Near-infrared scattered light properties of the HR 4796 A dust ring. A measured scattering phase function from 13.6° to 166.6°

$\textit{Context}$. HR 4796 A is surrounded by a debris disc, observed in scattered light as an inclined ring with a high surface brightness. Past observations have raised several questions. First, a strong brightness asymmetry detected in polarised reflected light has recently challenged our understanding of scattering by the dust particles in this system. Secondly, the morphology of the ring strongly suggests the presence of planets, although no planets have been detected to date. $\textit{Aims}$. We aim here at measuring with high accuracy the morphology and photometry of the ring in scattered light, in order to derive the phase function of the dust and constrain its near-infrared spectral properties. We also want to constrain the presence of planets and set improved constraints on the origin of the observed ring morphology. $\textit{Methods}$. We obtained high-angular resolution coronagraphic images of the circumstellar environment around HR 4796 A with VLT/SPHERE during the commissioning of the instrument in May 2014 and during guaranteed-time observations in February 2015. The observations reveal for the first time the entire ring of dust, including the semi-minor axis that was previously hidden either behind the coronagraphic spot or in the speckle noise. $\textit{Results}$. We determine empirically the scattering phase function of the dust in the H band from 13.6° to 166.6°. It shows a prominent peak of forward scattering, never detected before, for scattering angles below 30°. We analyse the reflectance spectra of the disc from the 0.95 μm to 1.6 μm, confirming the red colour of the dust, and derive detection limits on the presence of planetary mass objects. $\textit{Conclusions}$. We confirm which side of the disc is inclined towards the Earth. The analysis of the phase function, especially below 45°, suggests that the dust population is dominated by particles much larger than the observation wavelength, of about 20 μm. Compact Mie grains of this size are incompatible with the spectral energy distribution of the disc, however the observed rise in scattering efficiency beyond 50° points towards aggregates which could reconcile both observables. We do not detect companions orbiting the star, but our high-contrast observations provide the most stringent constraints yet on the presence of planets responsible for the morphology of the dust.J.M. acknowledges financial support from the ESO fellowship programme. A.M.L. acknowledges the support from the ANR blanche GIPSE (ANR-14-CE33-0018) and the Labex OSUG. L.M. acknowledges support by STFC and ESO through graduate studentships and by the European Union through ERC grant number 279973. We would like to thank ESO staff and technical operators at the Paranal Observatory. We thank M. Meyer and D. Rouan for their valueable suggestions and comments during the review by the SPHERE internal board. We thank P. Delorme and E. Lagadec (SPHERE Data Center) for their work during the data reduction process. We thank V. Faramaz for the discussion on the eccentricity of the disc. SPHERE is an instrument designed and built by a consortium consisting of IPAG (Grenoble, France), MPIA (Heidelberg, Germany), LAM (Marseille, France), LESIA (Paris, France), Laboratoire Lagrange (Nice, France), INAF – Osservatorio di Padova (Italy), Observatoire de Genève (Switzerland), ETH Zurich (Switzerland), NOVA (Netherlands), ONERA (France) and ASTRON (Netherlands) in collaboration with ESO. SPHERE was funded by ESO, with additional contributions from CNRS (France), MPIA (Germany), INAF (Italy), FINES (Switzerland) and NOVA (Netherlands). SPHERE also received funding from the European Commission Sixth and Seventh Framework Programmes as part of the Optical Infrared Coordination Network for Astronomy (OPTICON) under grant number RII3-Ct-2004-001566 for FP6 (2004–2008), grant number 226604 for FP7 (2009–2012) and grant number 312430 for FP7 (2013–2016)

Testing giant planet predictions in the transitional disk of SAO206462 using deep VLT/SPHERE imaging

The SAO206462 disk is one of the few known transitional disks showing asymmetric features in scattered light and thermal emission. Giant planets in formation were suggested for accounting for the disk features. We present deep SPHERE images of the disk. The spiral arms and the inner ring are revealed without the need for image post-processing. We also place deep constraints on putative planets

