LkCa 15 hosts a pre-transitional disk as well as at least one accreting protoplanet orbiting in its gap. Previous disk observations have focused mainly on the outer disk, which is cleared inward of ...~50 au. The planet candidates, on the other hand, reside at orbital radii around 15 au, where disk observations have been unreliable until recently. Here, we present new J-band imaging polarimetry of LkCa 15 with SPHERE IRDIS, yielding the most accurate and detailed scattered-light images of the disk to date down to the planet-hosting inner regions. We find what appear to be persistent asymmetric structures in the scattering material at the location of the planet candidates, which could be responsible at least for parts of the signals measured with sparse-aperture masking. These images further allow us to trace the gap edge in scattered light at all position angles and search the inner and outer disks for morphological substructure. The outer disk appears smooth with slight azimuthal variations in polarized surface brightness, which may be due to shadowing from the inner disk or a two-peaked polarized phase function. We find that the near-side gap edge revealed by polarimetry matches the sharp crescent seen in previous ADI imaging very well. Finally, the ratio of polarized disk to stellar flux is more than six times larger in the J-band than in the RI bands.
Context. 51 Eridani b is an exoplanet around a young (20 Myr) nearby (29.4 pc) F0-type star, which was recently discovered by direct imaging. It is one of the closest direct imaging planets in ...angular and physical separation (~0.5′′, ~13 au) and is well suited for spectroscopic analysis using integral field spectrographs. Aims. We aim to refine the atmospheric properties of the known giant planet and to constrain the architecture of the system further by searching for additional companions. Methods. We used the extreme adaptive optics instrument SPHERE at the Very Large Telescope (VLT) to obtain simultaneous dual-band imaging with IRDIS and integral field spectra with IFS, extending the spectral coverage of the planet to the complete Y- to H-band range and providing additional photometry in the K12-bands (2.11, 2.25 μm). The object is compared to other known cool and peculiar dwarfs. The posterior probability distributions for parameters of cloudy and clear atmospheric models are explored using MCMC. We verified our methods by determining atmospheric parameters for the two benchmark brown dwarfs Gl 570D and HD 3651B. We used archival VLT-NACO (L′) Sparse Aperture Masking data to probe the innermost region for additional companions. Results. We present the first spectrophotometric measurements in the Y and K bands for the planet and revise its J-band flux to values 40% fainter than previous measurements. Cloudy models with uniform cloud coverage provide a good match to the data. We derive the temperature, radius, surface gravity, metallicity, and cloud sedimentation parameter fsed. We find that the atmosphere is highly super-solar (Fe/H = 1.0 ± 0.1 dex), and the low \hbox{${f_{\rm sed} = 1.26^{+0.36}_{-0.29}}$}fsed=1.26-0.29+0.36 value is indicative of a vertically extended, optically thick cloud cover with small sized particles. The model radius and surface gravity estimates suggest higher planetary masses of \hbox{${M_\mathrm{gravity} = 9.1^{+4.9}_{-3.3} \, {M}_\mathrm{J}}$}Mgravity=9.1-3.3+4.9 MJ. The evolutionary model only provides a lower mass limit of > 2 MJ (for pure hot-start). The cold-start model cannot explain the luminosity of the planet. The SPHERE and NACO/SAM detection limits probe the 51 Eri system at solar system scales and exclude brown-dwarf companions more massive than 20 MJ beyond separations of ~2.5 au and giant planets more massive than 2 MJ beyond 9 au.
