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arXiv · 1804.06917

Spitzer Light Curves of the Young, Planetary-Mass TW Hya Members 2MASS J11193254-1137466AB and WISEA J114724.10-204021.3

Adam C. Schneider·Kevin K. Hardegree-Ullman·Michael C. Cushing·J. Davy Kirkpatrick·Evgenya L. Shkolnik
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Abstract

We present Spitzer Space Telescope time-series photometry at 3.6 and 4.5 $μ$m of 2MASS J11193254$-$1137466AB and WISEA J114724.10$-$204021.3, two planetary-mass, late-type ($\sim$L7) brown dwarf members of the $\sim$10 Myr old TW Hya Association. These observations were taken in order to investigate whether or not a tentative trend of increasing variability amplitude with decreasing surface gravity seen for L3-L5.5 dwarfs extends to later-L spectral types and to explore the angular momentum evolution of low-mass objects. We examine each light curve for variability and find a rotation period of 19.39$^{+0.33}_{-0.28}$ hours and semi-amplitudes of 0.798$^{+0.081}_{-0.083}$% at 3.6 $μ$m and 1.108$^{+0.093}_{-0.094}$% at 4.5 $μ$m for WISEA J114724.10$-$204021.3. For 2MASS J11193254$-$1137466AB, we find a single period of 3.02$^{+0.04}_{-0.03}$ hours with semi-amplitudes of 0.230$^{+0.036}_{-0.035}$% at 3.6 $μ$m and 0.453 $\pm$ 0.037% at 4.5 $μ$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 $μ$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 $μ$m for young, late-type Ls. We also find a median rotation period of young brown dwarfs (10-300 Myr) of $\sim$10 hr, more than twice the value of the median rotation period of field age brown dwarfs ($\sim$4 hr), a clear signature of brown dwarf rotational evolution.

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Adam C. Schneider, Kevin K. Hardegree-Ullman, Michael C. Cushing, J. Davy Kirkpatrick, Evgenya L. Shkolnik. 2018-04-18. Spitzer Light Curves of the Young, Planetary-Mass TW Hya Members 2MASS J11193254-1137466AB and WISEA J114724.10-204021.3. https://doi.org/10.3847/1538-3881%2Faabfc2

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