The Abundance of Interstellar Nitrogen

Using the HST Goddard High Resolution Spectrograph (GHRS), we have obtained high S/N echelle observations of the weak interstellar N I 1160,1161 absorption doublet toward the stars Cas, Ori, Ori, Ori, Sco and Sco. In combination with a previous GHRS measurement of N I toward Oph, these new observations yield a mean interstellar gas-phase nitrogen abundance (per 10 H atoms) of 10 N/H = 75 4 ( 1 ). There are no statistically signi cant variations in the measured N abundances from sightline to sightline and no evidence of density-dependent nitrogen depletion from the gas phase. Since N is not expected to be depleted much into dust grains in these di use sightlines, its gas-phase abundance should re ect the total interstellar abundance. Consequently, the GHRS observations imply that the abundance of interstellar nitrogen (gas plus grains) in the local Milky Way is about 80% of the solar system value of 10 N/H = 93 16. Although this interstellar abundance de cit is somewhat less than that recently found for oxygen and krypton with GHRS, the solar N abundance and the N I oscillator strengths are too uncertain to de nitively rule out either a solar ISM N abundance or a 2/3 solar ISM N abundance similar to that of O and Kr. Subject headings: ISM: abundances | ISM: atoms