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A plasma diagnostic study of two wind-blown shell nebulae: NGC 7635 and NGC 2359

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Title: A plasma diagnostic study of two wind-blown shell nebulae: NGC 7635 and NGC 2359
Author: Jernigan, Tamara Elizabeth
Abstract: We present the first quantitative analysis of the morphology and gaseous-phase properties of two wind-blown shells and their interaction with the interstellar medium by using high spatial resolution emission-line imagery and optical spectrophotometry. We describe the spatially resolved ionization structure and analyze the physical mechanisms responsible for the observed emission by a detailed comparison of emission characteristics with those predicted by both shock-wave and photoionization models. In NGC 7635, our imagery reveals variations in density, temperature, and ionization structure on scales ranging from the size of the nebula (6' x 12') down to the seeing limit of approximately 2.5" (0.03 pc at a distance of 2.6 kpc). The overall emission in the nebula is dominated by the overwhelming contribution of the HII region and is characteristic of photoionization processes. However, when the HII region contribution is removed, the emission in the bubble region is consistent with that produced in the incomplete cooling region behind a stellar-wind shock wave. The embedded, photoevaporating cloud in NGC 7635 contributes enough mass over a dynamical lifetime to account for the shell mass of 5.0 M$\sb{\odot}$. We interpret the "Bubble Nebula" as a blister HII region containing a young stellar-wind bubble formed around a post-main-sequence O star. In NGC 2359, our imagery reveals variations in density, temperature, and ionization structure on scales ranging from the size of the nebula (14' x 14') down to the seeing limit of approximately 2.1" (0.05 pc at a distance of 5.0 kpc). The structure of the HII region can be understood in terms of a photoionized conical cavity protruding into the surrounding molecular cloud. The emission in the bubble region is characteristic of that produced in the incomplete cooling region behind a stellar-wind shock wave. The results of our spectrophotometry reveal an (OIII) temperature of approximately 27,000K for the western rim of the bubble, indicative of shock-excited emission. We interpret NGC 2359 as a blister HII region containing a stellar-wind bubble formed at the edge of a dense, molecular cloud.
Citation: Jernigan, Tamara Elizabeth. (1989) "A plasma diagnostic study of two wind-blown shell nebulae: NGC 7635 and NGC 2359." Doctoral Thesis, Rice University. http://hdl.handle.net/1911/16244.
URI: http://hdl.handle.net/1911/16244
Date: 1989

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