AAS 199th meeting, Washington, DC, January 2002
Session 97. Interstellar Medium - III
Display, Wednesday, January 9, 2002, 9:20am-6:30pm, Exhibit Hall

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[97.02] ORFEUS observations of the interstellar CO abundance ratio

K.W. Min (Dept. of Physics, Korea Advanced Institute of Science and Technology), D.H. Lee, K.S. Ryu (Satellite Technology Research Center, Korea Advanced Institute of Science and Technology), S.J. Hong, J.H. Shin (Dept. of Physics, Korea Advanced Institute of Science and Technology), W.Y. Han, U.W. Nam, K.I. Seon, J.H. Park, I.S. Yuk, H. Jin (Korea Astronomy Observatory), M. Hurwitz (Space Sciences Lab., U. C. Berkeley)

We present a survey result of interstellar CO absorption lines in the C-X 1088 Åband toward 52 early-type stars made with the Berkeley Extreme and Far-ultraviolet Spectrometer (BEFS) on the ORFEUS telescope in 1993 and 1996. While the previous survey by Copernicus (Federman et al. 1980) was restricted to the disk stars near the Sun, ORFEUS targets are extended to the halo stars, and even to the LMC's. We set the CO excited temperature to be 4 K to fit the synthesis of the CO bands and obtain the b-value of 1 km s-1 through \chi2 minimization. CO column densities are derived in 16 directions and CO/H2 abundance ratios are calculated for each of them with the H2 column density obtained from the same BEFS data. The abundance ratios are consistent with those of Federman et al. (1980). We compare the physical conditions between the halo stars and the disk stars, and discuss the UV radiation density effects on the abundance ratios.

Federman et al. 1980, ApJ, 242, 545

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