The system of fourplanets discovered around the intermediate-mass star HR8799 offers a unique opportunity to test planet formation theories at large orbital radii and to probe the physics and ...chemistry at play in the atmospheres of self-luminous young (~30 Myr) planets. In this paper (Paper IV), we aim to use these spectra and available photometry to determine how they compare to known objects, what the planet physical properties are, and how their atmospheres work. We compare the available spectra, photometry, and spectral energy distribution (SED) of the planets to field dwarfs and young companions. Our empirical analysis and atmospheric modelling show that an enhanced content in dust and decreased CIA of H2 is certainly responsible for the deviation of the properties of the planet with respect to field dwarfs. The analysis suggests in addition that HR8799c and b have later spectral types than the two other planets, and therefore could both have lower masses.
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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.
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Context.
β
Pictoris is arguably one of the most studied stellar systems outside of our own. Some 30 yr of observations have revealed a highly-structured circumstellar disk, with rings, belts, and a ...giant planet:
β
Pictoris b. However very little is known about how this system came into being.
Aims.
Our objective is to estimate the C/O ratio in the atmosphere of
β
Pictoris b and obtain an estimate of the dynamical mass of the planet, as well as to refine its orbital parameters using high-precision astrometry.
Methods.
We used the GRAVITY instrument with the four 8.2 m telescopes of the Very Large Telescope Interferometer to obtain
K
-band spectro-interferometric data on
β
Pic b. We extracted a medium resolution (
R
= 500)
K
-band spectrum of the planet and a high-precision astrometric position. We estimated the planetary C/O ratio using two different approaches (forward modeling and free retrieval) from two different codes (ExoREM and petitRADTRANS, respectively). Finally, we used a simplified model of two formation scenarios (gravitational collapse and core-accretion) to determine which can best explain the measured C/O ratio.
Results.
Our new astrometry disfavors a circular orbit for
β
Pic b (
e
= 0.15
−0.04
+0.05
). Combined with previous results and with H
IPPARCOS
/
Gaia
measurements, this astrometry points to a planet mass of
M
= 12.7 ± 2.2
M
Jup
. This value is compatible with the mass derived with the free-retrieval code petitRADTRANS using spectral data only. The forward modeling and free-retrieval approches yield very similar results regarding the atmosphere of
β
Pic b. In particular, the C/O ratios derived with the two codes are identical (0.43 ± 0.05 vs. 0.43
−0.03
+0.04
). We argue that if the stellar C/O in
β
Pic is Solar, then this combination of a very high mass and a low C/O ratio for the planet suggests a formation through core-accretion, with strong planetesimal enrichment.
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The SpHere INfrared Exoplanet (SHINE) project is a 500-star survey performed with SPHERE on the Very Large Telescope for the purpose of directly detecting new substellar companions and understanding ...their formation and early evolution. Here we present an initial statistical analysis for a subsample of 150 stars spanning spectral types from B to M that are representative of the full SHINE sample. Our goal is to constrain the frequency of substellar companions with masses between 1 and 75
M
Jup
and semimajor axes between 5 and 300 au. For this purpose, we adopt detection limits as a function of angular separation from the survey data for all stars converted into mass and projected orbital separation using the BEX-COND-hot evolutionary tracks and known distance to each system. Based on the results obtained for each star and on the 13 detections in the sample, we use a Markov chain Monte Carlo tool to compare our observations to two different types of models. The first is a parametric model based on observational constraints, and the second type are numerical models that combine advanced core accretion and gravitational instability planet population synthesis. Using the parametric model, we show that the frequencies of systems with at least one substellar companion are 23.0
−9.7
+13.5
, 5.8
−2.8
+4.7
, and 12.6
−7.1
+12.9
% for BA, FGK, and M stars, respectively. We also demonstrate that a planet-like formation pathway probably dominates the mass range from 1–75
M
Jup
for companions around BA stars, while for M dwarfs, brown dwarf binaries dominate detections. In contrast, a combination of binary star-like and planet-like formation is required to best fit the observations for FGK stars. Using our population model and restricting our sample to FGK stars, we derive a frequency of 5.7
−2.8
+3.8
%, consistent with predictions from the parametric model. More generally, the frequency values that we derive are in excellent agreement with values obtained in previous studies.
