The Starspots of HAT-P-11: Evidence for a Solar-like Dynamo

Abstract

We measure the starspot radii and latitude distribution on the K4 dwarf HAT-P-11 from Kepler short-cadence photometry. We take advantage of starspot occultations by its highly-misaligned planet to compare the spot size and latitude distributions to those of sunspots. We find that the spots of HAT-P-11 are distributed in latitude much like sunspots near solar activity maximum, with mean spot latitude of $16\pm 1$ degrees. The majority of starspots of HAT-P-11 have physical sizes that closely resemble the sizes of sunspots at solar maximum. We estimate the mean spotted area coverage on HAT-P-11 is $3_{-1}^{+6}\%$, roughly two orders of magnitude greater than the typical solar spotted area.

28 pages, 16 figures, accepted for publication in the Astrophysical Journal (August 7, 2017)

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• Chromospheric Activity of HAT-P-11: an Unusually Active Planet-Hosting K Star
• Activity time series of old stars from late F to early K. I. Simulating radial velocity, astrometry, photometry, and chromospheric emission
• Developing a vision for exoplanetary transit spectroscopy: a shared window on the analysis of planetary atmospheres and of stellar magnetic structure