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- Chauvin, G., et al.
(författare)
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Discovery of a warm, dusty giant planet around HIP 65426
- 2017
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 605
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Tidskriftsartikel (refereegranskat)abstract
- Aims. The SHINE program is a high-contrast near-infrared survey of 600 young, nearby stars aimed at searching for and characterizing new planetary systems using VLT/SPHERE's unprecedented high-contrast and high-angular-resolution imaging capabilities. It is also intended to place statistical constraints on the rate, mass and orbital distributions of the giant planet population at large orbits as a function of the stellar host mass and age to test planet-formation theories.Methods. We used the IRDIS dual-band imager and the IFS integral field spectrograph of SPHERE to acquire high-contrast coronagraphic differential near-infrared images and spectra of the young A2 star HIP 65426. It is a member of the similar to 17 Myr old Lower Centaurus-Crux association. Results. At a separation of 830 mas (92 au projected) from the star, we detect a faint red companion. Multi-epoch observations confirm that it shares common proper motion with HIP 65426. Spectro-photometric measurements extracted with IFS and IRDIS between 0.95 and 2.2 mu m indicate a warm, dusty atmosphere characteristic of young low-surface-gravity L5-L7 dwarfs. Hot-start evolutionary models predict a luminosity consistent with a 6-12 M-Jup, T-eff = 1300-1600K and R = 1.5 +/- 0.1 R-Jup giant planet. Finally, the comparison with Exo-REM and PHOENIX BT-Settl synthetic atmosphere models gives consistent effective temperatures but with slightly higher surface gravity solutions of log(g) = 4.0-5.0 with smaller radii (1.0-1.3 R-Jup).Conclusions. Given its physical and spectral properties, HIP 65426 b occupies a rather unique placement in terms of age, mass, and spectral-type among the currently known imaged planets. It represents a particularly interesting case to study the presence of clouds as a function of particle size, composition, and location in the atmosphere, to search for signatures of non-equilibrium chemistry, and finally to test the theory of planet formation and evolution.
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| 2. |
- 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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