Context :

Aims : We constrain the dust distribution and its properties ( temperature , emissivity ) in inner proto-planetary disks

Methods : We performed sub-arcsecond high-sensitivity interferometric observations of the thermal dust emission at 1.4 mm and 2.8 mm in the disks surrounding LkCa 15 and MWC 480 , with the new 750 m baselines of the IRAM PdBI array .
This provides a linear resolution of \sim 60 AU at the distance of Taurus .

Results : We report the existence of a cavity of \sim 50 AU radius in the inner disk of LkCa 15 .
Whereas LkCa 15 emission is optically thin , the optically thick core of MWC 480 is resolved at 1.4 mm with a radius of \sim 35 AU , constraining the dust temperature .
In MWC 480 , the dust emission is coming from a colder layer than the CO emission , most likely the disk mid-plane .

Conclusions : These observations provide direct evidence of an inner cavity around LkCa 15 .
Such a cavity most probably results from the tidal disturbance created by a low-mass companion or large planet at \sim 30 AU from the star .
These results suggest that planetary system formation is already at work in LkCa 15 .
They also indicate that the classical steady-state viscous disk model is too simplistic a description of the inner 50 AU of “ proto-planetary ” disks and that the disk evolution is coupled to the planet formation process .
The MWC 480 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 \beta .