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D.K. Walter (South Carolina State University), P.A. Scowen, J.J Hester, B.D. Moore (Arizona State University), R.J. Dufour, P.M. Hartigan, B. Buckalew (Rice University)
We present the results of our examination of newly acquired images obtained with WFPC-2 of the Bubble Nebula, NGC 7635. These images were taken through narrow-band filters centered on important nebular diagnostic lines, including H alpha, H beta, [O III] at 500.7 nm, [N II] at 658.4 nm, [S II] at 671.7+673.1 nm and the line-free continuum filter F547M. The analysis of the morphology and ionization structure is carried out with an order of magnitude improvement over the best ground-based imagery.
Dense knots embedded in the central cavity show both photoevaporative flow off their surfaces and what appears to be shocked regions which have interacted with the high speed winds (1800-2200 km/s) from the nearby central star, an O6.5IIIf. Their energetic environment is contrasted with high-density knots outside the rim of the bubble which have been photoionized but not shocked. Photoionization modeling of the interior knots is discussed elsewhere in this meeting (see Moore, B.D. et. al). Our HST imagery shows one or more previously undetected, highly ionized structures believed to be inside the wind-blown cavity. These are clearly visible in the high ionization image from [O III], very weak in [N II] and not visible in the low-ionization image of [S II]. Additionally, intricate detail and ionization stratification of the bubble surface and rim are visible. EGGS similar to those found in M16 are also detected in NGC 7635, but which are larger than those in M16 given both the larger angular size and the greater distance to NGC 7635.
Acknowledgements: This work was supported in part by AURA/STScI grant GO-7515. DKW acknowledges additional support from NASA-URC NCC 5-228 and NASA-MUSPIN NCC 5-116.