WISEP J004701.06+680352.1: An Intermediate Surface Gravity, Dusty Brown Dwarf in the AB Dor Moving Group
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We present spectroscopy, astrometry, and photometry of the brown dwarf WISEP J004701.06680352.1 W004768, an unusually red field L dwarf at a distance of 12.2 or - 0.4 pc. The three-dimensional space motion identifies it as a member of the AB Dor Moving Group, an identification supported by our classification of W004768 as intermediate surface gravity INT-G using the Allers Liu near-infrared classification system. This moving group membership implies near-solar metallicity, age 100-125 Myr, M approx. equal 0.018M solar mass, and log g approx. equal 4.5 the thick condensate clouds needed to explain the infrared spectrum are, therefore, a result of surface gravity that is lower than that of ordinary field brown dwarfs. From the observed luminosity and evolutionary model radius, we find Teff approx. equal 1300 K, a temperature normally associated with early T dwarfs. Thick clouds are also used to explain the spectral properties of directly imaged giant planets, and we discuss the successes and challenges for such substellar models in matching the observed optical and infrared spectra. W004768 shows that cloud thickness is more sensitive to intermediate surface gravity than in most models. We also present a trigonometric parallax of the dusty L6 dwarf 2MASS J214816284003593. It lies at 8.060 or - 0.036 parsecs its astrometry is consistent with the view that it is older and metal-rich.