Evidence of a Sub-Saturn around EPIC~211945201

Abstract

We report here strong evidence for a sub-Saturn around EPIC~211945201 and confirm its planetary nature. EPIC~211945201b was found to be a planetary candidate from {\it K2} photometry in Campaigns 5 \& 16, transiting a bright star ($V_{\mathrm{mag}}=10.15$, G0 spectral type) in a 19.492 day orbit. However, the photometric data combined with false positive probability calculations using VESPA was not sufficient to confirm the planetary scenario. Here we present high-resolution spectroscopic follow-up of the target using the PARAS spectrograph (19 radial velocity observations) over a time-baseline of 420 days. We conclusively rule out the possibility of an eclipsing binary system and confirm the 2-$\sigma$ detection of a sub-Saturn planet. The confirmed planet has a radius of 6.12$\pm 0.1$$R_{\oplus }$, and a mass of $27_{-12.6}^{+14}$~$M_{\oplus }$. We also place an upper limit on the mass (within the 3-$\sigma$ confidence interval) at 42~$M_{\oplus }$ above the nominal value. This results in the Saturn-like density of $0.65_{-0.30}^{+0.34}$ g~cm${}^{-3}$. Based on the mass and radius, we provide a preliminary model-dependent estimate that the heavy element content is 60-70 \% of the total mass. This detection is important as it adds to a sparse catalog of confirmed exoplanets with masses between 10-70 $M_{\oplus }$ and radii between 4-8 $R_{\oplus }$, whose masses and radii are measured to a precision of 50\% or better (only 23 including this work).

Accepted for publication in The Astronomical Journal, 17 pages, 8 figures