AAS 197, January 2001
Session 7. Gas in the Galactic ISM
Display, Monday, January 8, 2001, 9:30am-7:00pm, Exhibit Hall

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[7.12] The FUSE Survey of Molecular Hydrogen in Translucent Interstellar Clouds

B.L. Rachford, T.P. Snow, J. Tumlinson, J.M. Shull (U. Colorado), W.P. Blair, S.D. Friedman (JHU), R. Ferlet (Institut d'astrophysique, Paris), E.B. Jenkins (Princeton), D.C. Morton (NRC of Canada), B.D. Savage (U. Wisconsin), A. Vidal-Madjar (Institute d'astrophysique, Paris), D.E. Welty, D.G. York (U. Chicago)

We present preliminary results from the first survey of molecular hydrogen in translucent clouds undertaken with FUSE. Sixteen lines of sight toward early-type stars have been observed, covering a wide range of extinction properties (AV ~ 1--5; RV ~ 2--4). Through profile fitting of the heavily damped low-J lines, and curve-of-growth analysis of the high-J lines, we have determined rotational populations for J = 0 through J = 5, and sometimes as high as J = 7. The total H2 column densities, dominated by J = 0 and J = 1, lie within the range ~3--15 \times 1020 cm-2. The amount of high-J excitation varies considerably from one line of sight to another, reflecting the wide range of UV radiation fields and cloud densities. The ratio N(J=1)/N(J=0) gives kinetic temperatures generally in the range T\rm kin = 50--70 K, similar to the smallest values found for diffuse clouds. We derive hydrogen molecular fractions of ~0.1--0.7, again similar to those found for diffuse clouds with N(H2) \gtrsim 1020 cm-2.

This work is based on data obtained for the Guaranteed Time Team by the NASA-CNES-CSA FUSE mission operated by the Johns Hopkins University. Financial support to U.S. participants has been provided by NASA contract NAS5-32985.

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