SHINE, SPHERE High-contrast ImagiNg survey for Exoplanets

The SHINE survey for SPHERE High-contrast ImagiNg survey for Exoplanets, is a large direct imaging near-infrared survey of 400-600 young, nearby stars carried out in the context of the SPHERE consortium Guaranteed Time Observations representing 200 nights spread between 2015 and 2020. Our scientific goals are to characterize known systems with substellar companions (architecture, orbit, stability, luminosity, atmosphere), to search for new planet and brown dwarf systems using SPHERE’s unprecedented performances, finally to determine the occurrence and orbital and mass function properties of the wide-orbit giant planet and brown dwarf populations as a function of the stellar host mass and age. In this talk, after summarizing the SHINE strategy and current performances after almost 3 years of operation, I will review the breakthrough results obtained so far including the discoveries of new exoplanet/BD companions and disks, the study of the architecture and stability of young planet/brown dwarf systems, and finally the fine characterization of the physical properties and atmospheres of the coolest substellar companions imaged to date

The SPHERE science capabilities for the study of young brown dwarfs and giant exoplanets

The VLT planet finder SPHERE saw first light in early May 2014 and was successfully commissionned during four runs spanning from May to October 2014. During the commissioning, we observed the two young systems of PZ Tel and HD1160 with several imaging and spectroscopic modes. We will discuss the spectral and physical properties of the companions PZ Tel B and HD1160 BC, the orbital parameters of PZ Tel B, and constraints on putative additional companions based on these new data. We will use these results to outline the new science capabilities offered by SPHERE for the study of young brown dwarfs and giant exoplanets, from high-contrast imaging capabilities at optical wavelengths (500-900 nm) to high signal-to-noise spectroscopy in the near-infrared domain (0.95-2.3 μm) from low resolutions (∼30-50) to medium resolutions (∼350)

Multiple rings in the transition disk and companion candidates around RX J1615.3-3255 High contrast imaging with VLT/SPHERE

International audienceContext. The effects of a planet sculpting the disk from which it formed are most likely to be found in disks that are in transition between being classical protoplanetary and debris disks. Recent direct imaging of transition disks has revealed structures such as dust rings, gaps, and spiral arms, but an unambiguous link between these structures and sculpting planets is yet to be found. Aims. We aim to find signs of ongoing planet-disk interaction and study the distribution of small grains at the surface of the transition disk around RXJ1615.3-3255 (RX J1615). Methods. We observed RXJ1615 with VLT/SPHERE. From these observations, we obtained polarimetric imaging with ZIMPOL (R'-band) and IRDIS (J), and IRDIS (H2H3) dual-band imaging with simultaneous spatially resolved spectra with the IFS (YJ). Results. We image the disk for the first time in scattered light and detect two arcs, two rings, a gap and an inner disk with marginal evidence for an inner cavity. The shapes of the arcs suggest that they are probably segments of full rings. Ellipse fitting for the two rings and inner disk yield a disk inclination i = 47 +/- 2 degrees and find semi-major axes of 1.50 +/- 0.01 `' (278 au), 1.06 +/- 0.01 `' (196 au) and 0.30 +/- 0.01 `' (56 au), respectively. We determine the scattering surface height above the midplane, based on the projected ring center offsets. Nine point sources are detected between 2.1 `' and 8.0 `' separation and considered as companion candidates. With NACO data we recover four of the nine point sources, which we determine to be not co-moving, and therefore unbound to the system. Conclusions. We present the first detection of the transition disk of RXJ1615 in scattered light. The height of the rings indicate limited flaring of the disk surface, which enables partial self-shadowing in the disk. The outermost arc either traces the bottom of the disk or it is another ring with semi-major axis greater than or similar to 2.35 `' (435 au). We explore both scenarios, extrapolating the complete shape of the feature, which will allow us to distinguish between the two in future observations. The most attractive scenario, where the arc traces the bottom of the outer ring, requires the disk to be truncated at r approximate to 360 au. If the closest companion candidate is indeed orbiting the disk at 540 au, then it would be the most likely cause for such truncation. This companion candidate, as well as the remaining four, all require follow up observations to determine if they are bound to the system