Exoplanet Atmospheric Refraction Effects in the Kepler Sample

TL;DR

This study investigates the detectability of atmospheric refraction effects in Kepler exoplanets, aiming to understand atmospheric composition and properties, especially in relation to the period-radius valley and atmospheric evaporation.

Contribution

It introduces a method to detect atmospheric refraction effects in Kepler data and applies it to analyze atmospheric properties across different exoplanet populations.

Findings

Strong refraction signals detected above the period-radius valley.

Refraction effects consistent with thick, hazy atmospheres are rare.

Evidence suggests clouds and hazes dampen refraction signals in observed exoplanets.

Abstract

We present an analysis on the detection viability of refraction effects in Kepler's exoplanet atmospheres using binning techniques for their light curves in order to compare against simulated refraction effects. We split the Kepler exoplanets into sub-populations according to orbital period and planetary radius, then search for out-of-transit changes in the relative flux associated with atmospheric refraction of starlight. The presence of refraction effects - or lack thereof - may be used to measure and set limits on the bulk properties of an atmosphere, including mean molecular weight or the presence of hazes. In this work, we use the presence of refraction effects to test whether exoplanets above the period-radius valley have H/He atmospheres, which high levels of stellar radiation could evaporate away, in turn leaving rocky cores below the valley. We find strong observational evidence of refraction effects for exoplanets above the period-radius valley based on Kepler photometry, however those related to optically thin H/He atmospheres are not common in the observed planetary population. This result may be attributed to signal dampening caused by clouds and hazes, consistent with the optically thick and intrinsically hotter atmospheres of Kepler exoplanets caused by relatively close host star proximity.