Modelling accretion in transitional disks

Abstract

Context. Transitional disks are protoplanetary disks around young stars that display inner holes in the dust distribution within a few au that are accompanied by some gas accretion onto the central star. These cavities could possibly be created by the presence of one or more massive planets that opened a large gap or even cleared the whole inner region. Aims. If the gap is created by planets and gas is still present in it, then there should be a flow of gas past the planet into the inner region. It is our goal to study in detail the mass accretion rate into this planet-created gap in transitional disks and in particular the dependency on the planet's mass and the thermodynamic properties of the disk. Methods. We performed 2D hydrodynamical simulations using the grid-based FARGO code for disks with embedded planets. We added radiative cooling from the disk surfaces, radiative diffusion in the disk midplane, and stellar irradiation to the energy equation to have more realistic models. Results. The mass flow rate into the gap region depends, for given disk thermodynamics, non-monotonically on the mass of the planet. Generally, more massive planets open wider and deeper gaps which would tend to reduce the mass accretion into the inner cavity. However, for larger mass planets the outer disk becomes eccentric and the mass flow rate is enhanced over the low mass cases. As a result, for the isothermal disks the mass flow is always comparable to the expected mass flow of unperturbed disks Ṁd, while for more realistic radiative disks the mass flow is very small for low mass planets (≤4 Mjup) and about 50% of Ṁd for larger planet masses. The critical planet mass that allows the disk to become eccentric is much larger for radiative disks than for purely isothermal cases. Conclusions. Massive embedded planets can reduce the mass flow across the gap considerably, to values of about an order of magnitude smaller than the standard disk accretion rate, and can be responsible for opening large cavities. The remaining mass flow into the central cavity is in good agreement with the observations. ©ESO 2013.