| 1. |
- Keppler, M., et al.
(författare)
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Discovery of a planetary-mass companion within the gap of the transition disk around PDS 70
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 617
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Tidskriftsartikel (refereegranskat)abstract
- Context. Young circumstellar disks are the birthplaces of planets. Their study is of prime interest to understand the physical and chemical conditions under which planet formation takes place. Only very few detections of planet candidates within these disks exist, and most of them are currently suspected to be disk features.Aims. In this context, the transition disk around the young star PDS 70 is of particular interest, due to its large gap identified in previous observations, indicative of ongoing planet formation. We aim to search for the presence of an embedded young planet and search for disk structures that may be the result of disk-planet interactions and other evolutionary processes.Methods. We analyse new and archival near-infrared images of the transition disk PDS 70 obtained with the VLT/SPHERE, VLT/NaCo, and Gemini/NICI instruments in polarimetric differential imaging and angular differential imaging modes.Results. We detect a point source within the gap of the disk at about 195 mas (similar to 22 au) projected separation. The detection is confirmed at five different epochs, in three filter bands and using different instruments. The astrometry results in an object of bound nature, with high significance. The comparison of the measured magnitudes and colours to evolutionary tracks suggests that the detection is a companion of planetary mass. The luminosity of the detected object is consistent with that of an L-type dwarf, but its IR colours are redder, possibly indicating the presence of warm surrounding material. Further, we confirm the detection of a large gap of similar to 54 au in size within the disk in our scattered light images, and detect a signal from an inner disk component. We find that its spatial extent is very likely smaller than similar to 17 au in radius, and its position angle is consistent with that of the outer disk. The images of the outer disk show evidence of a complex azimuthal brightness distribution which is different at different wavelengths and may in part be explained by Rayleigh scattering from very small grains.Conclusions. The detection of a young protoplanet within the gap of the transition disk around PDS 70 opens the door to a so far observationally unexplored parameter space of planetary formation and evolution. Future observations of this system at different wavelengths and continuing astrometry will allow us to test theoretical predictions regarding planet-disk interactions, planetary atmospheres, and evolutionary models.
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| 2. |
- Glauser, A. M., et al.
(författare)
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Characterizing exoplanets in the visible and infrared: A spectrometer concept for the EChO space mission
- 2013
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Ingår i: Journal of Astronomical Instrumentation. - 2251-1725 .- 2251-1717. ; 2:1
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Tidskriftsartikel (refereegranskat)abstract
- Transit-spectroscopy of exoplanets is one of the key observational techniques used to characterize extrasolar planets and their atmospheres. The observational challenges of these measurements require dedicated instrumentation and only the space environment allows undisturbed access to earth-like atmospheric features such as water or carbon dioxide. Therefore, several exoplanet-specific space missions are currently being studied. One of them is EChO, the Exoplanet Characterization Observatory, which is part of ESA's Cosmic Vision 2015-2025 program, and which is one of four candidates for the M3 launch slot in 2024. In this paper we present the results of our assessment study of the EChO spectrometer, the only science instrument onboard this spacecraft. The instrument is a multi-channel all-reflective dispersive spectrometer, covering the wavelength range from 400 nm to 16μm simultaneously with a moderately low spectral resolution. We illustrate how the key technical challenge of the EChO mission - the high photometric stability - influences the choice of spectrometer concept and fundamentally drives the instrument design. First performance evaluations underline the suitability of the elaborated design solution for the needs of the EChO mission.
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| 3. |
- Weigelt, G., et al.
