The K2 & TESS Synergy II: Revisiting 26 systems in the TESS Primary Mission

TL;DR

This study revisits 26 K2-discovered exoplanet systems using combined K2 and TESS data to refine their parameters and improve transit ephemerides, aiding future observational efforts.

Contribution

It provides updated system parameters for 26 exoplanets by jointly analyzing K2 and TESS lightcurves, enhancing transit predictions for future studies.

Findings

Refined ephemerides for 23 systems with detectable TESS transits.

Updated stellar parameters using Gaia, SED, and MIST models.

Provided system parameters for 13 systems without TESS-detectable transits.

Abstract

The legacy of NASA's K2 mission has provided hundreds of transiting exoplanets that can be revisited by new and future facilities for further characterization, with a particular focus on studying the atmospheres of these systems. However, the majority of K2-discovered exoplanets have typical uncertainties on future times of transit within the next decade of greater than four hours, making observations less practical for many upcoming facilities. Fortunately, NASA's Transiting exoplanet Survey Satellite (TESS) mission is reobserving most of the sky, providing the opportunity to update the ephemerides for $\sim$300 K2 systems. In the second paper of this series, we reanalyze 26 single-planet, K2-discovered systems that were observed in the TESS primary mission by globally fitting their K2 and TESS lightcurves (including extended mission data where available), along with any archival radial velocity measurements. As a result of the faintness of the K2 sample, 13 systems studied here do not have transits detectable by TESS. In those cases, we re-fit the K2 lightcurve and provide updated system parameters. For the 23 systems with $M_* \gtrsim 0.6 M_\odot$, we determine the host star parameters using a combination of Gaia parallaxes, Spectral Energy Distribution (SED) fits, and MESA Isochrones and Stellar Tracks (MIST) stellar evolution models. Given the expectation of future TESS extended missions, efforts like the K2 & TESS Synergy project will ensure the accessibility of transiting planets for future characterization while leading to a self-consistent catalog of stellar and planetary parameters for future population efforts.