From dust to planets: the ALMA and VLA view of planet formation

Abstract

Over the last decade, the Atacama Large Millimeter/submillimeter Array (ALMA) made it possible to observe protoplanetary discs, the birth sites of planets, at unprecedented angular resolution and sensitivity, revolutionising our understanding of planet formation. When observed at high-enough angular resolution, protoplanetary discs show sequences of axisymmetric dark and bright substructures, colloquially referred to as “gaps and rings”. The origin of such substructures and the role that they play in the planet formation process are, however, still debated. Substructures are considered to be either the signposts of ongoing interactions between (proto-)planets and their hosting discs, or the ideal location for the formation of new planetary bodies. The best way to solve this “chicken and the egg” problem is characterising the physical properties of these gaps and rings. In this talk, I will first discuss recent attempts to observationally infer the size, density, and temperature of dust in these rings, relying on collecting and modelling multi-frequency, i.e. (sub-)mm to cm, continuum observations in a handful of well studied systems. In particular, I will focus on CI Tau, the only T Tauri star where a candidate hot Jupiter was detected using radial velocity techniques. My high-angular resolution and sensitivity ALMA and VLA continuum observations of this source, reveal that the dust density and size locally increase at the position of the bright rings, suggesting that dust trapping is taking place. I will also show how CI Tau's unique spectral energy distribution allows putting unprecedented constraints on dust composition in this system. Finally, I will introduce a new technique that combines these dust properties with gas kinematics to understand if bright rings might be prone to the formation of planetesimals under streaming instability (SI). In the case of HD 163296, the only source where dust properties and gas kinematics have been well constrained so far, my method reveals that the outermost (100 au) ring shows favourable conditions to trigger the SI.