AAS 201st Meeting, January, 2003
Session 47. The Interstellar Medium I
Poster, Tuesday, January 7, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[47.09U] Detection of the H- ion in the ISM with FUSE

M.K. Andre, J.M. Désert (Institut d'Astrophysique de Paris), D. Ehrenreich (Johns Hopkins University), R. Ferlet, G. Hébrard, S. Lacour (Institut d'Astrophysique de Paris), F. LePetit (Observatoire de Paris-Meudon), V. Leboutei (Institut d'Astrophysique de Paris), C. Oliveira, P. Sonnentrucker (Johns Hopkins University)

We use far-UV spectra obtained with FUSE toward distant early B and late O type stars to attempt the first detection of the H- ion in the ISM. The photodetachment cross sections of the H- shows pronounced resonances corresponding to the doubly excited 1P state at 1132.08 Åand 1134.94 Å. The presence of the N I triplet and one Fe II line in the same region makes it mandatory to produce a detailed model of the ISM (with higher resolution STIS data when available) in order to deblend the 1134.94 Å line.

In the early Universe, the two steps gas phase reaction (1) H+e-=H-+hw, (2) H+H-=H2+e- is recognized to be an important source of H2. However, the radiation association of an electron with an H atom via reaction (1) is a very slow process and it is believed that in the current ISM catalysis of the H2 on the surface of dust is a much more efficient way. Yet, in a recent paper, Field (2000) argues that H- might be efficiently formed on the surface of the grains as well. If such is the case, chemical models of the ISM may be lacking an important and non negligible source for the H2 molecules. Our observations of H- will help to put stringent limits on this scenario or make a definitive statement.

This work has made use of the FUSE database maintained at the Institut d'Astrophysique de Paris (http:\\fuse.iap.fr).

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