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Session 108 - HII Regions.
Display session, Thursday, January 18
North Banquet Hall, Convention Center
The H \sc ii region N88A is unusual in the metal-poor and relatively dust-free ISM environment of the SMC in that it is heavily reddened and shows a peculiar ionization structure compared to other SMC H \sc ii regions. We report the results of a spectroscopic study of N88A using the following data: HST FOS spectra taken through three apertures using the G130H, G190H, G270H, G400H, and G570H gratings, (2) HST WFPC1 imagery with the F502N and F656N filters, (3) IUE large aperture low and high dispersion SWP and LWR UV spectra, and (4) CTIO 4m longslit spectra taken across the nebula, covering the wavelength range 3650-7450 ÅFrom comparison of IUE spectra of N88A and the ``dust-free" SMC H \sc ii region N81, we found the UV extinction in N88A to be flatter than the SMC law, but similar in having no 2175 Åfeature. A rich emission-line spectrum in the UV and optical wavelengths permit accurate derivations of T_e, N_e, for medium and low ionization zones in the nebula, as well as various ionic abundances in N88A. We also present data on the variations of T_e, N_e, and ionization across the nebula from the CTIO longslit spectra. Elemental abundances are derived both by traditional ICF's and through the use of nebular models. Abundances of He, C, N, O, Ne, Ar, and Si are presented and compared with other SMC nebulae. We find O/H in N88A is similar, while C and N are only marginally higher, suggesting that high dust-to-gas ratio in the ionized volume has not significantly affected the gaseous-phase abundances of these elements. This indicates that most of the dust associated with N88A belongs to the molecular cloud that existed prior to formation of the stars which ionize the H \sc ii region today. However, our \sc HST images indicate a peculiar high ionization ``ring" in the nebula which may be associated with stellar mass loss.
This research was supported in part by grants from AURA/STScI related to GO program 4382, Conacyt(Mexico), and NASA grant NAG5-2677 to Rice University.
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