Planets Around Low-Mass Stars (PALMS). VI. Discovery of a Remarkably Red Planetary-Mass Companion to the AB Dor Moving Group Candidate 2MASS J22362452+4751425

• Published in: arXiv.org 2016-11
• Main Authors: Bowler, Brendan, Liu, Michael, Mawet, Dimitri, Ngo, Henry, Malo, Lison, Mace, Gregory, McLane, Jacob, Lu, Jessica, Tristan, Isaiah, Hinkley, Sasha, Hillenbrand, Lynne, Shkolnik, Evgenya, Benneke, Bjorn, Best, William
• Format: Article
• Language: English
• Subjects: Absorption; Adaptive optics; Brown dwarf stars; Color; Color-magnitude diagram; Extrasolar planets; Jupiter; Kinematics; Low mass stars; Photosphere; Planet detection; Planetary atmospheres
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1611.00364

We report the discovery of an extremely red planetary-mass companion to 2MASS J22362452+4751425, a \(\approx\)0.6 \(M_{\odot}\) late-K dwarf likely belonging to the \(\sim\)120 Myr AB Doradus moving group. 2M2236+4751 b was identified in multi-epoch NIRC2 adaptive optics imaging at Keck Observatory at a separation of 3.7\("\), or 230 \(\pm\) 20 AU in projection at the kinematic distance of 63 \(\pm\) 5 pc to its host star. Assuming membership in the AB Dor group, as suggested from its kinematics, the inferred mass of 2M2236+4751 b is 11-14 \(M_\mathrm{Jup}\). Follow-up Keck/OSIRIS \(K\)-band spectroscopy of the companion reveals strong CO absorption similar to other faint red L dwarfs and lacks signs of methane absorption despite having an effective temperature of \(\approx\)900-1200 K. With a (\(J\)-\(K\))\(_\mathrm{MKO}\) color of 2.69 \(\pm\) 0.12 mag, the near-infrared slope of 2M2236+4751 b is redder than all of the HR 8799 planets and instead resembles the \(\approx\)23 Myr isolated planetary-mass object PSO J318.5-22, implying that similarly thick photospheric clouds can persist in the atmospheres of giant planets at ages beyond 100 Myr. In near-infrared color-magnitude diagrams, 2M2236+4751 b is located at the tip of the red L dwarf sequence and appears to define the "elbow" of the AB Dor substellar isochrone separating low-gravity L dwarfs from the cooler young T dwarf track. 2M2236+4751 b is the reddest substellar companion to a star and will be a valuable benchmark to study the shared atmospheric properties of young low-mass brown dwarfs and extrasolar giant planets.