tfaw survey – I. Wavelet-based denoising of K2 light curves. Discovery and validation of two new Earth-sized planets in K2 campaign 1

Abstract

The wavelet-based detrending and denoising method TFAW is applied for the first time to EVEREST 2.0-corrected light curves to further improve the photometric precision of almost all K2 observing campaigns (C1-C8, C12-C18). The performance of both methods is evaluated in terms of 6 hr combined differential photometric precision (CDPP), simulated transit detection efficiency, and planet characterization in different SNR regimes. On average, TFAW median 6hr CDPP is $\sim 30\%$ better than the one achieved by EVEREST 2.0 for all observing campaigns. Using the transit least-squares (TLS) algorithm, we show that the transit detection efficiency for simulated Earth-Sun-like systems is ∼8.5 × higher for TFAW-corrected light curves than for EVEREST 2.0 ones. Using the light curves of two confirmed exoplanets, K2-44 b (high-SNR) and K2-298 b (low-SNR), we show that TFAW yields better MCMC posterior distributions, transit parameters compatible with the cataloged ones but with smaller uncertainties and narrows the credibility intervals. We use the combination of TFAW’s improved photometric precision and TLS enhancement of the signal detection efficiency for weak signals to search for new transit candidates in K2 observing campaign 1. We report the discovery of two new K2-C1 Earth-sized planets statistically validated, using the vespa software: EPIC 201170410.02, with a radius of 1.047$^{+0.276}_{-0.257}R_{\oplus }$ planet orbiting an M-type star, and EPIC 201757695.02, with a radius of 0.908$^{+0.059}_{-0.064}R_{\oplus }$ planet orbiting a K-type star. EPIC 201757695.02 is the 9-th smallest planet ever discovered in K2-C1, and the 39-th smallest in all K2 campaigns.

TFAW survey II: six newly validated planets and 13 planet candidates fromK2

“…The survey makes use of TFAW, a novel wavelet-based detrending and denoising algorithm developed by del Ser et al (2018), the EVEREST 2.0 (Luger et al 2018) processed K2 light curves, and the TLS ) transit search algorithm. As shown in del Ser & Fors (2020), TFAW delivers both better photometric precision and planet characterization than any detrending method applied to K2 light curves. The increased photometric precision achieved with TFAW, especially for faint K2 magnitudes, together with TLS improved capabilities to detect small planets, enable us to detect new, Earth-sized, and smaller planets orbiting G-, K-and M-type stars.…”

“…The increased photometric precision achieved with TFAW, especially for faint K2 magnitudes, together with TLS improved capabilities to detect small planets, enable us to detect new, Earth-sized, and smaller planets orbiting G-, K-and M-type stars. As an example of this, del Ser & Fors (2020) reported the discovery of two new statistically validated Earth-sized planets, K2-327 b, and K2-328 b, orbiting an M-type and a K-type star, respectively.…”