Tuesday, February 16, 2016

How Variable are the Host Stars of 'Small' (2.5 Earth Radius or Less) Exoplanets?

Variability of Kepler Solar-Like Stars Harboring Small Exoplanets


Howell et al


We examine Kepler light curve variability on habitable zone transit timescales for a large uniform sample of spectroscopically studied Kepler exoplanet host stars. The stars, taken from Everett et al. (2013) are solar-like in their properties and each harbors at least one exoplanet (or candidate) of radius ≤2.5\re. The variability timescale examined is typical for habitable zone planets orbiting solar-like stars and we note that the discovery of the smallest exoplanets (≤1.2\re) with corresponding transit depths of less than ∼0.18 mmag, occur for the brightest, photometrically quietest stars. Thus, these detections are quite rare in Kepler observations. Some brighter and more evolved stars (subgiants), the latter which often show large radial velocity jitter, are found to be among the photometrically quietest solar-like stars in our sample and the most likely small planet transit hunting grounds. The Sun is discussed as a solar-like star proxy to provide insights into the nature and cause of photometric variability. It is shown that Kepler′s broad, visible light observations are insensitive to variability caused by chromospheric activity that may be present in the observed stars.

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