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

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. <BR /> 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. <BR /> 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). <BR /> 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<SUB>φ</SUB> images, with a U<SUB>φ</SUB>/Q<SUB>φ</SUB> 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. <BR /> 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<SUB>jup</SUB> between 0.̋1 and 0.̋3. The detection limit decreases to 2 M<SUB>jup</SUB> for 0.̋3 to 4.0''. <P />Based on observations made with European Southern Observatory (ESO) telescopes at the Paranal Observatory in Chile, under program IDs 095.C-0298(B), 096.C-0248(B) and 096.C-0248(C).