AAS 202nd Meeting, May 2003
Session 29 Molecular Clouds and the ISM
Poster, Tuesday, May 27, 2003, 10:00am-6:30pm, West Exhbit Hall

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[29.10] FUSE Observations of Interstellar CO and H2 toward Stars in Cepheus

Y. Sheffer, S.R. Federman (U. Toledo)

Far ultraviolet spectra contain numerous electronic transitions of CO and H2. In the course of analyzing FUSE data on O and B stars in the Cep OB2 and OB3 Associations, we detected absorption features from Rydberg bands of CO. While the B-X (0-0), C-X (0-0), and E-X (0-0) bands have been observed before with Copernicus and ORFEUS, a larger number of higher-energy (shorter-wavelength) bands is observed for the first time. Absorption in these higher-energy bands leads to CO photodissociation. Thus, it is important to measure their oscillator strengths, which are key ingredients in theoretical modeling of CO photochemistry in interstellar environments. Our results confirm that previous lab measurements underestimated the f-values of these bands. Comparison with our recent lab measurements taken at the LURE-SuperACO Synchrotron in Orsay, France, will be made.

The premier molecule in the interstellar medium, H2, has to be modeled and divided out in order to reveal weaker absorption features in FUSE spectra. We also compare H2 results with optical observations of CH along the same lines of sight. While it has been known that H2 and CH abundances track each other very well, we find that the slope of the correlation can actually vary from one OB association to another. Clearly, the local chemistry of these molecules is affected by physical conditions and radiation field characteristics that have unique combinations in different environments.

This work was supported by NASA grants NAG5-4957, NAG5-8961, and NAG5-10305.

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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.