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D. C. Knauth (Northwestern University), B-G Andersson, S. R. McCandliss, H. W. Moos (The Johns Hopkins University)
Molecular nitrogen (N2) is the most abundant molecule in the Earth's atmosphere and in the less chemically-processed atmosphere of Titan. N2 is also of considerable interest for studies of the interstellar medium because both models of steady-state gas-phase chemistry (Viala 1986) and millimeter wave observations of N2H+ (Womack, Ziurys, & Wyckoff 1992) predict that N2 should be the dominant nitrogen-bearing molecule in interstellar space. Until now, the search for interstellar N2 has been unsuccessful.
We report on Far Ultraviolet Spectroscopic Explorer (FUSE) observations of the first detection of interstellar N2 toward the moderately-reddened star HD 124314 (Knauth et al. 2004). The observed fractional abundance of N2/H2 = 3.3 \times 10-7 is almost two orders of magnitude larger than expected from models of interstellar nitrogen chemistry for diffuse clouds, but is also less than expected from dark cloud chemistry predictions. In addition, we present preliminary analysis of high signal-to-noise data on 20 Aql yields x(N2) \leq 4.7 \times 10-8, which is surprisingly low given that 20 Aql has a factor-of-4 higher CN abundance. There appears to be an anti-correlation between N2 and CN: Is this anti-correlation caused by differences in the predictions of diffuse and dark cloud chemistry? Further observations of interstellar N2 are required to fully understand the implications for interstellar nitrogen chemistry.
This work is based on data obtained for the Guaranteed Time Team by the NASA-CNES-CSA FUSE mission. Financial support has been provided by NASA contract NAS5-32985.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.