Abstract
Context. Transition disks are considered sites of ongoing planet formation, and their dust and gas distributions could be signposts of embedded planets. The transition disk around the T Tauri star RY Lup has an inner dust cavity and displays a strong silicate emission feature. Aims. Using high-resolution imaging we study the disk geometry, including non-axisymmetric features, and its surface dust grain, to gain a better understanding of the disk evolutionary process. Moreover, we search for companion candidates, possibly connected to the disk. Methods. We obtained high-contrast and high angular resolution data in the near-infrared with the VLT/SPHERE extreme adaptive optics instrument whose goal is to study the planet formation by detecting and characterizing these planets and their formation environments through direct imaging. We performed polarimetric imaging of the RY Lup disk with IRDIS (at 1.6 μm), and obtained intensity images with the IRDIS dual-band imaging camera simultaneously with the IFS spectro-imager (0.9–1.3 μm). Results. We resolved for the first time the scattered light from the nearly edge-on circumstellar disk around RY Lup, at projected separations in the 100 au range. The shape of the disk and its sharp features are clearly detectable at wavelengths ranging from 0.9 to 1.6 μm. We show that the observed morphology can be interpreted as spiral arms in the disk. This interpretation is supported by in-depth numerical simulations. We also demonstrate that these features can be produced by one planet interacting with the disk. We also detect several point sources which are classified as probable background objects.
Highlights
High-resolution and high-contrast imaging capabilities provided by the new generation of adaptive optics based instruments such as the Spectro-Polarimeter High-contrast Exoplanet REsearch (SPHERE) instrument (Beuzit et al 2008) and the Gemini Planer Imager (GPI; Macintosh et al 2014) open the path to directly image new protoplanetary disks in scattered light
The analysis of the morphology of the detected disk primarily focuses on the IRDIS and IFS intensity images and IRDIS-DPI
The cADI IFS and IRDIS images are used to search for point-sources focusing on non-polarized companions because the intensity images reach higher contrast (Sect. 3.2)
Summary
High-resolution and high-contrast imaging capabilities provided by the new generation of adaptive optics based instruments such as the Spectro-Polarimeter High-contrast Exoplanet REsearch (SPHERE) instrument (Beuzit et al 2008) and the Gemini Planer Imager (GPI; Macintosh et al 2014) open the path to directly image new protoplanetary disks in scattered light. The intrinsic position angle of T Tauri star polarization is generally a function of both wavelength and time (Bastien 1981, 1985) These authors noticed remarkably large and rapid variations in both polarization and position angle in RY Lup. More recently, Manset et al (2009) has investigated these photometric and polarimetric variabilities using simultaneous BV polarimetric and UBV photometric observations. Recent ALMA high-resolution sub-mm observations of RY Lup in the 890 micron dust continuum (Ansdell et al 2016) provide a detailed map of the spatial distribution of large, mmsized dust, at a linear spatial resolution of 35 au They show a clear signature of an inner mm dust cavity with a diameter of 0.8 (60 au) and a clearly resolved dust ring. This is followed by detailed numerical modelling of the disk (Sect. 4)
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