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Published January 2017 | Submitted + Published
Journal Article Open

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


We report the discovery of an extremely red planetary-mass companion to 2MASS J22362452+4751425, a ≈0.6 M⊙ late-K dwarf likely belonging to the ~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 ± 20 AU in projection at the kinematic distance of 63 ± 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_(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 ≈900–1200 K. With a (J–K)_(MKO) color of 2.69 ± 0.12 mag, the near-infrared slope of 2M2236+4751 b is redder than all of the HR 8799 planets and instead resembles the ≈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.

Additional Information

© 2016 The American Astronomical Society. Received 2016 August 28; revised 2016 October 12; accepted 2016 October 31; published 2016 December 21. Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. We thank A. Kraus for helpful discussions about the age of the host star and the entire Keck Observatory staff for their exceptional support. I.T. was supported by the Department of Astronomy at the University of Texas at Austin through the Cox Endowment and Board of Visitors Funds, as well as a NASA WIYN PI Data Award administered by the NASA Exoplanet Science Institute as part of NN-EXPLORE through the scientific partnership of NASA, the National Science Foundation, and the National Optical Astronomy Observatory. This paper includes data taken at The McDonald Observatory of The University of Texas at Austin. It is also based on observations obtained with ESPaDOnS, located at the Canada–France–Hawaii Telescope (CFHT). CFHT is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientique of France, and the University of Hawai'i. ESPaDOnS is a collaborative project funded by France (CNRS, MENESR, OMP, LATT), Canada (NSERC), CFHT and ESA. We utilized data products from 2MASS, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by NASA and the National Science Foundation. NASA's Astrophysics Data System Bibliographic Services together with the VizieR catalogue access tool and SIMBAD database operated at CDS, Strasbourg, France, were invaluable resources for this work. This work used the Immersion Grating Infrared Spectrometer (IGRINS) that was developed under a collaboration between the University of Texas at Austin and the Korea Astronomy and Space Science Institute (KASI) with the financial support of the US National Science Foundation under grant AST-1229522, to the University of Texas at Austin, and of the Korean GMT Project of KASI. This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by NASA. Finally, mahalo nui loa to the kama'āina of Hawai'i for their support of Keck and the Maunakea observatories. We are grateful to have been able to conduct observations from this mountain. Facilities: Keck:II (NIRC2) - , Keck:I (OSIRIS) - , Smith (IGRINS) - , IRTF (SpeX) - , CFHT (ESPaDOnS).

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Published - Bowler_2017_AJ_153_18.pdf

Submitted - 1611.00364.pdf


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