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B. Buckalew, R. Dufour, P. Ghavamian, P. Hartigan (Rice U.), D. Walter (SCSU), J. Hester, P. Scowen (ASU)
We report the results of longslit spectroscopy of the wind-blown bubble and photoevaporating knots around the O6.5{\sc iii}f star BD+ 60\circ2522 made with the Space Telescope Imaging Spectrograph. The Of star is the primary ionizing source for the H~{\sc ii} region NGC 7635, located in the Perseus Arm. The spectra were taken through a 0.2'' \times 52'' slit with low and medium resolution gratings covering the wavelength range 2900-6870 Å. Observations with two slit orientations were made; one across the line of embedded knots to the west of the Of star and the second running from the Of star across the bubble to the NE. The 2D STIS spectra permit us to subtract the surrounding H~{\sc ii} region's diffuse emission from that of the knots and the bubble, and to study the spatial variations in various emission lines in these features to a resolution of \approx~0.1'', an order of magnitude improvement over the best ground-based spectra of this object in the literature. We present high spatial resolution emission line and line ratio profiles across the bubble and knots, and compare them with the predicted variations from photoionization, photoevaporation, and wind-shock models. We also present an analysis of temperatures, densities, and abundances in the features from higher S/N spectra extracted over selected lengths of the slit.
From our analysis, we find that our measured abundances for nitrogen and oxygen are what we would expect for an H~{\sc ii} region at this galactocentric distance. However, the rim helium and carbon abundances show an enhancement which may be caused by contamination from the stellar wind. From our spatial scan studies of the knots and rim, we conclude that the knots are composed of photoevaporating knots surrounded by an ionization front, confirming the results of the imagery which indicate that the knots are like the EGGs of M16 seen face on. The rim appears to be the edge of a slightly supersonic shell of ionized gas that is being snowplowed through the surrounding H~{\sc ii} region by the star's supersonic wind.
Acknowledgements. This research was supported in part by AURA/STScI grant GO-7515 and NASA-Ames grant NGT 2-52252.
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