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.; Wainscoat, R.J.

Abstract

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$^{+1.3}_{-1.0}$ M Jup, 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.

Citation

Liu, M., Magnier, E., Deacon, N., Allers, K., Dupuy, T., Kotson, M., …Wainscoat, R. (2013). The Extremely Red, Young L Dwarf PSO J318.5338-22.8603: A Free-Floating Planetary-Mass Analog to Directly Imaged Young Gas-Giant Planets. Astrophysical Journal Letters, 777(2), Article L20. https://doi.org/10.1088/2041-8205/777/2/l20

• Journal Article Type: Article
• Publication Date: Nov 10, 2013
• Deposit Date: Apr 3, 2014
• Publicly Available Date: Jul 3, 2014
• Journal: Astrophysical Journal Letters
• Print ISSN: 2041-8205
• Electronic ISSN: 2041-8213
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 777
• Issue: 2
• Article Number: L20
• DOI: https://doi.org/10.1088/2041-8205/777/2/l20
• Keywords: Brown dwarfs, Parallaxes, Planets and satellites: atmospheres, Proper motions, Solar neighborhood, Surveys.