Lack of Inflated Radii for Kepler Giant Planet Candidates Receiving Modest Stellar Irradiation

TL;DR

This study refines the analysis of Kepler giant planet candidates and finds that planets receiving modest stellar irradiation do not exhibit inflated radii, challenging the universality of inflation mechanisms for hot Jupiters.

Contribution

It provides a refined photometric analysis of Kepler candidates and demonstrates that radius inflation is absent below a certain stellar irradiation threshold.

Findings

Inflated radii correlate with high stellar irradiation.

Giant planets with modest irradiation have radii independent of stellar flux.

Approximately 14% of candidates are likely false positives.

Abstract

The most irradiated transiting hot Jupiters are characterized by anomalously inflated radii, sometimes exceeding Jupiter's size by more than 60%. While different theoretical explanations have been applied, none of them provide a universal resolution to this observation, despite significant progress in the past years. We refine the photometric transit light curve analysis of 115 Kepler giant planet candidates based on public Q0-Q2 photometry. We find that 14% of them are likely false positives, based on their secondary eclipse depth. We report on planet radii vs. stellar flux. We find an increase in planet radii with increased stellar irradiation for the Kepler giant planet candidates, in good agreement with existing hot Jupiter systems. We find that in the case of modest irradiation received from the stellar host, giant planets do not have inflated radii, and appear to have radii independent of the host star incident flux. This finding suggests that the physical mechanisms inflating hot Jupiters become ineffective below a given orbit-averaged stellar irradiation level of ~2 10^8 erg s^-1 cm^-2.