Astron. J., 155, 238-238 (2018/June-0)
Spitzer light curves of the young, planetary-mass TW Hya members 2MASS J11193254-1137466AB and WISEA J114724.10-204021.3.
SCHNEIDER A.C., HARDEGREE-ULLMAN K.K., CUSHING M.C., KIRKPATRICK J.D. and SHKOLNIK E.L.
Abstract (from CDS):
We present Spitzer Space Telescope time-series photometry at 3.6 and 4.5 µm 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 µm and 1.108+0.093–0.094% at 4.5 µm 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 µm and 0.453 ± 0.037% at 4.5 µm, 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 µm 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 µm 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.
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