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  • Spitzer Light Curves of the...
    Schneider, Adam C.; Hardegree-Ullman, Kevin K.; Cushing, Michael C.; Kirkpatrick, J. Davy; Shkolnik, Evgenya L.

    The Astronomical journal, 06/2018, Volume: 155, Issue: 6
    Journal Article

    We present Spitzer Space Telescope time-series photometry at 3.6 and 4.5 m of 2MASS J11193254−1137466AB and WISEA J114724.10−204021.3, two planetary-mass, late-type (∼L7) brown dwarf members of the ∼10 Myr old TW Hya Association. These observations were taken in order to investigate whether or not a tentative trend of increasing variability amplitude with decreasing surface gravity seen for L3-L5.5 dwarfs extends to later-L spectral types and to explore the angular momentum evolution of low-mass objects. We examine each light curve for variability and find a rotation period of 19.39+0.33−0.28 hr and semi-amplitudes of 0.798+0.081−0.083% at 3.6 m and 1.108+0.093−0.094% at 4.5 m for WISEA J114724.10−204021.3. For 2MASS J11193254−1137466AB, we find a single period of 3.02+0.04−0.03 hr with semi-amplitudes of 0.230+0.036−0.035% at 3.6 m and 0.453 0.037% at 4.5 m, which we find is possibly due to the rotation of one component of the binary. Combining our results with 12 other late-type L dwarfs observed with Spitzer from the literature, we find no significant differences between the 3.6 m amplitudes of low surface gravity and field gravity late-type L brown dwarfs at Spitzer wavelengths, and find tentative evidence (75% confidence) of higher amplitude variability at 4.5 m for young, late-type Ls. We also find a median rotation period of young brown dwarfs (10-300 Myr) of ∼10 hr, more than twice the value of the median rotation period of field-age brown dwarfs (∼4 hr), a clear signature of brown dwarf rotational evolution.