Context. Debris disks correspond to the final evolutionary stage of circumstellar disks around young stars. Gas-deprived structures seen in debris disks are normally, but not always, attributed to ...dynamical interactions in young planetary systems. Aims. The debris disk of HIP 73145 has been detected in scattered light in the near-IR, and at far-IR wavelengths before, but no substructure has been seen so far. Detection of such substructures in combination with detailed modeling can hint at the presence of perturbing planetary bodies, or reveal other mechanisms acting to replenish gas and dust reservoirs and forming structures such as spirals or rings. Methods. We obtained multiwavelength images with SPHERE in the near-IR in the H2 and H3 bands with the IRDIS camera and a 0.95−1.35 μm spectral cube with the IFS. Data were acquired in pupil-tracking mode, thus allowing for angular differential imaging. The SPHERE standard suite of angular differential imaging algorithms was applied. ALMA Band 6 observations complement the SPHERE data. Results. We detect a bright ring of scattered light plus some secondary structures inside, at least one of them forming a secondary, concentric ring with the first. This is the first detection of this disk in total-intensity scattered light. A second object is detected in the field at high contrast but concluded to be a background star. Forward modeling yields information on the primary parameters of the disk and confirms that the detected substructures are not due to the data analysis approach, which sometimes leads to spurious structures. Conclusions. We detect a series of concentric rings in the disk around HIP 73145. This is one of the rare cases where multiple components are necessary to fit the SED and are also detected in scattered light. The presence of such ring structures somewhat questions the nature of the object as a pure debris disk, but the gas and dust content would presumably offer sufficient explanations for such structures to form.
Context. The SAO 206462 (HD 135344B) disk is one of the few known transitional disks showing asymmetric features in scattered light and thermal emission. Near-infrared scattered-light images revealed ...two bright outer spiral arms and an inner cavity depleted in dust. Giant protoplanets have been proposed to account for the disk morphology. Aims. We aim to search for giant planets responsible for the disk features and, in the case of non-detection, to constrain recent planet predictions using the data detection limits. Methods. We obtained new high-contrast and high-resolution total intensity images of the target spanning the Y to the K bands (0.95–2.3 μm) using the VLT/SPHERE near-infrared camera and integral field spectrometer. Results. The spiral arms and the outer cavity edge are revealed at high resolutions and sensitivities without the need for aggressive image post-processing techniques, which introduce photometric biases. We do not detect any close-in companions. For the derivation of the detection limits on putative giant planets embedded in the disk, we show that the knowledge of the disk aspect ratio and viscosity is critical for the estimation of the attenuation of a planet signal by the protoplanetary dust because of the gaps that these putative planets may open. Given assumptions on these parameters, the mass limits can vary from ~2–5 to ~4–7 Jupiter masses at separations beyond the disk spiral arms. The SPHERE detection limits are more stringent than those derived from archival NaCo/L′ data and provide new constraints on a few recent predictions of massive planets (4–15 MJ) based on the spiral density wave theory. The SPHERE and ALMA data do not favor the hypotheses on massive giant planets in the outer disk (beyond 0.6′′). There could still be low-mass planets in the outer disk and/or planets inside the cavity.
HIP 65426 b is a recently discovered exoplanet imaged during the course of the SPHERE-SHINE survey. Here we present new L′ and M′ observations of the planet from the NACO instrument at the VLT from ...the NACO-ISPY survey, as well as a new Y –H spectrum and K-band photometry from SPHERE-SHINE. Using these data, we confirm the nature of the companion as a warm, dusty planet with a mid-L spectral type. From comparison of its SED with the BT-Settl atmospheric models, we derive a best-fit effective temperature of Teff = 1618 ± 7 K, surface gravity log g = 3.78−0.03+0.04 $\log g\,{=}\,3.78^{+0.04}_{-0.03}$logg = 3.78−0.03+0.04 and radius R = 1.17 ± 0.04RJ (statistical uncertainties only). Using the DUSTY and COND isochrones we estimate a mass of 8 ± 1MJ. Combining the astrometric measurements from our new datasets and from the literature, we show the first indications of orbital motion of the companion (2.6σ significance)and derive preliminary orbital constraints. We find a highly inclined orbit ( i = 1.07−10+13 $i\,{=}\,107^{+13}_{-10}$i = 107−10+13 deg) with an orbital period of 800−400+1200 $800^{+1200}_{-400}$800−400+1200 yr. We also report SPHERE sparse aperture masking observations that investigate the possibility that HIP 65426 b was scattered onto its current orbit by an additional companion at a smaller orbital separation. From this data we rule out the presence of brown dwarf companions with masses greater than 16 MJ at separations larger than 3 AU, significantly narrowing the parameter space for such a companion.
