Oscillator strengths for transitions in N I and the interstellar abundance of nitrogen

Oscillator strengths based on configuration interaction wavefunctions are presented for both optically allowed and forbidden transitions in N I. Particular attention is given to the multiplets at 951 Å (2p3 4S−2p23d2D), 952 Å (2p3 4S−2p23d4D) and 1160 Å (2p3 4S−2p23s2P) which have been extensively observed by the COPERNICUS satellite. For these transitions, the radiative rates are estimated to have an accuracy of 20 per cent or better. A re-analysis of the COPERNICUS observational data indicates there is no depletion of nitrogen towards reddened stars. Possible causes of a small depletion (⋍0.2 dex) towards several nearby unreddened stars are discussed.