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We present scattered light images of the TW Hya disk performed with SPHERE in PDI mode at 0.63, 0.79, 1.24 and 1.62 µm. We also present H2/H3-band ADI observations. Three distinct radial depressions in the polarized intensity distribution are seen, around ≈ 85, ≈ 21, and 6 au 1 . The overall intensity distribution has a high degree of azimuthal symmetry; the disk is somewhat brighter than average towards the South and darker towards the North-West. The ADI observations yielded no signifiant detection of point sources in the disk.Our observations have a linear spatial resolution of 1 to 2 au, similar to that of recent ALMA dust continuum observations. The sub-micron sized dust grains that dominate the light scattering in the disk surface are strongly coupled to the gas. We created a radiative transfer disk model with self-consistent temperature and vertical structure iteration and including grain size-dependent dust settling. This method may provide independent constraints on the gas distribution at higher spatial resolution than is feasible with ALMA gas line observations.We find that the gas surface density in the "gaps" is reduced by ≈ 50% to ≈ 80% relative to an unperturbed model. Should embedded planets be responsible for carving the gaps then their masses are at most a few 10 M ⊕ . The observed gaps are wider, with shallower flanks, than expected for planetdisk interaction with such low-mass planets. If forming planetary bodies have undergone collapse and are in the "detached phase", then they may be directly observable with future facilities such as METIS at the E-ELT. 1 Throughout this work we have assumed a distance of 54 pc to TW Hya. This is ≈ 10% less than the new GAIA distance of 59.5 +0.96 −0.93 pc (Gaia Collaboration et al. 2016). We discuss the implications of the new, somewhat larger distance in Section 5.5.3.

We have observed the protoplanetary disk of the well-known young Herbig star HD 142527 using ZIMPOL Polarimetric Differential Imaging with the VBB (Very Broad Band, ∼ 600-900nm) filter. We obtained two datasets in May 2015 and March 2016. Our data allow us to explore dust scattering around the star down to a radius of ∼0.025 (∼ 4au). The well-known outer disk is clearly detected, at higher resolution than before, and shows previously unknown sub-structures, including spirals going inwards into the cavity. Close to the star, dust scattering is detected at high signal-to-noise ratio, but it is unclear whether the signal represents the inner disk, which has been linked to the two prominent local minima in the scattering of the outer disk, interpreted as shadows. An interpretation of an inclined inner disk combined with a dust halo is compatible with both our and previous observations, but other arrangements of the dust cannot be ruled out. Dust scattering is also present within the large gap between ∼30 and ∼140au. The comparison of the two datasets suggests rapid evolution of the inner regions of the disk, potentially driven by the interaction with the close-in M-dwarf companion, around which no polarimetric signal is detected.

Context. Debris disks are observed around 10 to 20 % of FGK main-sequence stars as infrared excess emission. They are important signposts for the presence of colliding planetesimals and therefore provide important information about the evolution of planetary systems. Direct imaging of such disks reveals their geometric structure and constrains their dust-particle properties. Aims. We present observations of the known edge-on debris disk around HIP 79977 (HD 146897) taken with the ZIMPOL differential polarimeter of the SPHERE instrument. We measure the observed polarization signal and investigate the diagnostic potential of such data with model simulations.Methods. SPHERE-ZIMPOL polarimetric data of the 15 Myr-old F star HIP 79977 (Upper Sco, 123 pc) were taken in the Very Broad Band (VBB) filter (λ c = 735 nm, ∆λ = 290 nm) with a spatial resolution of about 25 mas. Imaging polarimetry efficiently suppresses the residual speckle noise from the AO system and provides a differential signal with relatively small systematic measuring uncertainties. We measure the polarization flux along and perpendicular to the disk spine of the highly inclined disk for projected separations between 0.2 (25 AU) and 1.6 (200 AU). We perform model calculations for the polarized flux of an optically thin debris disk which are used to determine or constrain the disk parameters of HIP 79977. Results. We measure a polarized flux contrast ratio for the disk of (F pol ) disk /F * = (5.5 ± 0.9) · 10 −4 in the VBB filter. The surface brightness of the polarized flux reaches a maximum of SB max = 16.2 mag arcsec −2 at a separation of 0.2 − 0.5 along the disk spine with a maximum surface brightness contrast of 7.64 mag arcsec −2 . The polarized flux has a minimum near the star < 0.2 because no or only little polarization is produced by forward or backward scattering in the disk section lying in front of or behind the star. The width of the disk perpendicular to the spine shows a systematic increase in FWHM from 0.1 (12 AU) to 0.3 − 0.5 , when going from a separation of 0.2 to > 1 . This can be explained by a radial blow-out of small grains. The data are modelled as a circular dust belt with a well defined disk inclination i = 85(±1.5) • and a radius between r 0 = 60 and 90 AU. The radial density dependence is described by (r/r 0 ) α with a steep (positive) power law index α = 5 inside r 0 and a more shallow (negative) index α = −2.5 outside r 0 . The scattering asymmetry factor lies between g = 0.2 and 0.6 (forward scattering) adopting a scattering-angle dependence for the fractional polarization such as that for Rayleigh scattering. Conclusions. Polarimetric imaging with SPHERE-ZIMPOL of the edge-on debris disk around HIP 79977 provides accurate profiles for the polarized flux. Our data are qualitatively very similar to the case of AU Mic and they confirm that edge-on debris disks have a polarization minimum at a position near the star and a maximum near the projected separation of the main debris belt. The comparison of the polarized flux contr...

We present observations of the young multiple system UX Tauri to look for circumstellar disks and for signs of dynamical interactions. We obtained SPHERE/IRDIS deep differential polarization images in the J and H bands. We also used ALMA archival CO data. Large extended spirals are well detected in scattered light coming out of the disk of UX Tau A. The southern spiral forms a bridge between UX Tau A and C. These spirals, including the bridge connecting the two stars, all have a CO (3–2) counterpart seen by ALMA. The disk of UX Tau C is detected in scattered light. It is much smaller than the disk of UX Tau A and has a major axis along a different position angle, suggesting a misalignment. We performed PHANTOM SPH hydrodynamical models to interpret the data. The scattered light spirals, CO emission spirals and velocity patterns of the rotating disks, and the compactness of the disk of UX Tau C all point to a scenario in which UX Tau A has been perturbed very recently (∼1000 years) by the close passage of UX Tau C.

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The Planet Finder instrument for ESO's VLT telescope, scheduled for first light in 2010, aims to detect giant extra-solar planets in the vicinity of bright stars and to characterise the objects found through spectroscopic and polarimetric observations. The observations will be done both within the Y, J, H and Ks atmospheric windows (~0.95 -2.32µm) by the aid of a dual imaging camera (IRDIS) and an integral field spectrograph (IFS), and in the visible using a fastmodulation polarization camera (ZIMPOL). The instrument employs an extreme-AO turbulence compensation system, focal plane tip-tilt correction, and interferential coronagraphs. We describe briefly the science goals of the instrument and deduce the top-level requirements. The system architecture is presented, including brief descriptions of each of the main sub-systems. Expected performance is described in terms of end-to-end simulations, and a semi-analytic performance-estimation tool for system-level sensitivity analysis is presented.

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