Discovery of Six Optical Phase Curves with K2

TL;DR

This study systematically searches for optical phase curves in K2 data, identifying six new cases, and demonstrates the potential for phase curve analysis to validate exoplanets and measure planetary properties.

Contribution

The paper reports the discovery of six new optical phase curves in K2 data, including hot Jupiters and super-Earths, using novel filtering techniques and validation methods.

Findings

Six new phase curves identified in K2 data.

Photometric masses consistent with RV measurements.

Detection of secondary eclipse in HATS-11b.

Abstract

We have systematically searched for the phase curves among the planets discovered by \textit{K2}. Using the reported planetary parameters, we screen out the best potential candidates, and examine their light curves in detail. For our work, we consider light curves from two different detrending pipelines - \texttt{EVEREST} and \texttt{K2SFF}. In order to remove stellar variability and systematics, we test three different filtering techniques: spline, phasma (median-filtering) and Butterworth (harmonics filtering), and use Butterworth filtered light curves for the subsequent analysis. We have identified 6 previously unreported phase curves among the planets observed with \textit{K2}: K2-31b, HATS-9b, HATS-11b, K2-107b, K2-131b, and K2-106b. The first four of these are hot Jupiters for which we find the photometric masses consistent with their RV-based masses within 2$\sigma$, 1$\sigma$, 1$\sigma$, and 3$\sigma$ respectively with comparatively low geometric albedos, while the last two are ultra-short period super-Earths with phase curves dominated by reflective and thermal components. We also detect a secondary eclipse in HATS-11b at 62$\pm$12 ppm. We thus deem it to be possible to validate the planetary nature of selected \textit{K2}, and suggest similar vetting could be used for the ongoing \textit{TESS} mission.