A Relationship Between Stellar Age and Spot Coverage. (arXiv:2002.09135v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Morris_B/0/1/0/all/0/1">Brett M. Morris</a>

We investigate starspot distributions consistent with space-based photometry
of F, G, and K stars in six stellar associations ranging in age from 10 Myr to
4 Gyr. We show that a simple light curve statistic called the “smoothed
amplitude” is proportional to stellar age as $t^{-1/2}$, following a
Skumanich-like spin-down relation. We marginalize over the unknown stellar
inclinations by forward modeling the ensemble of light curves for direct
comparison with the Kepler, K2 and TESS photometry. We sample the posterior
distributions for spot coverage with Approximate Bayesian Computation. We find
typical spot coverages in the range 1-10% which decrease with increasing
stellar age. The spot coverage is proportional to $t^n$ where $n =-0.37 pm
0.16$, also statistically consistent with a Skumanich-like $t^{-1/2}$ decay of
starspot coverage with age. We apply two techniques to estimate the spot
coverage of young exoplanet-hosting stars likely to be targeted for
transmission spectroscopy with the James Webb Space Telescope, and estimate the
bias in exoplanet radius measurements due to varying starspot coverage.

We investigate starspot distributions consistent with space-based photometry
of F, G, and K stars in six stellar associations ranging in age from 10 Myr to
4 Gyr. We show that a simple light curve statistic called the “smoothed
amplitude” is proportional to stellar age as $t^{-1/2}$, following a
Skumanich-like spin-down relation. We marginalize over the unknown stellar
inclinations by forward modeling the ensemble of light curves for direct
comparison with the Kepler, K2 and TESS photometry. We sample the posterior
distributions for spot coverage with Approximate Bayesian Computation. We find
typical spot coverages in the range 1-10% which decrease with increasing
stellar age. The spot coverage is proportional to $t^n$ where $n =-0.37 pm
0.16$, also statistically consistent with a Skumanich-like $t^{-1/2}$ decay of
starspot coverage with age. We apply two techniques to estimate the spot
coverage of young exoplanet-hosting stars likely to be targeted for
transmission spectroscopy with the James Webb Space Telescope, and estimate the
bias in exoplanet radius measurements due to varying starspot coverage.

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