DISCOVERY OF A WIDE PLANETARY-MASS COMPANION TO THE YOUNG M3 STAR GU PSC

Abstract

We present the discovery of a co-moving planetary-mass companion ~42" (~2000\nAU) from a young M3 star, GU Psc, likely member of the young AB Doradus Moving\nGroup (ABDMG). The companion was first identified via its distinctively red i -\nz color (> 3.5) through a survey made with Gemini-S/GMOS. Follow-up\nCanada-France-Hawaii Telescope/WIRCam near-infrared (NIR) imaging,\nGemini-N/GNIRS NIR spectroscopy and Wide-field Infrared Survey Explorer\nphotometry indicate a spectral type of T3.5+-1 and reveal signs of low gravity\nwhich we attribute to youth. Keck/Adaptive Optics NIR observations did not\nresolve the companion as a binary. A comparison with atmosphere models\nindicates Teff = 1000-1100 K and logg = 4.5-5.0. Based on evolution models,\nthis temperature corresponds to a mass of 9-13 MJup for the age of ABDMG\n(70-130 Myr). The relatively well-constrained age of this companion and its\nvery large angular separation to its host star will allow its thorough\ncharacterization and will make it a valuable comparison for planetary-mass\ncompanions that will be uncovered by forthcoming planet-finder instruments such\nas Gemini Planet Imager and SPHERE.\n