Discovery of extended radio emission in the young cluster Wd1

We present 10-mu m ISO-SWS and Australia Telescope Compact Array observations of the region in the cluster Wd1 in Ara centred on the B [e] star Ara C. An ISO-SWS spectrum reveals emission from highly ionized species in the vicinity of the star, suggesting a secondary source of excitation in the region. We find strong radio emission at both 3.5 and 6.3 cm, with a total spatial extent-of over 20 arcsec. The emission is found to be concentrated in two discrete structures, separated by similar to 14 arcsec, The westerly source is resolved, with a spectral index indicative of thermal emission. The easterly source is clearly extended and non-thermal (synchrotron) in nature. Positionally, the B le] star is found to coincide with the more compact radio source, while the southerly lobe of the extended source is coincident with Ara A, an M2 I star. Observation of the region at 10 mu m reveals strong emission with an almost identical spatial distribution to the radio emission. Ara C is found to have an extreme radio luminosity in comparison with prior radio observations of hot stars such as O and B supergiants and Wolf-Rayet stars, given the estimated distance to the cluster. An origin in a detatched shell of material around the central star is therefore suggested; however given the spatial extent of the emission, such a shell must be relatively young (tau similar to 10(3) yr), The extended non-thermal emission associated with the M star Ara A is unexpected; to the best of our knowledge this is a unique phenomenon. SAX (2-10 keV) observations show no evidence of X-ray emission, which might be expected if a compact companion were present.