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K. France, S. R. McCandliss, B-G Andersson, P. D. Feldman (JHU)
We present far-ultraviolet spectroscopy of the photodissociation region IC 63. These observations mark the first time that the entire electronic transition band of H2 has been studied as a whole and the first look at the resolved rotational structure of molecular hydrogen below 1200 A in IC 63. Models of molecular hydrogen fluorescence in IC 63 have overpredicted the absolute flux at short wavelengths by as much as an order of magnitude. We present a fluorescence model that resolves the discrepancies between mid and far-ultraviolet emission by employing two temperature components, self-absorption out of the ground vibrational level of H2, and a flux calibrated input spectrum of the exciting source, gamma-Cas (HD 5394). A scattered light spectrum of gamma-Cas obtained by the Far Ultraviolet Spectroscopic Explorer (FUSE) at an angular separation of ~1' has been flux calibrated using the results of a recent sounding rocket flight to observe gamma-Cas with a far-ultraviolet sensitive CCD. The spectrum of IC 63 acquired with the Hopkins Ultraviolet Telescope allows us to test this model with spectral coverage across the entire 900-1650 A window spanned by fluorescent H2 emission. This model can be tested in finer detail by a comparison with high-resolution spectra of IC 63 from FUSE. Our model finds relatively good agreement with the observed emission line strengths seen in the spectra.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.