-capture nucleosynthesis.

Contribution

It provides a comprehensive analysis of stellar abundance data, showing no stars completely lacking neutron-capture elements, thus highlighting the ubiquity of these processes in stellar evolution.

Findings

Strontium and barium are detected in all studied stars.

Upper limits are consistent with the lowest detected ratios.

Neutron-capture elements are nearly always present in halo stars.

Abstract

The cosmic dispersion in the abundances of the heavy elements strontium and barium in halo stars is well known. Strontium and barium are detected in most cool, metal-poor giants, but are these elements always detectable? To identify stars that could be considered probable candidates for lacking these elements, I examine the stellar abundance data available in the literature for 1148 field stars and 226 stars in dwarf galaxies, 776 of which have metallicities lower than [Fe/H]<-2.0. Strontium or barium have been detected in all field, globular cluster, and dwarf galaxy environments studied. All upper limits are consistent with the lowest detected ratios of [Sr/H] and [Ba/H]. The frequent appearance of these elements raises the intriguing prospect that at least one kind of neutron-capture reaction operates as often as the nucleosynthesis mechanisms that produce lighter elements, like magnesium, calcium, or iron, although the yields of heavy elements may be more variable.