Identifying Anticyclonic Vortex Features Produced by the Rossby Wave Instability in Protoplanetary Disks

Pinghui Huang,Hui Li,Shengtai Li,Andrea Isella,Jianghui Ji

doi:10.3847/1538-4357/aae317

Abstract

Abstract Several nearby protoplanetary disks have been observed to display large-scale crescents in the (sub)millimeter dust continuum emission. One interpretation is that these structures correspond to anticyclonic vortices generated by the Rossby wave instability within the gaseous disk. Such vortices have local gas overdensities and are expected to concentrate dust particles with a Stokes number around unity. This process might catalyze the formation of planetesimals. Whereas recent observations showed that dust crescents are indeed regions where millimeter-size particles have abnormally high concentration relative to the gas and smaller grains, no observations have yet shown that the gas within the crescent region counterrotates with respect to the protoplanetary disk. Here we investigate the detectability of anticyclonic features through measurement of the line-of-sight component of the gas velocity obtained with ALMA. We carry out 2D hydrodynamic simulations and 3D radiative transfer calculations of a protoplanetary disk characterized by a vortex created by the tidal interaction with a massive planet. As a case study, the disk parameters are chosen to mimic the IRS 48 system, which has the most prominent crescent observed to date. We generate synthetic ALMA observations of both the dust continuum and 12CO emission around the frequency of 345 GHz. We find that the anticyclonic features of the vortex are weak but can be detected if both the source and the observational setup are properly chosen. We provide a recipe for maximizing the probability of detecting such vortex features and present an analysis procedure to infer their kinematic properties.

Highlights

Protoplanetary systems such as IRS 48, LkHα 330 (Isella et al 2013), HD 142527 (Muto et al 2015), MWC 758 (Isella et al 2010), and SAO 206462 (Pérez et al 2014) exhibit large cavities and prominent crescents in themillimeter dust continuum emission
In systems where spatially resolved multiwavelength observations of both dust and gas emission exist, namely IRS 48, HD 142527, and MWC 758, the continuum crescents appear to originate from the azimuthal and radial concentration of solid particles toward local maxima of the gas pressure (Casassus et al 2015; van der Marel et al 2015; Boehler et al 2017). Such concentration is believed to result from the decoupling between dust and gas and subsequent migration of solid particles in the direction of the gas pressure gradient. This interpretation is supported by the fact that gas–dust decoupling is most efficient for grains with a Stokes number around unity, which, for typical densities of protoplanetary disks, correspond to grains that emit mostly atmillimeter wavelengths
ALMA observations have revealed azimuthal asymmetries in several protoplanetary disks that are thought to trace largescale vortices produced by the Rossby wave instability (RWI) excited by planet–disk interactions

Summary

Introduction

Protoplanetary systems such as IRS 48 (van der Marel et al 2013), LkHα 330 (Isella et al 2013), HD 142527 (Muto et al 2015), MWC 758 (Isella et al 2010), and SAO 206462 (Pérez et al 2014) exhibit large cavities and prominent crescents in the (sub)millimeter dust continuum emission. In systems where spatially resolved multiwavelength observations of both dust and gas emission exist, namely IRS 48, HD 142527, and MWC 758, the continuum crescents appear to originate from the azimuthal and radial concentration of solid particles toward local maxima of the gas pressure (Casassus et al 2015; van der Marel et al 2015; Boehler et al 2017) Such concentration is believed to result from the decoupling between dust and gas and subsequent migration of solid particles in the direction of the gas pressure gradient (see, e.g., Weidenschilling 1977; Birnstiel et al 2013).

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