MERLIN observations of the Wolf–Rayet star AS431 (WR147)-a double radio source

Abstract

THE Wolf–Rayet star AS431 (number 147 in ref. 1) is known to be bright at X-ray and radio wavelengths^2,3, and previous radio-interferometric observations indicate that it has an extended struc-ture³. Here we report new interferometric observations of AS431 using MERLIN (the Jodrell Multi-Element Radio Linked Inter-ferometer Network), in which the sensitivity was sufficient to map the stellar thermal-continuum radio emission with a beam size of 0.1 arcsec. The object is resolved into two radio sources, separated by 0.6 arcsec, corresponding to a spatial separation of 1,100 AU at the assumed distance of 1.9 kpc. The computed brightness of the two sources, ∼10,000 K, is typical of optically thick thermal emission from a stellar wind, but compared with other observations²suggests that some part of the emission is non-thermal. One of the radio components corresponds to the position of the single source revealed by accurate optical observations. We simulate the observed total radio spectrum with a two-component model for the emission.