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Register a new userInvestigation of the inner structures around HD169142 with VLT/SPHERE
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We present observations of the Herbig Ae star HD169142 with 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 $sim$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 $K_S$ 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 $sim$93 mas separation and position angle of 355$^{circ}$, 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 $sim$100 mas. Follow-up observations are necessary to confirm the detection and the nature of this source and structure.
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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 $beta$ 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 YJ bands and the H2H3 doublet. The disk is clearly detected up to 1.5 ($sim110$ au) from the star and appears as a ring, with an inclination $isim83$ degree, and a peak density position at $sim 70$ 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 $2 M_J$. 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.
We studied the well known circumstellar disk around the Herbig Ae/Be star HD 97048 with high angular resolution to reveal undetected structures in the disk, which may be indicative of disk evolutionary processes such as planet formation. We used the IRDIS near-IR subsystem of the extreme adaptive optics imager SPHERE at the ESO/VLT to study the scattered light from the circumstellar disk via high resolution polarimetry and angular differential imaging. We imaged the disk in unprecedented detail and revealed four ring-like brightness enhancements and corresponding gaps in the scattered light from the disk surface with radii between 39 au and 341 au. We derived the inclination and position angle as well as the height of the scattering surface of the disk from our observational data. We found that the surface height profile can be described by a single power law up to a separation ~270 au. Using the surface height profile we measured the scattering phase function of the disk and found that it is well consistent with theoretical models of compact dust aggregates. We discuss the origin of the detected features and find that low mass (< 1 M_Jup) nascent planets are a possible explanation.
Context. Direct imaging of debris discs gives important information about their nature, their global morphology, and allows us to identify specific structures possibly in connection with the presence of gravitational perturbers. It is the most straightforward technique to observe planetary systems as a whole. Aims. We present the first resolved images of the debris disc around the young F-type star HD 160305, detected in scattered light using the VLT/SPHERE instrument in the near infrared. Methods. We used a post-processing method based on angular differential imaging and synthetic images of debris discs produced with a disc modelling code (GRaTer) to constrain the main characteristics of the disc around HD 160305. All of the point sources in the field of the IRDIS camera were analysed with an astrometric tool to determine whether they are bound objects or background stars. Results. We detect a very inclined (~ 82{deg}) ring-like debris disc located at a stellocentric distance of about 86au (deprojected width ~27 au). The disc displays a brightness asymmetry between the two sides of the major axis, as can be expected from scattering properties of dust grains. We derive an anisotropic scattering factor g>0.5. A second right-left asymmetry is also observed with respect to the minor axis. We measure a surface brightness ratio of 0.73 $pm$ 0.18 between the bright and the faint sides. Because of the low signal-to-noise ratio (S/N) of the images we cannot easily discriminate between several possible explanations for this left-right asymmetry, such as perturbations by an unseen planet, the aftermath of the breakup of a massive planetesimal, or the pericenter glow effect due to an eccentric ring. Two epochs of observations allow us to reject the companionship hypothesis for the 15 point sources present in the field.
The quest to discover exoplanets is one of the most important missions in astrophysics, and is widely performed using the transit method, which allows for the detection of exoplanets down to the size of Mercury. However, to confirm these detections, additional vetting is mandatory. We selected six K2 targets from campaigns #1 to #8 that show transit light curves corresponding to Earth-sized to Neptune-sized exoplanets. We aim to discard some scenarios that could mimic an exoplanetary transit, leading to a misinterpretation of the data. We performed direct imaging observations using the SPHERE/VLT instrument to probe the close environment of these stars. For five of the K2 targets, we report no detection and we give the detection limits. For EPIC 206011496, we detect a 0.38 $pm$ 0.06 $M_{odot}$ companion at a separation of 977.12 $pm$ 0.73 mas (140.19 $pm$ 0.11 au). The spectral analysis corresponds to an M4-7 star, and the analysis of the proper motion shows that it is bounded to the primary star. EPIC 206011496 also hosts an Earth-like planetary candidate. If it transits the primary star, its radius is consistent with that of a super-Earth. However, if it transits the companion star, it falls into the mini-Neptune regime.
Dusty debris disks around pre- and main-sequence stars are potential signposts for the existence of planetesimals and exoplanets. Giant planet formation is therefore expected to play a key role in the evolution of the disk. This is indirectly confirmed by extant sub-millimeter near-infrared images of young protoplanetary and cool dusty debris disks around main sequence stars usually showing substantial spatial structures. A majority of recent discoveries of imaged giant planets have been obtained around young, early-type stars hosting a circumstellar disk. In this context, we have carried out a direct imaging program designed to maximize our chances of giant planet discovery and targeting twenty-two young, early-type stars. About half of them show indication of multi-belt architectures. Using the IRDIS dual-band imager and the IFS integral field spectrograph of SPHERE to acquire high-constrast coronagraphic differential near-infrared images, we have conducted a systematic search in the close environment of these young, dusty and early-type stars. We confirmed that companions detected around HIP 34276, HIP 101800 and HIP 117452 are stationary background sources and binary companions. The companion candidates around HIP 8832, HIP 16095 and HIP 95619 are determined as background contamination. For stars for which we infer the presence of debris belts, a theoretical minimum mass for planets required to clear the debris gaps can be calculated . The dynamical mass limit is at least $0.1 M_J$ and can exceed $1 M_J$. Direct imaging data is typically sensitive to planets down to $sim 3.6 M_J$ at 1 $$, and $1.7 M_J$ in the best case. These two limits tightly constrain the possible planetary systems present around each target. These systems will be probably detectable with the next generation of planet imagers.
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