The radio structure of Menzel 3

We present the first radio continuum images of the evolved late-type stellar object, Menzel 3 (Mz 3), made with multifrequency observations using the Australia Telescope Compact Array. The maximum resolutions attained are 1, 2, 4 and 7 arcsec. At each frequency investigated, the large-scale radio structure is reminiscent of that seen at infrared and optical wavelengths. In the highest-frequency image of resolution 1 arcsec, the radio brightness distribution is dominated by a compact core emission feature, which we attribute to the ionization of either the last exhalation of the superwind (single progenitor scenario) or to the ongoing stellar wind from a companion (binary scenario). At the higher frequencies investigated, we find that this core ionized outflow is asymmetric, optically thick and has a spectral index consistent with that of thermal emission. The mass loss rate associated with the core emission feature is 7 × 10^-5 M_solar yr^-1. We discuss this outflow and favour its origin as being due to a companion. Extending from either side of the compact core, at PA ~ 120° with respect to the bipolar axis, we find evidence for wings of emission that may be due to the ionized inner surface of an equatorial collimating disc; this surface has dimensions 7 × 1.5 arcsec² (8800 × 1900 au² at 1.3 kpc). We suggest that this feature may be part of the circumbinary accretion disc suggested recently by Kastner et al. We measure low brightness temperatures, which we attribute to there being unresolved condensations on sub-arcsecond scales within the beam size.