Near-Infrared Spectroscopy of Galactic Wolf-Rayet Stars

Abstract

We present high-quality near-IR spectra of 24 Galactic WR stars, of a broad range of subtypes, selected as having known distances. The data cover the region 0.97μm–1.12μm and include the λ10830-Å He I triplet. Measurements of He I and He II lines, together with the absolute magnitudes, yield temperatures, luminosities, mass-loss rates, and terminal velocities for our sample. We extend that sample by including results for a further 12 stars of known distance, taken from the literature. The spectroscopic mass-loss rates are in excellent agreement with those estimated from radio data, and exceed the ‘single-scattering limit’ by large factors. Mass-loss rates depend only weakly on mass, but there is a tight correlation between surface mass flux and temperature. Terminal velocities correlate loosely with subtype for both WR sequences. Principally because of revisions to the adopted absolute magnitudes, our luminosities average slightly fainter than found previously; that exacerbates discrepancies with the predictions of evolutionary models, but reconciles results for Galactic and LMC stars. However, comparison with core-helium-burning mass-luminosity tracks suggests that the spectroscopic luminosities may be systematically too faint by ∼0.5 dex. We suggest that the WNC stars in our sample may represent an intermediate phase between WNL and WCE subtypes. A full version of this paper is being submitted to Astronomy & Astrophysics.