Absolute Vacuum Ultraviolet Oscillator Strengths in CO II and the Interstellar Cobalt Abundance

Abstract

We report the first laboratory measurements of 10 absolute oscillator strengths (f-values) for vacuum ultraviolet lines of Co II. The oscillator strengths are measured with the High-Sensitivity Absorption Spectroscopy Experiment at the University of Wisconsin. The measurements serve as a test of theoretical work on Co II f-values and set an absolute scale for relative oscillator strengths from spectra taken with the Hubble Space Telescope. Observations of interstellar absorption in the direction of ρ Oph A result in the determination of the f-value for an additional line. The set of absolute f-values is used to derive the interstellar abundance of cobalt toward ρ Oph A and ζ Oph. Cobalt is found to be less severely depleted onto grains than earlier analyses based on available theoretical f-values suggested. As a consequence of this revision, the correspondence between depletion and condensation temperature is somewhat weakened.

Based on observations obtained with the NASA/ESA Hubble Space Telescope through the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.