Colliding-wind Binary Stars | ||||||||||
Links
|
The significance of colliding
stellar winds in massive binaries was first recognized for X-ray
production, with the suggestion [1] that collision
of a WR stellar wind with that from a companion OB star could be a
significantly stronger source of X-rays than collision of the WR wind
with the OB star itself . A survey of X-ray emission from WR stars
[2] observed with EINSTEIN confirmed that
binaries incorporating WR stars were stronger X-ray sources than single
WR stars. As it happened, WR 140 was not observed with EINSTEIN
but it has been observed with most other X-ray missions.
Its X-ray emission was found to vary with the
orbit, suffering highest extinction at the
time of periastron passage, indicating movement of the X-ray source deep
into the WR wind, consistent with its originating between the two stars
[3], [9]. Colliding winds and X-ray production by WR 140
have been modelled both analytically [4] and
numerically [5]. The non-thermal
radio emission from WR140 varies similarly,
being extinguished around periastron.
For direct observation of non-thermal radio emission and other colliding-wind phenomena between two luminous stars, we need to look to a wide colliding-wind WR system, like WR 147, whose radio and stellar components have been spatially resolved [6] as below. The X-ray emission from WR 147 arises [7] from the same region as the non-thermal radio emission, which has since been modelled theoretically [8]. |
|||||||||
Right: Direct evidence of a colliding-wind origin for non-thermal radio emission from the wide binary WR 147 (AS431). The radio emission is double, as can be seen in this contour map made with MERLIN. The separation of the radio sources is slightly less than that of the stars [6]. The southern radio source is the stellar wind emission from the WN8 star, which is evidently rather clumpy. The northern radio source is non-thermal emission from the region where the WN8 stellar wind collides with that of the OB star. This occurs between the two stars and is closer to the OB star because it has a weaker stellar wind than the WN8 star. The collision region is clearly elongated East-West. | ||||||||||
|
[1] O.F. Prilutskii & V.V. Usov,
Soviet
Ast. 20, 2, 1976 (translation) [2] A.M.T. Pollock, ApJ., 320, 283, 1987 [3] P.M. Williams et al. MNRAS 243, 662, 1990 [4] V.V. Usov, ApJ, 389, 635, 1992 [5] I.R Stevens, J. Blondin & A.M.T. Pollock, ApJ, 386, 265, 1992 [6] P.M. Williams et al. MNRAS 289, 10, 1997 [7] J.M. Pittard et al. A&A 388, 335, 2002 [8] S.M. Dougherty et al. A&A, 409, 217, 2003 [9] Y. Suguwara et al. PASJ, 67, 121, 2015 |