Interstellar O2. II. VUV oscillator strengths of Schumann-Runge lines and prospects for space telescope observations

Interstellar molecular oxygen should be detectable in interstellar clouds through observations of its absorption lines in the spectra of background stars. This paper describes and presents the results of measurements of oscillator strengths for some lines in the vacuum ultraviolet (VUV) spectrum of O2. Lines of the (13,0) through (16,0) bands of the B 3Σ-/sub u/-X3Σ-/sub g/, Schumann-Runge system between 1760 A and 1790 A will be the most suitable for searches for absorption by interstellar O2 with the High Resolution Spectrograph on Space Telescope. The strongest lines in these bands have oscillator strengths of about 3 x 10-5. The strongest interstellar cloud absorption features will be lines with froughly-equal 1.5 x 10-5 that will have equivalent widths of about 13 mA in dark interstellar clouds with O2 column densities of 1017 cm-2, such as that in front of HD 29647