New constraints on the disk characteristics and companion candidates around T Chamaeleontis with VLT/SPHERE^⋆

¹ Max Planck Institute for Astronomy Königstuhl 17 69117 Heidelberg Germany
² Heidelberg University, Institute of Theoretical Astrophysics, Albert-Ueberle-Str. 2, 69120 Heidelberg, Germany
³ INAF-Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁴ Dipartimento di Fisica e Astronomia “G. Galilei”, Universita’ degli Studi di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
⁵ CRAL, UMR 5574, CNRS, Université Lyon 1, 9 avenue Charles André, 69561 Saint Genis Laval Cedex, France
⁶ Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
⁷ European Southern Observatory, Alonso de Córdova 3107, Casilla 19001 Vitacura, Santiago 19, Chile
⁸ Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands
⁹ Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
¹⁰ Instituto de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Av. Gran Bretaña 1111, Playa Ancha, Valparaíso, Chile
¹¹ ICM nucleus on protoplanetary disks, Protoplanetary discs in ALMA Early Science, Universidad de Valparaíso, Valparaíso, Chile
¹² Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
¹³ Institute for Astronomy, The University of Edinburgh, Royal Observatory, Blackford Hill View, Edinburgh, EH9 3HJ, UK
¹⁴ LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, Univ. Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
¹⁵ Institute for Astronomy, ETH Zurich, Wolfgang-Pauli-Strasse 27, 8093 Zurich, Switzerland
¹⁶ Department of Astronomy, Stockholm University, AlbaNova University Center, 10691 Stockholm, Sweden
¹⁷ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
¹⁸ Núcleo de Astronomía, Facultad de Ingeniería, Universidad Diego Portales, Av. Ejercito 441, Santiago, Chile
¹⁹ Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
²⁰ Observatoire Astronomique de l’Université de Genève, 51 Ch. des Maillettes, 1290 Versoix, Switzerland
²¹ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany

^⋆⋆ Corresponding author: A. Pohl, e-mail: pohl@mpia.de

Received: 12 December 2016
Accepted: 9 May 2017

Abstract

Context. The transition disk around the T Tauri star T Cha possesses a large gap, making it a prime target for high-resolution imaging in the context of planet formation.

Aims. We aim to find signs of disk evolutionary processes by studying the disk geometry and the dust grain properties at its surface, and to search for companion candidates.

Methods. We analyze a set of VLT/SPHERE data at near-infrared and optical wavelengths. We performed polarimetric imaging of T Cha with IRDIS (1.6 μm) and ZIMPOL (0.5–0.9 μm), and obtained intensity images from IRDIS dual-band imaging with simultaneous spectro-imaging with IFS (0.9–1.3 μm).

Results. The disk around T Cha is detected in all observing modes and its outer disk is resolved in scattered light with unprecedented angular resolution and signal-to-noise. The images reveal a highly inclined disk with a noticeable east-west brightness asymmetry. The significant amount of non-azimuthal polarization signal in the U_φ images, with a U_φ/Q_φ peak-to-peak value of 14%, is in accordance with theoretical studies on multiple scattering in an inclined disk. Our optimal axisymmetric radiative transfer model considers two coplanar inner and outer disks, separated by a gap of 0.̋28 (~30 au) in size, which is larger than previously thought. We derive a disk inclination of ~69 deg and PA of ~114 deg. In order to self-consistently reproduce the intensity and polarimetric images, the dust grains, responsible for the scattered light, need to be dominated by sizes of around ten microns. A point source is detected at an angular distance of 3.5′′ from the central star. It is, however, found not to be co-moving.

Conclusions. We confirm that the dominant source of emission is forward scattered light from the near edge of the outer disk. Our point source analysis rules out the presence of a companion with mass larger than ~8.5 M_jup between 0.̋1 and 0.̋3. The detection limit decreases to ~2 M_jup for 0.̋3 to 4.0′′.