Is There Enhanced Depletion of Gas‐Phase Nitrogen in Moderately Reddened Lines of Sight?

We report on the abundance of interstellar neutral nitrogen (NI) for 30sightlines, using data from the Far Ultraviolet Spectroscopic Explorer (FUSE)and the Hubble Space Telescope (HST). NI column densities are derived bymeasuring the equivalent widths of several ultraviolet absorption lines andsubsequently fitting those to a curve of growth. We find a mean interstellarN/H of 51+/-4 ppm. This is below the mean found by Meyer et al. of 62(+4,-3)ppm (adjusted for a difference in f-values). Our mean N/H is similar, however,to the (f-value adjusted) mean of 51+/-3 ppm found by Knauth et al. for alarger sample of sightlines with larger hydrogen column densities comparable tothose in this study. We discuss the question of whether or not nitrogen showsincreased gas-phase depletion in lines of sight with column densitieslog(H_tot) >~ 21, as claimed by Knauth et al. The nitrogen abundance in theline of sight toward HD 152236 is particularly interesting. We derive verysmall N/H and N/O ratios for this line of sight that may support a previoussuggestion that members of the Sco OB1 association formed from an N-deficientregion.Comment: Accepted in The Astrophysical Journal, 9/2006 (expected pub. date: 1/2007) 38 pages, 5 figures (4 color