Radio flux variations of WR140
Links WR140 orbital motion Colliding-wind binaries WR140 Introduction Episodic dust-makers WR Star Catalogue	Like all hot, luminous stars, WR140 emits free-free radiation from its stellar winds, readily observed in the radio because the winds are so extended. In addition, the collision of the WR and O winds results in the acceleration of electrons to relativistic energies and the production of synchrotron radiation between the two stars. This emission is intrinsically brighter than the free-free wind emission but, because it arises deep within the WR stellar wind, we can observe it only if the wind extinction along our sight-line to the synchrotron source is small enough. This occurs naturally in a wide binary like WR147. In the case of WR140, the extinction to the wind-collision region varies with the orbit, resulting in the periodic extinction and unveiling of the non-thermal source. Spectacular high-resolution VLBA imaging [4] of the non-thermal source shows it to have the curved shape expected from formation in the wind-collision region and to move round as the binary orbit progresses. The radio, X-ray and gamma-ray emission near radio maximum has been modelled by Pittard & Dougherty.
Right: Radio fluxes from WR140 at wavelengths of 6cm and 20 or 21 cm observed with the VLA or WSRT. The maximum emission is associated with minimum extinction along the sightline to the region between the stars where the synchrotron emission arises. Around periastron, only the thermal emission from the stellar wind is observed. [1],[2],[3]
References: rev: 30 Sep 2009 Peredur Williams	[1] P.M. Williams et al. MNRAS 243, 662, 1990 [2] P.M. Williams et al. A&A 291, 805, 1994 [3] R.L.White & R.H. Becker ApJ 451, 352, 1995 [4] S.M. Dougherty et al. ApJ 623, 447, 2005 [5] J.M. Pittard & S.M. Dougherty MNRAS 372, 801, 2006