Abundances and Depletions of Neutron-Capture Elements in the Interstellar Medium

TL;DR

This study analyzes the gas-phase abundances and depletion patterns of neutron-capture elements in the interstellar medium using Hubble Space Telescope data and literature, revealing element-specific behaviors and potential intrinsic abundance variations.

Contribution

It provides the first extensive analysis of multiple neutron-capture element depletions in the ISM, including new measurements and a comparison with existing depletion models.

Findings

Ga and Ge depletion patterns align with expectations.

Arsenic shows less depletion and possible supersolar abundance.

Evidence of intrinsic abundance variations for Sn and Pb.

Abstract

We present an extensive analysis of the gas-phase abundances and depletion behaviors of neutron-capture elements in the interstellar medium (ISM). Column densities (or upper limits to the column densities) of Ga II, Ge II, As II, Kr I, Cd II, Sn II, and Pb II are determined for a sample of 69 sight lines with high- and/or medium-resolution archival spectra obtained with the Space Telescope Imaging Spectrograph onboard the Hubble Space Telescope. An additional 59 sight lines with column density measurements reported in the literature are included in our analysis. Parameters that characterize the depletion trends of the elements are derived according to the methodology developed by Jenkins (2009; arXiv:0905.3173). (In an appendix, we present similar depletion results for the light element B.) The depletion patterns exhibited by Ga and Ge comport with expectations based on the depletion results obtained for many other elements. Arsenic exhibits much less depletion than expected, and its abundance in low-depletion sight lines may even be supersolar. We confirm a previous finding by Jenkins (2009; arXiv:0905.3173) that the depletion of Kr increases as the overall depletion level increases from one sight line to another. Cadmium shows no such evidence of increasing depletion. We find a significant amount of scatter in the gas-phase abundances of Sn and Pb. For Sn, at least, the scatter may be evidence of real intrinsic abundance variations due to s-process enrichment combined with inefficient mixing in the ISM.