Interstellar Iron and Silicon Depletions in Translucent Sight Lines
Sofia, Ulysses J.; Meyer, David M.; Cartledge, Stefan I. B.; Miller, Adam; Lauroesch, J. T.
United States, United Kingdom
Abstract
We report interstellar Fe II and Si II column densities toward six translucent sight lines (AV>~1) observed with the Space Telescope Imaging Spectrograph (STIS). The abundances were determined from the absorption of Si II] at 2335 Å, and several weak Fe transitions including the first reported detections of the λ2234 line. We derive an empirical f-value for the Fe II λ2234 transition of log(fλ)=-1.54+/-0.05. The observed sight lines sample a variety of extinction characteristics as indicated by their RV values, which range from 2.6 to 5.8. The dust-phase abundances of both Si and Fe are positively correlated with the small-grain population (effective radii smaller than a few hundred μm) toward the targets. The physical conditions along the sight lines suggest that this relationship may be due to differences in the survival of small particles in some interstellar environments. The chemical composition of the small grains could either resemble dust mantles or be silicate-rich.
Based on observations with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.