Rubidium in the Interstellar Medium

TL;DR

This study measures interstellar rubidium isotope ratios toward multiple stars, revealing variations from the solar system value and suggesting isotope enrichment processes in certain molecular cloud regions.

Contribution

It provides new interstellar rubidium isotope measurements and compares them to solar system ratios, offering insights into nucleosynthesis in different interstellar environments.

Findings

Most sight lines match the solar Rb isotope ratio within uncertainties.

HD 147889 shows a significantly lower Rb isotope ratio, indicating isotope enrichment.

Interstellar Rb/K ratio is lower than meteoritic values across all observed lines of sight.

Abstract

We present observations of interstellar rubidium toward o Per, zeta Per, AE Aur, HD 147889, chi Oph, zeta Oph, and 20 Aql. Theory suggests that stable 85Rb and long-lived 87Rb are produced predominantly by high-mass stars, through a combination of the weak s- and r-processes. The 85Rb/87Rb ratio was determined from measurements of the Rb I line at 7800 angstroms and was compared to the solar system meteoritic ratio of 2.59. Within 1-sigma uncertainties all directions except HD 147889 have Rb isotope ratios consistent with the solar system value. The ratio toward HD 147889 is much lower than the meteoritic value and similar to that toward rho Oph A (Federman et al. 2004); both lines of sight probe the Rho Ophiuchus Molecular Cloud. The earlier result was attributed to a deficit of r-processed 85Rb. Our larger sample suggests instead that 87Rb is enhanced in these two lines of sight. When the total elemental abundance of Rb is compared to the K elemental abundance, the interstellar Rb/K ratio is significantly lower than the meteoritic ratio for all the sight lines in this study. Available interstellar samples for other s- and r- process elements are used to help interpret these results.