Astrophys. J., 777, L20 (2013/November-2)
The extremely red, young l dwarf PSO J318.5338-22.8603: a free-floating planetary-mass analog to directly imaged young gas-giant planets.
LIU M.C., MAGNIER E.A., DEACON N.R., ALLERS K.N., DUPUY T.J., KOTSON M.C., ALLER K.M., BURGETT W.S., CHAMBERS K.C., DRAPER P.W., HODAPP K.W., JEDICKE R., KAISER N., KUDRITZKI R.-P., METCALFE N., MORGAN J.S., PRICE P.A., TONRY J.L. and WAINSCOAT R.J.
Abstract (from CDS):
We have discovered using Pan-STARRS1 an extremely red late-L dwarf, which has (J - K)MKO= 2.78 and (J - K)2MASS= 2.84, making it the reddest known field dwarf and second only to 2MASS J1207-39b among substellar companions. Near-IR spectroscopy shows a spectral type of L7±1 and reveals a triangular H-band continuum and weak alkali (K I and Na I) lines, hallmarks of low surface gravity. Near-IR astrometry from the Hawaii Infrared Parallax Program gives a distance of 24.6±1.4 pc and indicates a much fainter J-band absolute magnitude than field L dwarfs. The position and kinematics of PSO J318.5-22 point to membership in the β Pic moving group. Evolutionary models give a temperature of 1160+30–40 K and a mass of 6.5+1.3–1.0 MJup, making PSO J318.5-22 one of the lowest mass free-floating objects in the solar neighborhood. This object adds to the growing list of low-gravity field L dwarfs and is the first to be strongly deficient in methane relative to its estimated temperature. Comparing their spectra suggests that young L dwarfs with similar ages and temperatures can have different spectral signatures of youth. For the two objects with well constrained ages (PSO J318.5-22 and 2MASS J0355+11), we find their temperatures are ~400 K cooler than field objects of similar spectral type but their luminosities are similar, i.e., these young L dwarfs are very red and unusually cool but not "underluminous." Altogether, PSO J318.5-22 is the first free-floating object with the colors, magnitudes, spectrum, luminosity, and mass that overlap the young dusty planets around HR 8799 and 2MASS J1207-39.
brown dwarfs - parallaxes - planets and satellites: atmospheres - proper motions - solar neighborhood - surveys
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