Is there enhanced depletion of gas-phase nitrogen in moderately reddened lines of sight?
JENSEN A.G., RACHFORD B.L. and SNOW T.P.
Abstract (from CDS):
We report on the abundance of interstellar neutral nitrogen (N I) for 30 sight lines, using data from the Far Ultraviolet Spectroscopic Explorer (FUSE) and the Hubble Space Telescope (HST). N I column densities are derived by measuring the equivalent widths of several ultraviolet absorption lines and subsequently fitting those to a curve of growth. We find a mean interstellar N/H of 51±4 ppm. This is below the mean found by Meyer et al. of 62+4–3ppm (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 a larger sample of sight lines with larger hydrogen column densities comparable to those in this study. We discuss the question of whether or not nitrogen shows increased gas-phase depletion in lines of sight with column densities logN(Htot)≳21, as claimed by Knauth et al. The nitrogen abundance in the line of sight toward HD 152236 is particularly interesting. We derive very small N/H and N/O ratios for this line of sight that may support a previous suggestion that members of the Sco OB1 association formed from an N-deficient region.
ISM: Abundances - Ultraviolet: ISM