Abstract
We obtained nebular spectroscopy of LMC H II regions having classified stellar populations, thereby strongly constraining the ionization input parameters. Using photoionization models, we then evaluate the performance of nebular diagnostics of T[ scriptstyle star ]and abundance. We introduce [Ne III]/H beta as a nebular diagnostic of the ionizing stellar T[ scriptstyle star ]. In contrast to the widely-used ensuremath {eta ^prime } parameter, [Ne III]/H beta has greater sensitivity to mid and early O-stars, and is robust to nebular morphology and the presence of shocks. We present a preliminary calibration of both T[ scriptstyle star ]diagnostics for LMC metallicity. We also introduce S[234] equiv ([S II] + [S III] + [S IV])/H beta as a diagnostic of S abundance. S[234] is much less sensitive to the nebular ionization parameter than is S[23] or R[23]. The intensity of [S IV]10.5 mu m is easily estimated from the optical and near-IR line ratios. We present calibrations of S[23] and S[234] that are reliable at metallicities Z ≲ 0.5Z[ scriptstyle sun ].
