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 K2 photometry in Campaigns 5 and 16, transiting a bright star (V_(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 2σ detection of a sub-Saturn planet. The confirmed planet has a radius of 6.12 ± 0.1 R⊕, and a mass of 27^(+14)_(-12.6) M⊕. We also place an upper limit on the mass (within the 3σ confidence interval) at 42 M⊕ above the nominal value. This results in the Saturn-like density of 0.65^(+0.34)_(-0.30) 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 and 70 M⊕ and radii between 4 and 8 R⊕, whose masses and radii are measured to a precision of 50% or better (only 23 including this work).

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