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Context. High-contrast instruments like SPHERE (Spectro- Polarimetric High-contrast Exoplanet REsearch) enable spatial resolution of young planetary systems and allow us to study the connection ...between planets and the dust contained in debris discs by the gravitational influence a planet can have on its environment. Aims. We present new observations of the edge-on debris disc around HD 15115 (F star at 48.2 pc) obtained in the near-IR. We search for observational evidence for a second inner planetesimal ring in the system. Methods. We obtained total intensity and polarimetric data in the broad bands J and H and processed the data with differential imaging techniques achieving an angular resolution of about 40 mas. A grid of models describing the spatial distribution of the grains in the disc is generated to constrain the geometric parameters of the disc and to explore the presence of a second belt. We perform a photometric analysis of the data and compare disc brightness in two bands in scattered and in polarized light. Results. We observe an axisymmetric planetesimal belt with a radius of ~2′′, an inclination of 85.8° ± 0.7° and position angle of 278.9° ± 0.1°. The photometric analysis shows that the west side is ~2.5 times brighter in total intensity than the east side in both bands, while for polarized light in the J band this ratio is only 1.25. We also find that the J–H colour of the disc appears to be red for the radial separations r ≲ 2′′ and is getting bluer for the larger separations. The maximum polarization fraction is 15–20% at r ~ 2.5′′. The polarized intensity image shows some structural features inside the belt which can be interpreted as an additional inner belt. Conclusions. The apparent change of disc colour from red to blue with an increasing radial separation from the star could be explained by the decreasing average grain size with distance. The presence of an inner belt slightly inclined with respect to the main planetesimal belt is suspected from the data but the analysis and modelling presented here cannot establish a firm conclusion due to the faintness of the disc and its high inclination.
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The young systemsPZ Tel and HD 1160, hosting known low-mass companions, were observed during the commissioning of the new planet finder of the Very Large Telescope (VLT) SPHERE with several imaging ...and spectroscopic modes. We aim to refine the physical properties and architecture of both systems. We use SPHERE commissioning data and dedicated Rapid Eye Mount (REM) observations, as well as literature and unpublished data from VLT/SINFONI, VLT/NaCo, Gemini/NICI, and Keck/NIRC2. We derive new photometry and confirm the short-term (P = 0.94 d) photometric variability of the star PZ Tel A with values of 0.14 and 0.06 mag at optical and near-infrared wavelengths, respectively. SPHERE opens new horizons in the study of young brown dwarfs and giant exoplanets using direct imaging thanks to high-contrast imaging capabilities at optical and near-infrared wavelengths, as well as high signal-to-noise spectroscopy in the near-infrared domain from low resolutions (R ~ 30-50) to medium resolutions (R ~ 350).
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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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Abstract
We present observations of the Herbig Ae star HD 169142 with the VLT/SPHERE instruments InfraRed Dual-band Imager and Spectrograph (IRDIS) (K1K2 and H2H3 bands) and the Integral Field ...Spectrograph (IFS) (Y, J and H bands). We detect several bright blobs at ∼180 mas separation from the star, and a faint arc-like structure in the IFS data. Our reference differential imaging (RDI) data analysis also finds a bright ring at the same separation. We show, using a simulation based on polarized light data, that these blobs are actually part of the ring at 180 mas. These results demonstrate that the earlier detections of blobs in the H and KS bands at these separations in Biller et al. as potential planet/substellar companions are actually tracing a bright ring with a Keplerian motion. Moreover, we detect in the images an additional bright structure at ∼93 mas separation and position angle of 355°, at a location very close to previous detections. It appears point-like in the YJ and K bands but is more extended in the H band. We also marginally detect an inner ring in the RDI data at ∼100 mas. Follow-up observations are necessary to confirm the detection and the nature of this source and structure.
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′′.
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Context. HD 106906AB is the only young binary system so far around which a planet has been imaged and a debris disk has been shown to exist, thanks to a strong IR excess. As such, it represents a ...unique opportunity for studying the dynamics of young planetary systems. Aims. We aim at further investigating the close (tens of au scales) environment of the HD 106906AB system. Methods. We used the extreme adaptive-optics-fed, high-contrast imager SPHERE that has recently been installed on the VLT to observe HD 106906. Both the IRDIS imager and the Integral Field Spectrometer were used. Results. We discovered a highly inclined, ring-like disk at a distance of 65 au from the star. The disk shows a strong brightness asymmetry with respect to its semi-major axis. It shows a smooth outer edge, compatible with ejection of small grains by the stellar radiation pressure. We show furthermore that the planet’s projected position is significantly above the PA of the disk. Given the determined disk inclination, it is not excluded, however, that the planet could still orbit within the disk plane if at a large separation (2000−3000 au). We identified several additional point sources in the SPHERE/IRDIS field of view that appear to be background objects. We compare this system with other debris disks sharing similarities, and we briefly discuss the present results in the framework of dynamical evolution.
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