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

June 2018 • 2018AJ....155..238S

Authors • Schneider, Adam C. • Hardegree-Ullman, Kevin K. • Cushing, Michael C. • Kirkpatrick, J. Davy • Shkolnik, Evgenya L.

Abstract • 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.

Links

• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2018AJ....155..238S
• PDF https://iopscience.iop.org/article/10.3847/1538-3881/aabfc2/pdf
• PDF https://stacks.iop.org/1538-3881/155/238/pdf
• PREPRINT http://arxiv.org/abs/1804.06917
• DATA https://irsa.ipac.caltech.edu/bibdata/2018/S/2018AJ....155..238S.html
• ELECTR https://doi.org/10.3847%2F1538-3881%2Faabfc2