* Astronomy

Title: The Gemini NICI Planet-Finding Campaign : Discovery of a Substellar L Dwarf Companion to the Nearby Young M Dwarf CD-35 2722
Authors: Zahed Wahhaj, Michael C. Liu, Beth A. Biller, Fraser Clarke, Eric L. Nielsen, Laird M. Close, Thomas L. Hayward, Eric E. Mamajek, Michael Cushing, Trent Dupuy, Matthias Tecza, Niranjan Thatte, Mark Chun, Christ Ftaclas, Markus Hartung, I. Neill Reid, Evgenya L. Shkolnik, Silvia H. P. Alencar, Pawel Artymowicz, Alan Boss, Elisabethe de Gouveia Dal Pino, Jane Gregorio-Hetem, Shigeru Ida, Marc Kuchner, Douglas N. C. Lin, Douglas W. Toomey

We present the discovery of a wide (67 AU) substellar companion to the nearby (21 pc) young solar-metallicity M1 dwarf CD-35 2722, a member of the ~100 Myr AB Doradus association. Two epochs of astrometry from the NICI Planet-Finding Campaign confirm that CD-35 2722 B is physically associated with the primary star. Near-IR spectra indicate a spectral type of L4\pm1 with a moderately low surface gravity, making it one of the coolest young companions found to date. The absorption lines and near-IR continuum shape of CD-35 2722 B agree especially well the dusty field L4.5 dwarf 2MASS J22244381-0158521, while the near-IR colours and absolute magnitudes match those of the 5 Myr old L4 planetary-mass companion, 1RXS J160929.1-210524 b. Overall, CD-35 2722 B appears to be an intermediate-age benchmark for L-dwarfs, with a less peaked H-band continuum than the youngest objects and near-IR absorption lines comparable to field objects. We fit Ames-Dusty model atmospheres to the near-IR spectra and find T=1700-1900 K and log(g) =4.5±0.5. The spectra also show that the radial velocities of components A and B agree to within ±10 km/s, further confirming their physical association. Using the age and bolometric luminosity of CD-35 2722 B, we derive a mass of 31±8 Mjup from the Lyon/Dusty evolutionary models. Altogether, young late-M to mid-L type companions appear to be over-luminous for their near-IR spectral type compared to field objects, in contrast to the under-luminosity of young late-L and early-T dwarfs.

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