Possible planet-forming regions on submillimetre images

Abstract

Submillimetre images of transition discs are expected to reflect the distribution of the optically thin dust. Former observation of three transition discs LkHa330, SR21N, and HD1353444B at submillimetre wavelengths revealed images which cannot be modelled by a simple axisymmetric disc. We show that a large-scale anticyclonic vortex that develops where the viscosity has a large gradient (e.g., at the edge of the disc dead zone), might be accountable for these large-scale asymmetries. We modelled the long-term evolution of vortices being triggered by the Rossby wave instability. We found that a horseshoe-shaped (azimuthal wavenumber m=1) large-scale vortex forms by coalescing of smaller vortices within 5x10^4 yr, and can survive on the disc life-time (~5x10^6 yr), depending on the magnitude of global viscosity and the thickness of the viscosity gradient. The two-dimensional grid-based global disc simulations with local isothermal approximation and compressible-gas model have been done by the GPU version of hydrodynamic code FARGO (GFARGO). To calculate the dust continuum image at submillimetre wavelengths, we combined our hydrodynamical results with a 3D radiative transfer code. By the striking similarities of the calculated and observed submillimetre images, we suggest that the three transition discs can be modelled by a disc possessing a large-scale vortex formed near the disc dead zone edge. Since the larger dust grains (larger than mm in size) are collected in these vortices, the non-axisymmetric submillimetre images of the above transition discs might be interpreted as active planet and planetesimal forming regions situated far (> 50 AU) from the central stars.Comment: 13 pages, 14 figures, accepted for publication in MNRA

Slowly-growing gap-opening planets trigger weaker vortices

“…Regály et al 2012) are also expected to be elongated. As a result, one would not be able to distinguish the origin of elongated vortices (as induced by a dead zone boundary or a slowly-grown planet) based on azimuthal extent alone.…”

“…Such vortensity extrema often coincide with extrema in the disc's surface density profile, which can arise at dead zone boundaries (e.g. Lyra & Mac Low 2012;Regály et al 2012;Miranda et al 2016) and gap-edges created by giant planets (e.g. Li et al 2005).…”

Fingerprints of giant planets in the photospheres of Herbig stars

“…Cavities and gaps in transitional disks may arise due to dust being trapped in the outer disk by giant planets (Whipple 1972;Barge & Sommeria 1995;Rice et al 2006;Pinilla et al 2012;Zhu et al 2012), by gas and dust clearing owing to photoevaporation (Alexander et al 2006a(Alexander et al ,b, 2014Owen et al 2011Owen et al , 2012, or by the accumulation of gas and dust at the outer edge of a region with low ionization (Regály et al 2012;Flock et al 2015). The dominant mechanism should determine the volatile (gas) to refractory (dust) elemental ratios in the accretion columns that channel material onto the stellar photosphere.…”

The Gas Disk: Evolution and Chemistry

“…Nonaxisymmetric structures that emerge in the disk, such as spiral arms, clumps, and vortices, may serve as likely spots for dust accumulation and planetesimal formation, facilitating the formation of solid protoplanetary cores (Rice et al 2004;Nayakshin 2011;Regály et al 2012;Gibbons et al 2015). Gravitational instability and fragmentation in the early evolution of protostellar disks brings about a wealth of phenomena, the most important of which are briefly reviewed below.…”