DISCOVERY OF EXTENDED RADIO-EMISSION IN THE YOUNG CLUSTER WD1

We present 10-mu m ISO-SWS and Australia Telescope Compact Array obser vations of the region in the cluster Wd1 in Ara centred on the B [e] s tar Ara C. An ISO-SWS spectrum reveals emission from highly ionized sp ecies in the vicinity of the star, suggesting a secondary source of ex citation 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 sim ilar to 14 arcsec, The westerly source is resolved, with a spectral in dex indicative of thermal emission. The easterly source is clearly ext ended and non-thermal (synchrotron) in nature. Positionally, the B le] star is found to coincide with the more compact radio source, while t he 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 emissio n 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 ori gin in a detatched shell of material around the central star is theref ore suggested; however given the spatial extent of the emission, such a shell must be relatively young (tau similar to 10(3) yr), The extend ed 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 e xpected if a compact companion were present.