The circumstellar disc around the Herbig AeBe star HD169142

Abstract

We present 7 mm and 3.5 cm wavelength continuum observations towards the Herbig AeBe star HD169142 performed with the Very Large Array (VLA) with an angular resolution of 1 arcsec. We find that this object exhibits strong ( 4.4 mJy), unresolved ( 1 arcsec) 7 mm continuum emission, being one of the brightest isolated Herbig AeBe stars ever detected with the VLA at this wavelength. No emission is detected at 3.5 cm continuum, with a 3 upper limit of 0.08 mJy. From these values, we obtain a spectral index 2.5 in the 3.5 cm to 7 mm wavelength range, indicating that the observed flux density at 7 mm is most likely dominated by thermal dust emission coming from a circumstellar disc. We use available photometric data from the literature to model the spectral energy distribution (SED) of this object from radio to near-ultraviolet frequencies. The observed SED can be understood in terms of an irradiated accretion disc with low mass accretion rate, , surrounding a star with an age of 10 Myr. We infer that the mass of the disc is 0.04 M , and is populated by dust grains that have grown to a maximum size of 1 mm everywhere, consistent with the lack of silicate 10 m emission. These features, as well as indications of settling in the wall at the dust destruction radius, led us to speculate that the disc of HD169142 is in an advanced stage of dust evolution, particularly in its inner regions.