(författare)
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VLTI-MATISSE chromatic aperture-synthesis imaging of eta Carinae's stellar wind across the Br alpha line Periastron passage observations in February 2020
- 2021
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 652
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Tidskriftsartikel (refereegranskat)abstract
- Context. Eta Carinae is a highly eccentric, massive binary system (semimajor axis similar to 15.5 au) with powerful stellar winds and a phase-dependent wind-wind collision (WWC) zone. The primary star, eta Car A, is a luminous blue variable (LBV); the secondary, eta Car B, is a Wolf-Rayet or O star with a faster but less dense wind. Aperture-synthesis imaging allows us to study the mass loss from the enigmatic LBV eta Car. Understanding LBVs is a crucial step toward improving our knowledge about massive stars and their evolution. Aims. Our aim is to study the intensity distribution and kinematics of eta Car's WWC zone. Methods. Using the VLTI-MATISSE mid-infrared interferometry instrument, we perform Br alpha imaging of eta Car's distorted wind. Results. We present the first VLTI-MATISSE aperture-synthesis images of eta Car A's stellar windin several spectral channels distributed across the Br alpha 4.052 mu m line (spectral resolving power R similar to 960). Our observations were performed close to periastron passage in February 2020 (orbital phase similar to 14.0022). The reconstructed iso-velocity images show the dependence of the primary stellar wind on wavelength or line-of-sight (LOS) velocity with a spatial resolution of 6 mas (similar to 14 au). The radius of the faintest outer wind regions is similar to 26 mas (similar to 60 au). At several negative LOS velocities, the primary stellar wind is less extended to the northwest than in other directions. This asymmetry is most likely caused by the WWC. Therefore, we see both the velocity field of the undisturbed primary wind and the WWC cavity. In continuum spectral channels, the primary star wind is more compact than in line channels. A fit of the observed continuum visibilities with the visibilities of a stellar wind CMFGEN model (CMFGEN is an atmosphere code developed to model the spectra of a variety of objects) provides a full width at half maximum fit diameter of the primary stellar wind of 2.84 +/- 0.06 mas (6.54 +/- 0.14 au). We comparethe derived intensity distributions with the CMFGEN stellar wind model and hydrodynamic WWC models.
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| 4. |
- Asensio-Torres, R., et al.
(författare)
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Perturbers : SPHERE detection limits to planetary-mass companions in protoplanetary disks
- 2021
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 652
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Tidskriftsartikel (refereegranskat)abstract
- The detection of a wide range of substructures such as rings, cavities, and spirals has become a common outcome of high spatial resolution imaging of protoplanetary disks, both in the near-infrared scattered light and in the thermal millimetre continuum emission. The most frequent interpretation of their origin is the presence of planetary-mass companions perturbing the gas and dust distribution in the disk (perturbers), but so far the only bona fide detection has been the two giant planets carving the disk around PDS 70. Here, we present a sample of 15 protoplanetary disks showing substructures in SPHERE scattered-light images and a homogeneous derivation of planet detection limits in these systems. To obtain mass limits we rely on different post-formation luminosity models based on distinct formation conditions, which are critical in the first million years of evolution. We also estimate the mass of these perturbers through a Hill radius prescription and a comparison to ALMA data. Assuming that one single planet carves each substructure in scattered light, we find that more massive perturbers are needed to create gaps within cavities than rings, and that we might be close to a detection in the cavities of RX J1604.3-2130A, RX J1615.3-3255, Sz Cha, HD 135344B, and HD 34282. We reach typical mass limits in these cavities of 3–10 MJup. For planets in the gaps between rings, we find that the detection limits of SPHERE high-contrast imaging are about an order of magnitude away in mass, and that the gaps of PDS 66 and HD 97048 seem to be the most promising structures for planet searches. The proposed presence of massive planets causing spiral features in HD 135344B and HD 36112 are also within SPHERE’s reach assuming hot-start models. These results suggest that the current detection limits are able to detect hot-start planets in cavities, under the assumption that they are formed by a single perturber located at the centre of the cavity. More realistic planet mass constraints would help to clarify whether this is actually the case, which might indicate that perturbers are not the only way of creating substructures.
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| 5. |
- Chiavassa, A., et al.
(författare)
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The extended atmosphere and circumstellar environment of the cool evolved star VX Sagittarii as seen by MATISSE star
- 2022
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 658
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Tidskriftsartikel (refereegranskat)abstract
- Context. VX Sgr is a cool, evolved, and luminous red star whose stellar parameters are difficult to determine, which affects its classification.Aims. We aim to spatially resolve the photospheric extent as well as the circumstellar environment.Methods. We used interferometric observations obtained with the MATISSE instrument in the L (3-4 mu m), M (4.5-5 mu m), and N (8-13 mu m) bands. We reconstructed monochromatic images using the MIRA software. We used 3D radiation-hydrodynamics simulations carried out with (COBOLD)-B-5 and a uniform disc model to estimate the apparent diameter and interpret the stellar surface structures. Moreover, we employed the radiative transfer codes OPTIM3D and RADMC3D to compute the spectral energy distribution for the L, M, and N bands, respectively.Results. MATISSE observations unveil, for the first time, the morphology of VX Sgr across the L, M, and N bands. The reconstructed images show a complex morphology with brighter areas whose characteristics depend on the wavelength probed. We measured the angular diameter as a function of the wavelength and showed that the photospheric extent in the L and M bands depends on the opacity through the atmosphere. In addition to this, we also concluded that the observed photospheric inhomogeneities can be interpreted as convection-related surface structures. The comparison in the N band yielded a qualitative agreement between the N-band spectrum and simple dust radiative transfer simulations. However, it is not possible to firmly conclude on the interpretation of the current data because of the difficulty in constraing the model parameters using the limited accuracy of our absolute flux calibration.Conclusions. MATISSE observations and the derived reconstructed images unveil the appearance of VX Sgr's stellar surface and circumstellar environment across a very large spectral domain for the first time.