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 (λc = 735 nm, Δλ = 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 (Fpol)disk/F∗ = (5.5 ± 0.9) × 10-4 in the VBB filter. The surface brightness of the polarized flux reaches a maximum of SBmax = 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 r0 = 60 and 90 AU. The radial density dependence is described by (r/r0)α with a steep (positive) power law index α = 5 inside r0 and a more shallow (negative) index α = −2.5 outside r0. 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 contrast ratio (Fpol)disk/F∗ with the fractional infrared excess provides strong constraints on the scattering albedo of the dust.
Context. Crucial information on the mass accretion-ejection connection in young stars can be obtained from high spatial resolution images of jets in sources with known recurrent accretion outbursts. ...Aims. Using the VLT/SPHERE ZIMPOL instrument, we observed the young binary Z CMa that is composed of a Herbig Be star and a FUor object, both driving a jet. We aim to analyse the structure of the two jets, their relation with the properties of the driving sources, and their connection with previous accretion events observed in this target. Methods. We obtained optical images in the Hα and O i 6300 Å lines at the unprecedented angular resolution of ~0.03 arcsec, on which we have performed both continuum subtraction and deconvolution, thereby deriving results that are consistent with each other. Results. Our images reveal extended emission from both sources: a fairly compact and poorly collimated emission SW of the Herbig component and an extended collimated and precessing jet from the FUor component. The compact emission from the Herbig star is compatible with a wide-angle wind and is possibly connected to the recent outburst events shown by this component. The FUor jet is traced down to 70 mas (80 AU) from the source and is highly collimated with a width of 26−48 AU at distances 100−200 AU, which is similar to the width of jets from T Tauri stars. This strongly suggests that the same magneto-centrifugal jet-launching mechanism also operates in FUors. The observed jet wiggle can be modelled as originating from an orbital motion with a period of 4.2 yr around an unseen companion with mass between 0.48 and 1 M⊙. The jet mass loss rate Ṁjet was derived from the O i luminosity and comprises of between 1 × 10-8 and 1 × 10-6M⊙ yr-1. This is the first direct Ṁjet measurement from a jet in a FUor. If we assume previous mass accretion rate estimates obtained through modelling of the accretion disk, the derived range of Ṁjet would imply a very low mass-ejection efficiency (Ṁjet/Ṁacc≲ 0.02), which is lower than that typical of T Tauri stars.
Debris disks are usually detected through the infrared excess over the photospheric level of their host star. The most favorable stars for disk detection are those with spectral types between A and ...K, while the statistics for debris disks detected around low-mass M-type stars is very low, either because they are rare or because they are more difficult to detect. Terrestrial planets, on the other hand, may be common around M-type stars. Here, we report on the discovery of an extended (likely) debris disk around the M-dwarf GSC 07396−00759. The star is a wide companion of the close accreting binary V4046 Sgr. The system probably is a member of the β Pictoris Moving Group. We resolve the disk in scattered light, exploiting high-contrast, high-resolution imagery with the two near-infrared subsystems of the VLT/SPHERE instrument, operating in the Y J bands and the H2H3 doublet. The disk is clearly detected up to 1.5′′ (~110 au) from the star and appears as a ring, with an inclination i ~ 83°, and a peak density position at ~70 au. The spatial extension of the disk suggests that the dust dynamics is affected by a strong stellar wind, showing similarities with the AU Mic system that has also been resolved with SPHERE. The images show faint asymmetric structures at the widest separation in the northwest side. We also set an upper limit for the presence of giant planets to 2 MJ. Finally, we note that the 2 resolved disks around M-type stars of 30 such stars observed with SPHERE are viewed close to edge-on, suggesting that a significant population of debris disks around M dwarfs could remain undetected because of an unfavorable orientation.
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. 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. 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). 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 Uφ images, with a Uφ/Qφ 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. 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 Mjup between 0.̋1 and 0.̋3. The detection limit decreases to ~2 Mjup for 0.̋3 to 4.0′′.
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.
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