Interstellar Iron and Silicon Depletions in Translucent Sight Lines

Abstract

We report interstellar FeII and SiII column densities toward six translucent sight lines (A_V >~ 1) observed with the Space Telescope Imaging Spectrograph (STIS). The abundances were determined from the absorption of SiII] at 2335 Angstroms, and several weak Fe transitions including the first reported detections of the 2234 Angstrom line. We derive an empirical f-value for the FeII 2234 Angstrom transition of log(f lambda) = -1.54 +/- 0.05. The observed sight lines sample a variety of extinction characteristics as indicated by their R_V values, which range from 2.6 - 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 micron) 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.

accepted for publication in ApJ

References in corpus (4)

• Ultraviolet Extinction Properties in the Milky Way
• The Homogeneity of Interstellar Oxygen in the Galactic Disk
• The Absorption Spectrum of High-Density Stellar Ejecta in the Line-of-Sight to Eta Carinae
• FUSE Measurements of Far Ultraviolet Extinction. I. Galactic Sight Lines

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