A. Cheetham

Atmospheric characterization of Proxima b by coupling the SPHERE high-contrast imager to the ESPRESSO spectrograph

Context. The temperate Earth-mass planet Proxima b is the closest exoplanet to Earth and represents what may be our best ever opportunity to search for life outside the Solar System. Aims. We aim at directly detecting Proxima b and characterizing its atmosphere by spatially resolving the planet and obtaining high-resolution reflected-light spectra. Methods. We propose to develop a coupling interface between the SPHERE high-contrast imager and the new ESPRESSO spectrograph, both installed at ESO VLT. The angular separation of 37 mas between Proxima b and its host star requires the use of visible wavelengths to spatially resolve the planet on a 8.2-m telescope. At an estimated planet-to-star contrast of ~10^-7 in reflected light, Proxima b is extremely challenging to detect with SPHERE alone. However, the combination of a ~10^3-10^4 contrast enhancement from SPHERE to the high spectral resolution of ESPRESSO can reveal the planetary spectral features and disentangle them from the stellar ones. Results. We find that significant but realistic upgrades to SPHERE and ESPRESSO would enable a 5-sigma detection of the planet and yield a measurement of its true mass and albedo in 20-40 nights of telescope time, assuming an Earth-like atmospheric composition. Moreover, it will be possible to probe the O2 bands at 627, 686 and 760 nm, the water vapour band at 717 nm, and the methane band at 715 nm. In particular, a 3.6-sigma detection of O2 could be made in about 60 nights of telescope time. Those would need to be spread over 3 years considering optimal observability conditions for the planet. Conclusions. The very existence of Proxima b and the SPHERE-ESPRESSO synergy represent a unique opportunity to detect biosignatures on an exoplanet in the near future. It is also a crucial pathfinder experiment for the development of Extremely Large Telescopes and their instruments (abridged).

A narrow, edge-on disk resolved around HD 106906 with SPHERE

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 planets 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.

An M-dwarf star in the transition disk of Herbig HD142527; Physical parameters and orbital elements

S.L. acknowledges fruitful discussions with S. Casassus about the existence of HD 142527B and the inner disk of HD 142527A. This research made use of Astropy, a community-developed core Python package for Astronomy (Astropy Collaboration et al. 2013). This work was supported by the French National Agency for Research (ANR-13-JS05-0005) and the European Research Council (ERC-STG-639248). A.G. and A.S. acknowledge support from NSF Graduate Research Fellowship grant No. DGE-1232825 and NASA grant NNX11AF74G. J.O. acknowledges support from the Millennium Nucleus RC130007 (Chilean Ministry of Economy). I.B. acknowledges the European Research Council through grant ERC-AdG No. 320478-TOFU. Based on observations collected at the European Southern Observatory (ESO) during runs 088.C-0691(A), 090.C-0649(A), 091.C-0572(A), and 094.C-0608(A). Also based on observations obtained at the Gemini Observatory (programs GS-2014A-SV-406 and GS-ENG-GPI-COM), which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministerio da Ciencia, Tecnologia e Inovacao (Brazil) and Ministerio de Ciencia, Tecnologia e Innovacion Productiva (Argentina).

Spectral and atmospheric characterization of 51 Eridani b using VLT/SPHERE

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 μ 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 \hbox{

Investigating the young solar system analog HD 95086. A combined HARPS and SPHERE exploration

{f_{\rm sed} = 1.26^{+0.36}_{-0.29}}

Dynamical models to explain observations with SPHERE in planetary systems with double debris belts

} 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{

Observations of fast-moving features in the debris disk of AU Mic on a three-year timescale: Confirmation and new discoveries

{M_\mathrm{gravity} = 9.1^{+4.9}_{-3.3} \, {M}_\mathrm{J}}

First scattered light detection of a nearly edge-on transition disk around the T Tauri star RY Lupi

}. 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 ~2.5 au and giant planets more massive than 2 M J beyond 9 au.

Orbital and atmospheric characterization of the planet within the gap of the PDS 70 transition disk

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 gl ...

The GJ 504 system revisited: Combining interferometric, radial velocity, and high contrast imaging data★

Context. A large number of systems harboring a debris disk show evidence for a double belt architecture. One hypothesis for explaining the gap between the debris belts in these disks is the presence of one or more planets dynamically carving it. For this reason these disks represent prime targets for searching planets using direct imaging instruments, like the Spectro-Polarimetric High-constrast Exoplanet Research (SPHERE) at the Very Large Telescope. Aim. The goal of this work is to investigate this scenario in systems harboring debris disks divided into two components, placed, respectively, in the inner and outer parts of the system. All the targets in the sample were observed with the SPHERE instrument, which performs high-contrast direct imaging, during the SHINE guaranteed time observations. Positions of the inner and outer belts were estimated by spectral energy distribution fitting of the infrared excesses or, when available, from resolved images of the disk. Very few planets have been observed so far in debris disks gaps and we intended to test if such non-detections depend on the observational limits of the present instruments. This aim is achieved by deriving theoretical predictions of masses, eccentricities, and semi-major axes of planets able to open the observed gaps and comparing such parameters with detection limits obtained with SPHERE. Methods. The relation between the gap and the planet is due to the chaotic zone neighboring the orbit of the planet. The radial extent of this zone depends on the mass ratio between the planet and the star, on the semi-major axis, and on the eccentricity of the planet, and it can be estimated analytically. We first tested the different analytical predictions using a numerical tool for the detection of chaotic behavior and then selected the best formula for estimating a planet’s physical and dynamical properties required to open the observed gap. We then apply the formalism to the case of one single planet on a circular or eccentric orbit. We then consider multi-planetary systems: two and three equal-mass planets on circular orbits and two equal-mass planets on eccentric orbits in a packed configuration. As a final step, we compare each couple of values ( M p , a p ), derived from the dynamical analysis of single and multiple planetary models, with the detection limits obtained with SPHERE. Results. For one single planet on a circular orbit we obtain conclusive results that allow us to exclude such a hypothesis since in most cases this configuration requires massive planets which should have been detected by our observations. Unsatisfactory is also the case of one single planet on an eccentric orbit for which we obtained high masses and/or eccentricities which are still at odds with observations. Introducing multi planetary architectures is encouraging because for the case of three packed equal-mass planets on circular orbits we obtain quite low masses for the perturbing planets which would remain undetected by our SPHERE observations. The case of two equal-mass planets on eccentric orbits is also of interest since it suggests the possible presence of planets with masses lower than the detection limits and with moderate eccentricity. Our results show that the apparent lack of planets in gaps between double belts could be explained by the presence of a system of two or more planets possibly of low mass and on eccentric orbits whose sizes are below the present detection limits.