Reanalyzing 55 Cnc with Bronez multitapers

Abstract

Modern exoplanet searching heavily relies on the generalized Lomb-Scargle periodogram (GLS) to ascertain the frequency domain representation of unevenly sampled radial velocity measurements. The GLS suffers from strong statistical biases, making it difficult to correctly extract planetary signals. We introduce to the astronomical community a novel frequency-domain analysis technique by adapting the Bronez (1988) multitaper method for radial velocity (RV) planet searches around 55 Cancri (55 Cnc). Using archival 55 Cnc RV measurements, we present multitaper power spectrum estimates (MPSE) and compare these with their Lomb-Scargle counterparts. We investigate the effects of detrending the RV data by 2 different methods - a Gaussian Process, and a Gaussian filter. We further fit Keplerian orbits to the RV data with periods informed by our GLS and MPSE plots, and optimize via a Markov-Chain Monte Carlo (MCMC) simulation. Using the stellar activity markers Hα and S-index, we confirm prior estimates of the 55 Cnc magnetic cycle. We also confirm the 5 previously discovered planets, while using both a novel periodogram estimator and Gaussian filter detrending technique. Spectral window analysis demonstrates that the MPSE suppresses an order of magnitude of power at the frequency of the lunar artifact, making it less biased from observation cadences correlated with the lunar cycle. This correlation is often unavoidable for ground-based RV observations. Overall, our MPSEs exhibit improved conditions for the identification of planetary signals over the GLS, and we emphasize its reduced susceptibility to false-positive planet detections.