Infrared Observations of HDE 226868/CYG X-1 and HDE 245770/AO535+26
We know from Copernicus ultraviolet observations that all O-type stars are losing mass by stellar wind. The ionized expanding circumstellar envelope formed by the stellar wind is emitting through free-free and bound-free radiation processes. This radiation is detectable at the infrared wavelengths where the stellar continuum is negligible. The measurement of the IR excess (defined as the difference between the total flux and the stellar continuum at a given wavelength) and the knowledge of the terminal velocity of the envelope, allow us to derive for OB stars the mass loss rate. From the analysis of our IR observations of two O stars, HDE 226868 and HDE 245770, identified as optical counterpart of X-ray sources, we give an estimate of their mass loss rate. The IR observations were carried out with the Jungfraujoch 76 cm telescope using a GE bolometer with a focal plane chopping system and with the Merate 132 cm telescope using an InSb detector.
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