Quantitative Near‐Infrared Spectroscopy of Of and WNL Stars

Abstract

From new high signal-to-noise ratio (S/N) 1È2.2 km spectroscopy of nine extreme early-type starsÈ including O Iaf, O Iafpe and WN9 typesÈwe 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 spectroscopy alone, an analysis technique important to studies of luminous stars in the Galactic center and other galaxies. Derived stellar parametersÈmass-loss rates, luminosities, surface abundances, temperaturesÈshow good agreement between optical and near-IR analyses, provided that IR data are of sufficient spectral resolution (R [ 2000) and S/N (S/N [ 30). Wind velocities derived from He I 1.0830 km are consistent with those from ultraviolet P Cygni proÐles. Temperatures 200È1300 K systematically lower are determined from the near-IR diagnostics, a di †erence not signiÐcant in determining the stellar properties of these objects ; which set of spectral lines provides the more accurate physical parametersÈoptical or IRÈcannot at present be ascertained. The strength of He I 2.0581 km is very sensitive to the extreme ultraviolet energy distribution where line blanketing by heavy elements plays an important role ; this line should not on its own be considered a reliable temperature diagnostic. The three peculiar, extreme emission-line starsÈthe O Iafpe stars HD 152386, HD 152408, and HDE 313846Èare more similar in both morphological and physical characteristics to WNL-type Wolf-Rayet stars than to normal O Iaf supergiants and should be classiÐed as W-R. Their classiÐcation should be WN9ha, in which they remain a unique subgroup.