When giant planets form in protoplanetary disks, they are expected to dynamically clear out a gap. During this transition phase while the planet is still forming, gap-crossing gas streams are expected to continue accreting material onto the growing planet from the over-density at the outer gap edge. Large dust grains are expected to pile-up at the outer gap edge, while small grains can cross the gap with the gas.
The near face-on transitional disk HD142527 offers an excellent 'laboratory' to study planet formation in action. ALMA 345 GHz continuum and ATCA 34 GHz (7-mm band) images show that the dust emission is shaped like a horseshoe in the outer disk, while ALMA CO (3-2) observations show residual gas inside the cavity and denser HCO+ gas in gap-crossing filaments. The ATCA 7mm observations show a peak in the dust flux in the horseshoe, corresponding to molecular line decrements (in both CO and HCO+), as well as diffuse 7mm emission roughly corresponding to the ALMA filaments where no counterpart is seem in the 345 GHz continuum. We discuss the implications for planet formation in this intriguing transitional disk.