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Session 108 - HII Regions.
Display session, Thursday, January 18
North Banquet Hall, Convention Center
We present new long-slit spectroscopy and narrow-band CCD imaging of the peculiar H II region N44C in the Large Magellanic Cloud, which exhibits strong He II recombination emission, although the apparent ionizing star is of spectral class O. The spectra cover the range 3300-7400 Åincluding the emission lines [Ne V] 3426 Å\ and [Ar V] 7005 Å\, which provide important constraints on the stellar radiation field. We use the emission line spectrum of N44C to constrain the stellar ionizing continuum and to estimate the element abundances for He, O, N, Ne, S, and Ar in the nebula, to compare with normal LMC H II regions. The helium and oxygen abundances in N44C appear to be normal compared to other well-studied H II regions in the LMC. N/O appears somewhat high (N^+/O^+ = 0.05 \pm 0.04), but the value is uncertain because of the weak [N II] measurement and the very large correction for unseen higher ionization states of nitrogen. The spectral type of the O star is uncertain because of severe contamination by nebular emission, but is in the range O3-O7. We also set significant upper limits on the amounts of Ne^+4 and Ar^+4 in N44C, which places severe constraints on the number of ionizing photons above 60 eV from the star. The observed ionization will be compared with results from photoionization models using hot stellar atmospheres.
Program listing for Thursday