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| 6. |
- Cugno, G., et al.
(författare)
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A search for accreting young companions embedded in circumstellar disks High-contrast H alpha imaging with VLT/SPHERE
- 2019
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 622
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Tidskriftsartikel (refereegranskat)abstract
- Context. In recent years, our understanding of giant planet formation progressed substantially. There have even been detections of a few young protoplanet candidates still embedded in the circumstellar disks of their host stars. The exact physics that describes the accretion of material from the circumstellar disk onto the suspected circumplanetary disk and eventually onto the young, forming planet is still an open question.Aims. We seek to detect and quantify observables related to accretion processes occurring locally in circumstellar disks, which could be attributed to young forming planets. We focus on objects known to host protoplanet candidates and/or disk structures thought to be the result of interactions with planets.Methods. We analyzed observations of six young stars (age 3.5-10 Myr) and their surrounding environments with the SPHERE/ZIMPOL instrument on the Very Large Telescope (VLT) in the H alpha filter (656 nm) and a nearby continuum filter (644.9 nm). We applied several point spread function (PSF) subtraction techniques to reach the highest possible contrast near the primary star, specifically investigating regions where forming companions were claimed or have been suggested based on observed disk morphology.Results. We redetect the known accreting M-star companion HD142527 B with the highest published signal to noise to date in both H alpha and the continuum. We derive new astrometry (r = 62.8(-2.7)(+2.1)mas and PA = (98.7 +/- 1.8)degrees) and photometry (Delta N_Ha = 6.3-(+0.2)(0.3) mag, Delta B_Ha = 6.7 +/- 0.2 mag and Delta Cnt_Ha= 7.3(-0.2)(+0.3) mag) for the companion in agreement with previous studies, and estimate its mass accretion rate (M approximate to 1-2 x 10(-10) M-circle dot yr(-1)). A faint point-like source around HD135344 B (SA0206462) is also investigated, but a second deeper observation is required to reveal its nature. No other companions are detected. In the framework of our assumptions we estimate detection limits at the locations of companion candidates around HD100546, HD169142, and MWC 758 and calculate that processes involving Ha fluxes larger than similar to 8 x 10(-14)-10(-15) erg s(-1) cm(-2) (M > 10(-10)-10(-12) M-circle dot yr(-1)) can be excluded. Furthermore, flux upper limits of similar to 10(-14)-10(-15)erg s(-1) cm(-2) (M < 10(-11) -10(-12)M(circle dot )yr(-1)) are estimated within the gaps identified in the disks surrounding HD135344 B and TW Hya. The derived luminosity limits exclude H alpha signatures at levels similar to those previously detected for the accreting planet candidate LkCa15 b.
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| 7. |
- Pohl, A., et al.
(författare)
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New constraints on the disk characteristics and companion candidates around T Chamaeleontis with VLT/SPHERE
- 2017
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 605
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Tidskriftsartikel (refereegranskat)abstract
- 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 mu m) and ZIMPOL (0.5-0.9 mu m), and obtained intensity images from IRDIS dual-band imaging with simultaneous spectro-imaging with IFS (0.9-1.3 mu m).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 U-phi images, with a U-phi/Q(phi) 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 (similar to 30 au) in size, which is larger than previously thought. We derive a disk inclination of similar to 69 deg and PA of similar to 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 similar to 8.5 M-jup between 0.'' 1 and 0.'' 3. The detection limit decreases to similar to 2 M-jup for 0.'' 3 to 4.0 ''.
