Discovery of Six Optical Phase Curves with K2

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). We find the Butterworth as the most robust performer in our injection-retrieval test. We have identified 6 previously unreported phase curve 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 that have estimated photometric masses consistent with their RV-based masses within 2$\sigma$, 1$\sigma$, 1$\sigma$, and 3$\sigma$ respectively, 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. We thus deem it to be possible to validate the planetary nature of selected \textit{K2} targets using photometry alone without RV, and suggest similar vetting could be used for the ongoing \textit{TESS} mission.

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