AAS 201st Meeting, January, 2003
Session 77. The Interstellar Medium II
Poster, Wednesday, January 8, 2003, 9:20am-6:30pm, Exhibit Hall AB

[Previous] | [Session 77] | [Next]

[77.11] On the Potential Variation of the Interstellar N/O Ratio

D. C. Knauth, B-G Andersson, H. W. Moos (Center for Astrophysical Sciences, The Johns Hopkins University)

To date, all studies of interstellar O~{\small I} support a constant O/H abundance (e.g., Meyer, Jura, & Cardelli 1998, ApJ, 493, 222). For interstellar N~{\small I}, the situation is not as well determined. Meyer, Cardelli, & Sofia (1997, ApJ, 490, L103) show a relatively constant N~{\small I} abundance utilizing seven high-quality GHRS measurements of the weak N~{\small I} \lambda1160 doublet. In striking contrast, factor-of-2 variations in the N~{\small I} abundance have been detected using high quality IMAPS data (e.g., Jenkins et al. 1999, ApJ, 520, 182; Sonneborn et al. 2000, ApJ, 545, 277). Additionally, recent work (Moos et al. 2002, ApJS, 140, 3 and references therein) shows large scatter when the N/O ratio is considered for 7 lines of sight in the local interstellar medium.

Nitrogen is primarily formed during the CNO cycle and expelled into the ISM through the massive winds of Asymptotic Giant Branch (AGB) stars, while O is formed during helium shell burning and returned to the ISM through supernovae. Therefore, the N/O ratio and its possible variation have implications for mixing processes in the interstellar medium (ISM). We present high signal-to-noise (S/N \geq 50) Far-Ultraviolet Spectroscopic Explorer (FUSE) observations on the weak interstellar N~{\small I} \lambda1160 doublet toward stars that have existing high quality O~{\small I} measurements. Our preliminary results when combined with the existing high quality N~{\small I} and O~{\small I} data will probe the extent of potential N/O variations.

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.

[Previous] | [Session 77] | [Next]

Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.