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| 8. |
- Samland, M., et al.
(författare)
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Spectral and atmospheric characterization of 51 Eridani b using VLT/SPHERE
- 2017
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 603
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Tidskriftsartikel (refereegranskat)abstract
- 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 (similar to 0.5 '', similar to 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 mu m). 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 f(sed). We find that the atmosphere is highly super-solar ([Fe/H] = 1.0 +/- 0.1 dex), and the low f(sed) = 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 M-gravity = 9.1(-3.3)(+4.9) M-J. The evolutionary model only provides a lower mass limit of > 2 M-J (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 M-J beyond separations of similar to 2.5 au and giant planets more massive than 2 M-J beyond 9 au.
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| 9. |
- Chauvin, G., et al.
(författare)
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Investigating the young solar system analog HD 95086 A combined HARPS and SPHERE exploration
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 617
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Tidskriftsartikel (refereegranskat)abstract
- Context. HD 95086 (A8V, 17 Myr) hosts a rare planetary system for which a multi-belt debris disk and a giant planet of 4-5 Mjup have been directly imaged.Aims. Our study aims to characterize the global architecture of this young system using the combination of radial velocity and direct imaging observations. We want to characterize the physical and orbital properties of HD 95086 b, search for additional planets at short and wide orbits and image the cold outer debris belt in scattered light.Methods. We used HARPS at the ESO 3.6 m telescope to monitor the radial velocity of HD 95086 over two years and investigate the existence of giant planets at less than 3 au orbital distance. With the IRDIS dual-band imager and the IFS integral field spectrograph of SPHERE at VLT, we imaged the faint circumstellar environment beyond 10 au at six epochs between 2015 and 2017.Results. We do not detect additional giant planets around HD 95086. We identify the nature (bound companion or background contaminant) of all point-like sources detected in the IRDIS field of view. None of them correspond to the ones recently discovered near the edge of the cold outer belt by ALMA. HD 95086 b is resolved for the first time in J-band with IFS. Its near-infrared spectral energy distribution is well fitted by a few dusty and/or young L7-L9 dwarf spectral templates. The extremely red 1-4 mu m spectral distribution is typical of low-gravity objects at the L/T spectral type transition. The planet's orbital motion is resolved between January 2015 and May 2017. Together with past NaCo measurements properly re-calibrated, our orbital fitting solutions favor a retrograde low to moderate-eccentricity orbit e = 0.2(-0.2)(+0.3), with a semi-major axis similar to 52 au corresponding to orbital periods of similar to 288 yr and an inclination that peaks at i = 141 degrees, which is compatible with a planet-disk coplanar configuration. Finally, we report the detection in polarimetric differential imaging of the cold outer debris belt between 100 and 300 au, consistent in radial extent with recent ALMA 1.3 mm resolved observations.
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| 10. |
- Keppler, M., et al.
(författare)
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Gap, shadows, spirals, and streamers : SPHERE observations of binary-disk interactions in GG Tauri A
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 639
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Tidskriftsartikel (refereegranskat)abstract
- Context. A large portion of stars is found to be part of binary or higher-order multiple systems. The ubiquity of planets found around single stars raises the question of whether and how planets in binary systems form. Protoplanetary disks are the birthplaces of planets, and characterizing them is crucial in order to understand the planet formation process.Aims. Our goal is to characterize the morphology of the GG Tau A disk, one of the largest and most massive circumbinary disks. We also aim to trace evidence for binary-disk interactions.Methods. We obtained observations in polarized scattered light of GG Tau A using the SPHERE/IRDIS instrument in the H-band filter. We analyzed the observed disk morphology and substructures. We ran 2D hydrodynamical models to simulate the evolution of the circumbinary ring over the lifetime of the disk.Results. The disk and also the cavity and the inner region are highly structured, with several shadowed regions, spiral structures, and streamer-like filaments. Some of these are detected here for the first time. The streamer-like filaments appear to connect the outer ring with the northern arc. Their azimuthal spacing suggests that they may be generated through periodic perturbations by the binary, which tear off material from the inner edge of the outer disk once during each orbit. By comparing observations to hydrodynamical simulations, we find that the main features, in particular, the gap size, but also the spiral and streamer filaments, can be qualitatively explained by the gravitational interactions of a binary with a semimajor axis of similar to 35 au on an orbit coplanar with the circumbinary ring.
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