Variability of Kepler Solar-Like Stars Harboring Small Exoplanets

TL;DR

This study analyzes the variability of Kepler solar-like stars hosting small exoplanets on habitable zone timescales, highlighting the rarity of detecting very small planets around the quietest stars and discussing implications for habitability and detection.

Contribution

It provides a uniform analysis of Kepler solar-like stars with small exoplanets, emphasizing the relationship between stellar variability, brightness, and planet detection prospects.

Findings

Small exoplanets are detected mainly around photometrically quiet, bright stars.

Brighter, evolved stars like subgiants are promising targets for small planet searches.

Kepler's visible light observations are insensitive to chromospheric activity variability.

Abstract

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 $\le$2.5\re. The variability timescale examined is typical for habitable zone planets orbiting solar-like stars and we note that the discovery of the smallest exoplanets ($\le$1.2\re) with corresponding transit depths of less than $\sim$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.