2006A&A...460L..43P

We constrain the dust distribution and its properties (temperature, emissivity) in inner proto-planetary disks We performed sub-arcsecond high-sensitivity interferometric observations of the thermal dust emission at 1.4mm and 2.8mm in the disks surrounding LkCa15 and MWC480, with the new 750 m baselines of the IRAM PdBI array. This provides a linear resolution of ∼60AU at the distance of Taurus. We report the existence of a cavity of ∼50AU radius in the inner disk of LkCa15. Whereas LkCa15 emission is optically thin, the optically thick core of MWC480 is resolved at 1.4 mm with a radius of ∼35AU, constraining the dust temperature. In MWC480, the dust emission is coming from a colder layer than the CO emission, most likely the disk mid-plane. These observations provide direct evidence of an inner cavity around LkCa15. Such a cavity most probably results from the tidal disturbance created by a low-mass companion or large planet at ∼30AU from the star. These results suggest that planetary system formation is already at work in LkCa15. They also indicate that the classical steady-state viscous disk model is too simplistic a description of the inner 50AU of ``proto-planetary'' disks and that the disk evolution is coupled to the planet formation process. The MWC480 results indicate that a proper estimate of the dust temperature and size of the optically thick core are essential for determining the dust emissivity index β.