Blomme, R.

published in Active OB-Stars: Laboratories for Stellare and Circumstellar Physics, 361, pp. 186 (2007)

Abstract: The thermal millimeter and radio continua of OB stars are formed in the stellar wind, at large distances from the surface (from ˜ 10 to ˜ 100R_*). Observations at these wavelengths therefore cover geometrical regions that cannot be studied in any other way. The continuum fluxes at long wavelengths are determined by both the mass-loss rate and by the structure that may be present. By using a range of wavelengths one can detect changes of structure with distance. We found evidence that the amount of structure decreases with distance in the stellar wind. The B0 supergiant ɛ Ori is an especially good example of a star showing this effect. Non-thermal radio fluxes were previously thought to be another indicator of structure in the stellar wind. The work of tet{VanLoo+al05} has shown, however, that these non-thermal radio emitters are most probably all colliding-wind systems. A preliminary reduction of recent millimeter observations of ζ Pup shows variability on the 19.6-hr period. If confirmed, this indicates that Corotating Interaction Regions are an important component of structure at distances beyond 10{R}_*.

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