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Session 50 - Interstellar Medium I.
Display session, Thursday, January 08
Exhibit Hall,
We observed the well-studied reflection nebula IC 63 with the Berkeley spectrograph during the ORFEUS-SPAS 02 mission in November/December 1996. The bandpass extends from 910 to 1216 Åthe spectral resolution is about \lambda/3000. We centered the 26 arcsec field of view on the region previously observed with IUE by Witt et al. (1989), and achieved a total integration time of 3211 sec.
The far ultraviolet spectrum is composed of two components. A continuum is present; its absolute intensity agrees well with the previous measurements in the IUE band. The continuum presumably arises from scattering of starlight by nebular dust and will be discussed in a separate work. The spectrum also reveals emission features whose wavelengths and relative intensities agree well with the molecular hydrogen fluorescence model of Sternberg (1989). The absolute intensity of the H2 fluorescence in the ORFEUS band is about an order of magnitude lower than expected from the fluorescence model and the IUE measurements. We discuss mechanisms to reconcile this discrepancy.
This work was supported by NASA Grant NAG5-696.
