Spatial segregation of dust grains in transition disks

M Villenave,A Garufi,M Benisty,M Keppler,J Pragt,F Ménard,A Pavlov,W R F Dent,J Olofsson,C Dominik,G Van Der Plas,A Juhász,C Ginski,C Pinte,J Ramos,A Zurlo,P Pinilla,J De Boer,M Carle,L Weber,Misato Fukagawa ,Thomas Henning ,Laura Pérez ,Philippe Feautrier ,G A Muro-Arena ,Eric Stadler ,Mario Flock ,Jean-François Sauvage ,Jonathan P Williams ,Jun Ichi Morino

doi:10.1051/0004-6361/201834800

Abstract

Context. The mechanisms governing the opening of cavities in transition disks are not fully understood. Several processes have been proposed, but their occurrence rate is still unknown. Aims. We present spatially resolved observations of two transition disks, and aim at constraining their vertical and radial structure using multiwavelength observations that probe different regions of the disks and can help understanding the origin of the cavities. Methods. We have obtained near-infrared scattered light observations with VLT/SPHERE of the transition disks 2MASS J16083070-3828268 (J1608) and RXJ1852.3-3700 (J1852), located in the Lupus and Corona Australis star-forming regions respectively. We complement our datasets with archival ALMA observations, and with unresolved photometric observations covering a wide range of wavelengths. We performed radiative transfer modeling to analyze the morphology of the disks, and then compare the results with a sample of 20 other transition disks observed with both SPHERE and ALMA. Results. We detect scattered light in J1608 and J1852 up to a radius of 0.54′′ and 0.4′′ respectively. The image of J1608 reveals a very inclined disk (i ~ 74°), with two bright lobes and a large cavity. We also marginally detect the scattering surface from the rear-facing side of the disk. J1852 shows an inner ring extending beyond the coronagraphic radius up to 15 au, a gap and a second ring at 42 au. Our radiative transfer model of J1608 indicates that the millimeter-sized grains are less extended vertically and radially than the micron-sized grains, indicating advanced settling and radial drift. We find good agreement with the observations of J1852 with a similar model, but due to the low inclination of the system, the model remains partly degenerate. The analysis of 22 transition disks shows that, in general, the cavities observed in scattered light are smaller than the ones detected at millimeter wavelengths. Conclusions. The analysis of a sample of transition disks indicates that the small grains, well coupled to the gas, can flow inward of the region where millimeter grains are trapped. While 15 out of the 22 cavities in our sample could be explained by a planet of less than 13 Jupiter masses, the others either require the presence of a more massive companion or of several low-mass planets.

Highlights

The variety of physical and structural conditions in protoplanetary disks – the birthplace of planets – might be responsible for the diversity observed in the exoplanet population
A similar conclusion was reached on several other transition disks, which show a CO cavity smaller than the millimeter dust cavity, such as Sz 91 (Canovas et al 2015, 2016) or RXJ1604.3-2130A (Zhang et al 2014) for example. In each of these systems, the authors found the CO to extend at least 20 au inward of the outer edge of the millimeter dust cavity. These differences in inner radius could be related to the mechanisms responsible for the cavities in transition disks, which we explore in the subsection
We present new polarized scattered light observations of two transition disks, namely 2MASS J160830703828268 (J1608) and RXJ1852.3-3700 (J1852)

Summary

Introduction

The variety of physical and structural conditions in protoplanetary disks – the birthplace of planets – might be responsible for the diversity observed in the exoplanet population. Studying disk evolution through the analysis of protoplanetary disks with depleted regions and/or clear signs of evolution could provide indirect constraints on the way in which planets form. Thanks to new capabilities of high resolution instruments such as ALMA, VLT/SPHERE and Gemini/GPI, many features have been identified in protoplanetary disks and in particular in transition disks (TDs). Interacting with the disk can form such structures. The observation and/or hints of forming planets within disks have been reported in recent studies (Keppler et al 2018; Pinte et al 2018; Teague et al 2018)

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Discussion

Conclusion