Discovery of extended radio emission in the young cluster Wd1
Abstract
We present 10-μm 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 ~ 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[e] 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 μm 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~10^3yr). 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.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- October 1998
- DOI:
- 10.1046/j.1365-8711.1998.02038.x
- arXiv:
- arXiv:astro-ph/9807303
- Bibcode:
- 1998MNRAS.299L..43C
- Keywords:
-
- STARS: EMISSION-LINE;
- BE;
- STARS: INDIVIDUAL: ARA C;
- Astrophysics
- E-Print:
- 5 pages including encapsulated figures, figure 3 separate. Accepted for MNRAS pink pages