Near Infrared Observations of Galactic WN Stars

Abstract

The observations reported here have been obtained with the ESO Reticon system attached to the Boller and Chivens spectrograph at the 3.6 m telescope. The reciprocal dispersion was 228 A mm⁻¹ with a useful spectral range extending from 5800 A to 11000 A. The slit was 200 pm wide which corresponds to 1.4 arcsec on the sky and to about 33.5 μm(∿ 7.6 A) in the plane of the detector. Sky substraction was performed by means of observations at 93 arcsec. East and West of the object. The correction for atmospheric extinction was based on a mean extinction curve of La Silla (Tug, 1977). As a consequence the strongest atmospheric bands are still present on the final spectra. The data were also corrected for the instrument sensitivity response by using calibrated stars selected from Breger’s catalog (1976). As these reference data are from filter photometry, they are not well suited to the resolution of our spectra, at least in some regions. This problem can be significant, as clearly illustrated by Johnson (1980).