Radio observations of HD 93129A: The earliest O star with the highest mass loss?

Free access article

Issue		A&A Volume 416, Number 1, March II 2004


Page(s)		171 - 178
Section		Interstellar and circumstellar matter
DOI		http://dx.doi.org/10.1051/0004-6361:20034138

A&A 416, 171-178 (2004)
DOI: 10.1051/0004-6361:20034138

Radio observations of HD 93129A: The earliest O star with the highest mass loss?

P. Benaglia^{1, 2} and B. Koribalski³

¹ Instituto Argentino de Radioastronomía, C.C. 5, 1894 Villa Elisa, Argentina
² Facultad de Cs. Astronómicas y Geofísicas, UNLP, Paseo del Bosque S/N, 1900, La Plata, Argentina
³ Australia Telescope National Facility, CSIRO, PO Box 76, Epping, NSW 1710, Australia

(Received 31 July 2003 / Accepted 6 November 2003 )

Abstract
We present the results of radio continuum observations towards the open cluster Tr 14, where our main targets are the early-type O stars HD 93129A/B and HD 93128. The observations were carried out at 3 cm (8.64 GHz) and 6 cm (4.80 GHz) with the Australia Telescope Compact Array. Only HD 93129A (type O2 If*) was detected; we measure flux densities of $S_{\rm 3~cm} = 2.0\, \pm\, 0.2$ mJy and $S_{\rm 6~cm} = 4.1\, \pm\, 0.4$ mJy. The resulting spectral index of $\alpha = -1.2\, \pm\, 0.3$ ( $S_\nu \propto \nu^\alpha$ ) indicates predominantly non-thermal emission, suggesting HD 93129A may be a binary system. We propose that the observed 3 cm radio emission is mostly coming from the non-thermal wind collision region of a binary, and, to a lesser extent, from the thermal winds of the primary and secondary stars in HD 93129A. At a stellar distance of 2.8 kpc, we derive a mass-loss rate $\dot{M} = 5.1 \times 10^{-5}$ $M_{\odot}$ yr ^-1, assuming the thermal fraction of the 3 cm emission is ~0.5.

Key words: stars: individual: HD 93129A, HD 93129B, HD 93128 -- stars: mass-loss -- stars: winds, outflows -- radio continuum: stars

Offprint request: P. Benaglia, paula@lilen.fcaglp.unlp.edu.ar

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