Possible Bright Starspots on TRAPPIST-1

<jats:title>Abstract</jats:title> <jats:p>The M8V star TRAPPIST-1 hosts seven roughly Earth-sized planets and is a promising target for exoplanet characterization. <jats:italic>Kepler</jats:italic>/<jats:italic>K2</jats:italic> 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 <jats:italic>Spitzer</jats:italic> light curve at 4.5 <jats:italic>μ</jats:italic>m. If the rotational modulation is due to starspots, persistent dark spots can be excluded from the lack of photometric variability in the <jats:italic>Spitzer</jats:italic> light curve. We construct a photometric model for rotational modulation due to photospheric bright spots on TRAPPIST-1 that is consistent with both the <jats:italic>Kepler</jats:italic> and <jats:italic>Spitzer</jats:italic> light curves. The maximum-likelihood model with three spots has typical spot sizes of <jats:italic>R</jats:italic> <jats:sub>spot</jats:sub>/<jats:italic>R</jats:italic> <jats:sub>⋆</jats:sub> ≈ 0.004 at temperature <jats:italic>T</jats:italic> <jats:sub>spot</jats:sub> ≳ 5300 ± 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-day periodicity may not be a rotational signal, but rather a characteristic timescale of active regions.</jats:p>