Self-consistent modelling of the dust component in protoplanetary and circumplanetary disks: the case of PDS 70

TL;DR

This paper develops a 3D radiative transfer model for the PDS 70 system to understand dust distribution and properties of the planetary companion PDS 70 c and its circumplanetary disk, matching observations at multiple wavelengths.

Contribution

It introduces a self-consistent model that explains the global features of PDS 70 in submillimeter and scattered light, revealing dust segregation and constraining the circumplanetary disk's dust mass.

Findings

Presence of dust grain segregation in the protoplanetary disk

Optically thick circumplanetary disk around PDS 70 c with dust mass < 0.7 Earth masses

Planet luminosity dominates dust heating within 0.6 au

Abstract

Direct observations of young stellar objects are important to test established theories of planet formation. PDS 70 is one of the few cases where robust evidence favours the presence of two planetary mass companions inside the gap of the transition disk. Those planets are believed to be going through the last stages of accretion from the protoplanetary disk, a process likely mediated by a circumplanetary disk (CPD). We aim to develop a three dimensional radiative transfer model for the dust component of the PDS 70 system which reproduces the system's global features observed at two different wavelengths: 855 $\mu\, \mathrm{m}$ with ALMA and 1.25 $\mu\, \mathrm{m}$ with VLT/SPHERE. We use this model to investigate the physical properties of the planetary companion PDS 70 c and its potential circumplanetary disk. We select initial values for the physical properties of the planet and CPD through appropriate assumptions about the nature and evolutionary stage of the object. We modify iteratively the properties of the protoplanetary disk until the predictions retrieved from the model are consistent with both data sets. We provide a model that jointly explains the global features of the PDS 70 system seen in submillimeter and polarised-scattered light. Our model suggests that spatial segregation of dust grains is present in the protoplanetary disk. The submillimeter modelling of the PDS 70 c source favours the presence of an optically thick CPD and places an upper limit to its dust mass of 0.7 $M_\oplus$. Furthermore, analysis of the thermal structure of the CPD demonstrates that the planet luminosity is the dominant heating mechanism of dust grains inside 0.6 au from the planet while heating by stellar photons dominates at larger planetocentric distances.