Quantitative near-ir spectroscopy of ob stars

Abstract

Massive OB-type stars are associated with star-formation regions. Their high luminosity allows us to derive present-day chemical abundances over large distances, in the Milky Way and the Magellanic Clouds. We discuss first quantitative results from an analysis of high-quality spectra of early B-type stars in the solar vicinity obtained with CRIRES on the VLT/UT1. This work includes the identification of metal lines never resolved before and benchmark tests of spectrum synthesis, which is more challenging than in the optical because of the amplification of non-LTE effects in the near-IR. Results from the visual and near-IR spectra agree for those elements with reliably calibrated model atoms. The ionisation equilibria of HeI/II and CII/III are established simultaneously for both spectral ranges, which confirms the self-consistency of the analysis. This will allow us to derive reliable chemical abundances in (dust-enshrouded) regions throughout the Galactic disk, which are observable only at near-IR wavelengths. Moreover, an accurate modelling of early-type star spectra is important for the use of these objects as telluric standards for other spectroscopic investigations in the near-IR. This pioneering work is part of our preparation for the science to be done with the next generation of ELTs.