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