Possible Bright Starspots on TRAPPIST-1

Brett M. Morris, Eric Agol, James R. A. Davenport, Suzanne L. Hawley
(Submitted on 12 Mar 2018)

The M8V star TRAPPIST-1 hosts seven roughly Earth-sized planets and is a promising target for exoplanet characterization. Kepler/K2 Campaign 12 observations of TRAPPIST-1 in the optical show an apparent rotational modulation with a 3.3 day period, though that rotational signal is not readily detected in the Spitzer light curve at 4.5 $\mu$m. If the rotational modulation is due to starspots, persistent dark spots can be excluded from the lack of photometric variability in the Spitzer light curve. We construct a photometric model for rotational modulation due to photospheric bright spots on TRAPPIST-1 which is consistent with both the Kepler and Spitzer light curves. The maximum-likelihood model with three spots has typical spot sizes of $R_\mathrm{spot}/R_\star \approx 0.004$ at temperature $T_\mathrm{spot} \gtrsim 5300 \pm 200$ K. We also find that large flares are observed more often when the brightest spot is facing the observer, suggesting a correlation between the position of the bright spots and flare events. In addition, these flares may occur preferentially when the spots are increasing in brightness, which suggests that the 3.3 d periodicity may not be a rotational signal, but rather a characteristic timescale of active regions.

Comments:    Accepted by ApJ March 12, 2018
Subjects:    Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)
Cite as:    arXiv:1803.04543 [astro-ph.SR] (or arXiv:1803.04543v1 [astro-ph.SR] for this version)
Submission history
From: Brett Morris
[v1] Mon, 12 Mar 2018 21:33:52 GMT (2278kb,D)
https://arxiv.org/abs/1803.04543