Shadows cast on the transition disk of HD 135344B
Multiwavelength VLT/SPHERE polarimetric differential imaging⋆
1 Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH, Amsterdam The Netherlands
2 Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
3 Millennium Nucleus “Protoplanetary Disks”, Chile
4 SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
5 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
6 ESO, Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago de Chile, Chile
7 Institute for Astronomy, ETH Zurich, Wolfgang-Pauli-Strasse 27, 8093 Zurich, Switzerland
8 Institute of Astronomy, Madingley Road, Cambridge CB3 OHA, UK
9 Université Grenoble Alpes, IPAG, 38000 Grenoble, France
10 CNRS, IPAG, 38000 Grenoble, France
11 LESIA, Observatoire de Paris, CNRS, Université Paris Diderot, Université Pierre et Marie Curie, 5 place Jules Janssen, 92190 Meudon, France
12 Max-Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
13 CRAL, UMR 5574, CNRS, Université Lyon 1, 9 avenue Charles André, 69561 Saint Genis Laval Cedex, France
14 Aix-Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
15 UMI-FCA, CNRS/INSU, UMI 3386, France
16 Université Nice-Sophia Antipolis, CNRS, Observatoire de la Côte d’Azur, Laboratoire J.-L. Lagrange, CS 34229, 06304 Nice Cedex 4, France
17 ONERA – Optics Department, 29 avenue de la Division Leclerc, 92322 Chatillon Cedex, France
18 NOVA Optical-Infrared Instrumentation Group at ASTRON, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
19 INAF–Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
20 European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
21 Geneva Observatory, University of Geneva, Chemin des Mailettes 51, 1290 Versoix, Switzerland
Received: 24 December 2015
Accepted: 14 September 2016
Context. The protoplanetary disk around the F-type star HD 135344B (SAO 206462) is in a transition stage and shows many intriguing structures both in scattered light and thermal (sub-)millimeter emission which are possibly related to planet formation processes.
Aims. We aim to study the morphology and surface brightness of the disk in scattered light to gain insight into the innermost disk regions, the formation of protoplanets, planet-disk interactions traced in the surface and midplane layers, and the dust grain properties of the disk surface.
Methods. We have carried out high-contrast polarimetric differential imaging (PDI) observations with VLT/SPHERE and obtained polarized scattered light images with ZIMPOL in the R and I-bands and with IRDIS in the Y and J-bands. The scattered light images and surface brightness profiles are used to study in detail structures in the disk surface and brightness variations. We have constructed a 3D radiative transfer model to support the interpretation of several detected shadow features.
Results. The scattered light images reveal with unprecedented angular resolution and sensitivity the spiral arms as well as the 25 au cavity of the disk. Multiple shadow features are discovered on the outer disk with one shadow only being present during the second observation epoch. A positive surface brightness gradient is observed in the stellar irradiation corrected (r2-scaled) images in southwest direction possibly due to an azimuthally asymmetric perturbation of the temperature and/or surface density by the passing spiral arms. The disk integrated polarized flux, normalized to the stellar flux, shows a positive trend towards longer wavelengths which we attribute to large (2πa ≳ λ) aggregate dust grains in the disk surface. Part of the non-azimuthal polarization signal in the Uφ image of the J-band observation can be attributed to multiple scattering in the disk.
Conclusions. The detected shadow features and their possible variability have the potential to provide insight into the structure of and processes occurring in the innermost disk regions. Possible explanations for the presence of the shadows include a 22° misaligned inner disk, a warped disk region that connects the inner disk with the outer disk, and variable or transient phenomena such as a perturbation of the inner disk or an asymmetric accretion flow. The spiral arms are best explained by one or multiple protoplanets in the exterior of the disk although no gap is detected beyond the spiral arms up to 1.′′0.
Key words: protoplanetary disks / planet-disk interactions / stars: individual: HD 135344B (SAO 206462) / methods: observational / instrumentation: high angular resolution / techniques: polarimetric
© ESO, 2016