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The Voyager Ultraviolet Spectrometer (UVS) data on O and B stars has proven to be valuable in the study of interstellar extinction. This region of the spectrum is particularly interesting because dust opacity is much higher in the UV wavelengths than in the visible or IR. In this work, we estimate the abundance of molecular hydrogen by combining known extinction curves with stellar atmosphere models.
In Snow, Allen \& Polidan (1990, ApJ, 359, L27), we derived extinction curves by comparing reddened and unreddened stars of like spectral type. In that work, the spectra were first corrected for known amounts of H$_2$ absorption. High column densities of H$_2$ appear as a series of absorption lines below 1150 \AA\ which, at Voyager resolution, mimics the effect of additional dust absorption. The current study uses known extinction and model spectra to estimate the column density of H$_2$ along several lines of sight. We do this by first selecting an extinction curve to de-redden the star and then finding the column density of H$_2$ which gives the best match to the appropriate Kurucz model spectrum. This is an iterative process which selects the best combination of extinction curve and H$_2$ column density that matches the model stellar spectrum.
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