Quantitative near-infrared spectroscopy of Of and WNL stars

From new high signal-to-noise ratio (S/N) 1-2.2 mu m spectroscopy of nine e xtreme early-type stars-including O Iaf, O Iafpe and WN9 types-we determine stellar parameters from detailed atmospheric analysis and evaluate results from near-IR analogues of well-known spectral diagnostics in the optical. We conclude that accurate stellar parameters can be measured from near-IR s pectroscopy alone, an analysis technique important to studies of luminous s tars in the Galactic center and other galaxies. Derived stellar parameters- mass-loss rates, luminosities, surface abundances, temperatures-show good a greement between optical and near-IR analyses, provided that IR data are of sufficient spectral resolution (R > 2000) and S/N (S/N > 30). Wind velocit ies derived from He I 1.0830 mu m are consistent with those from ultraviole t P Cygni profiles. Temperatures 200-1300 K systematically lower are determ ined from the near-IR diagnostics, a difference not significant in determin ing the stellar properties of these objects; which set of spectral lines pr ovides the more accurate physical parameters-optical or IR-cannot at presen t be ascertained. The strength of He I 2.0581 mu m is very sensitive to the extreme ultraviolet energy distribution where line blanketing by heavy ele ments plays an important role; this line should not on its own be considere d a reliable temperature diagnostic. The three peculiar, extreme emission-l ine stars-the O Iafpe stars HD 152386, HD 152408, and HDE 313846-are more s imilar in both morphological and physical characteristics to WNL-type Wolf- Rayet stars than to normal O Iaf supergiants and should be classified as W- R. Their classification should be WN9ha, in which they remain a unique subg roup.