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Radio flux variations of WR 140 | |||||
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Like all hot, luminous stars, WR 140 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 O5 stellar winds results in the acceleration of electrons to relativistic energies and, given a magnetic field, 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. There is a good correlation [4] between observation of non-thermal radiation from WR systems and their separation as inferred from their periods; in the widest systems like WR 147, it is observed all the time. In the case of WR 140, 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 [5] 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 WR 140 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] |
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| Right: A montage of 8.4-GHz VLBA observations of WR 140 at orbital phases 0.73, 0.85 and 0.93 showing rotation of the radio source and wind-collision region as the orbit progressed. The inferred positions of the O5 star are marked on the orbit deduced by Dougherty et al.[6] from the VLBA observations, together with the RV orbit, and the separation of the stars[5]. |  |
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rev: 29 Feb 2016 Peredur Williams [Home page] |
[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 & P.M. Williams MNRAS 319, 1005, 2000 [5] J.D. Monnier et al. ApJL 602, 57, 2004 [6] S.M. Dougherty et al. ApJ 623, 447, 2005 [7] J.M. Pittard & S.M. Dougherty MNRAS 372, 801, 2006 |