Near-IR spectroscopy of OB stars with VLT/CRIRES
Max-Planck-Institute for Astrophysics, Karl-Schwarzschild-Str. 1, D-85741 Garching, Germany
Dr. Karl Remeis-Observatory & ECAP, Sternwartstr.7, D-96049 Bamberg, Germany
Physics Department, University of California, Davis, CA 95616, USA, and Institut für Astrophysik, Georg-August-Universität Göttingen, Friedrich-Hund Platz 1, D-37077, Germany
Universitätssternwarte München, Scheinerstr. 1, D-81679 München, Germany
ESO Garching, Karl-Schwarzschild-Str. 2, D-85784 Garching, Germany
ESO Santiago, Alonso de Córdova 3107, Casilla 19001, Santiago 19, Chile
Abstract
We have conducted a pilot observational programme in order to obtain very high resolution near-IR spectra (R~100 000) with wide wavelength coverage in the JHKL bands of early B-type stars with CRIRES on the VLT. The sample comprises a B0.2V, a B0 III and a B1.5 III star, which have already been thoroughly analysed by us in previous work in the optical. The stars span a range of about 9000K in effective temperature, thus covering different ions of several elements. A novel data reduction technique was carried out which facilitated telluric lines removal by precise modelling of the Earth’s atmospheric spectrum. We investigate to what extent it is possible to derive atmospheric parameters and chemical abundances of early B-type stars from near- IR spectroscopy only. For this purpose we have extended our non-LTE spectral modelling to applications in the near-IR, based on our state-of-the-art model atoms that were thoroughly tested previously in the optical. Most H, He, C, N, O, Mg and Si lines in the near-IR (some of them resolved for the first time) could be reproduced, allowing atmospheric parameters and chemical abundances to be derived. Some remaining discrepancies between synthetic and observed strong lines, and some lines unidentified due to a lack of atomic data need to be investigated further. We have succesfully tested our modelling techniques and quantitative spectral analysis in the near-IR at high resolution and obtained excellent agreement with previous precision work in the optical. This will allow us to perform reliable spectral analyses of early B-type stars that suffer from strong optical extinction in the future, based on near-IR observations alone.