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Session 51 - Interstellar Medium II.
Display session, Thursday, January 08
Exhibit Hall,
The Virginia Tech Spectral Line Imaging Camera (SLIC) uses fast optics in combination with narrowband interference filters and a cryogenic CCD camera to achieve a very high sensitivity to line emission from ionized structures in the interstellar medium. We imaged a large region centered on the Cyg OB2 Association and extending to galactic latitudes \pm 13^\circ, in both the H\alpha line and the [SII] doublet (6717, 6731 Angstroms). The [SII] lines are collisionally excited, whereas H\alpha is produced by recombination following photoionization. We analyzed filament systems on either side of the galactic plane which have been associated with one or more supershells produced by early-type stars in the galactic disk. Our image of the [SII]-to-H\alpha ratio for this region shows large values (typically 0.75) in filament systems on either side of the galactic plane. These results are most readily explained by shock excitation in the filaments, lending support to the idea that these filaments have formed near the peripheries of one or more superbubbles. Closer to the galactic disk and in HII regions, we find lower values for this ratio, for example about 0.2 in the North America Nebula, consistent with models invoking radiative excitation alone. This research was supported by NSF grant AST-9319670 and a grant from the Horton Foundation.
