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

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

Corresponding author: P. Benaglia, paula@lilen.fcaglp.unlp.edu.ar

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 mJy and mJy. The resulting spectral index of () 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   yr^-1, assuming the thermal fraction of the 3 cm emission is ~0.5.