AAS 199th meeting, Washington, DC, January 2002
Session 11. Interstellar Medium - I
Display, Monday, January 7, 2002, 9:20am-6:30pm, Exhibit Hall

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[11.10] Physical conditions of the molecular cloud toward HD 37903

D.H. Lee (Satellite Technology Research Center, Korea Advanced Institute of Science and Technology (KAIST)), K.W. Min, S.J. Hong (Dept. of Physics, KAIST), K.S. Ryu (Satellite Technology Research Center, KAIST), M. Hurwitz (Space Science Lab., U. C. Berkeley)

We analyze the H2 and CO absorption transitions along the line of sight towards HD 37903 over the 1045-1060 and 1086-1102 Åwavelength regions, which is observed by Berkeley Extreme and Far-ultraviolet Spectrometer (BEFS) on the ORFEUS II telescope. HD 37903 is a bright UV emitting star embedded in the southern part of the Orion B molecular cloud, illuminating the reflection nebula NGC 2023. Based on the theory of formation and dissociation of molecular hydrogen in the Far-UV spectral range (Jura 1975), we address the physical conditions of the foreground gas toward HD 37903, such as the density n, temperature T, and the UV intensity IUV, by analyzing the H2 absorption lines of J = 0-5 rotational levels. The observed gas is shown to surround the photodissociation region of the NGC 2023. We identify the CO absorption line at 1088 Åand calculate the direct abundance ratio [CO]/[H2] to be 4.6 x 10-7, which is consistent with the survey study made by Federman et al. (1980).

Jura 1975, ApJ, 197, 581

Federman et al. 1980, ApJ, 242, 545

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