Discovery of a warm, dusty giant planet around HIP 65426
Authors: Chauvin G. , Desidera S. , Lagrange A.-M. , Vigan A. , Gratton R. , Langlois M. , Bonnefoy M. , Beuzit J.-L. , Feldt M. , Mouillet D. , Meyer M. , Cheetham A. , Biller B. , Boccaletti A. , D’Orazi V. , Galicher R. , Hagelberg J. , Maire A.-L. , Mesa D. , Olofsson J. , Samland M. , Schmidt T. O. B. , Sissa E. , Bonavita M. , Charnay B. , Cudel M. , Daemgen S. , Delorme P. , Janin-Potiron P. , Janson M. , Keppler M. , Le Coroller H. , Ligi R. , Marleau G. D. , Messina S. , Mollière P. , Mordasini C. , Müller A. , Peretti S. , Perrot C. , Rodet L. , Rouan D. , Zurlo A. , Dominik C. , Henning T. , Menard F. , Schmid H.-M. , Turatto M. , Udry S. , Vakili F. , Abe L. , Antichi J. , Baruffolo A. , Baudoz P. , Baudrand J. , Blanchard P. , Bazzon A. , Buey T. , Carbillet M. , Carle M. , Charton J. , Cascone E. , Claudi R. , Costille A. , Deboulbe A. , De Caprio V. , Dohlen K. , Fantinel D. , Feautrier P. , Fusco T. , Gigan P. , Giro E. , Gisler D. , Gluck L. , Hubin N. , Hugot E. , Jaquet M. , Kasper M. , Madec F. , Magnard Y. , Martinez P. , Maurel D. , Le Mignant D. , Möller-Nilsson O. , Llored M. , Moulin T. , Origné A. , Pavlov A. , Perret D. , Petit C. , Pragt J. , Puget P. , Rabou P. , Ramos J. , Rigal R. , Rochat S. , Roelfsema R. , Rousset G. , Roux A. , Salasnich B. , Sauvage J.-F. , Sevin A. , Soenke C. , Stadler E. , Suarez M. , Weber L. , Wildi F. , Antoniucci S. , Augereau J.-C. , Baudino J.-L. , Brandner W. , Engler N. , Girard J. , Gry C. , Kral Q. , Kopytova T. , Lagadec E. , Milli J. , Moutou C. , Schlieder J. , Szulágyi J. , Thalmann C. , Wahhaj Z. 
Published: August 2017

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 ~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 μm 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 MJup, Teff = 1300–1600 K and R = 1.5 ± 0.1 RJup 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 RJup).

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.