The interstellar N2 abundance towards HD 124314 from far-ultraviolet observations

• Published in: Nature (London) 2004-06, Vol.429 (6992), p.636-638
• Main Authors: Knauth, David C., Andersson, B-G, McCandliss, Stephan R., Warren Moos, H.
• Format: Article
• Language: English
• Subjects: Astronomy; Characteristics and properties of the milky way; Chemical composition and chemical evolution; Earth, ocean, space; Exact sciences and technology; Humanities and Social Sciences; letter; Molecules; multidisciplinary; Nitrogen; Science; Science (multidisciplinary); Stellar systems. Galactic and extragalactic objects and systems. The universe; Wavelengths
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature02614

The abundance of interstellar molecular nitrogen (N 2 ) is of considerable importance: models of steady-state gas-phase interstellar chemistry 1 , 2 , together with millimetre-wavelength observations 3 , 4 of interstellar N 2 H + in dense molecular clouds predict that N 2 should be the most abundant nitrogen-bearing molecule in the interstellar medium. Previous attempts to detect N 2 absorption in the far-ultraviolet 5 or infrared 6 (ice features) have hitherto been unsuccessful. Here we report the detection of interstellar N 2 at far-ultraviolet wavelengths towards the moderately reddened star HD 124314 in the constellation of Centaurus. The N 2 column density is larger than expected from models of diffuse clouds and significantly smaller than expected for dense molecular clouds 1 . Moreover, the N 2 abundance does not explain the observed variations 7 in the abundance of atomic nitrogen (N I) towards high-column-density sightlines, implying that the models of nitrogen chemistry in the interstellar medium are incomplete 8 .