Abstract
We present the discovery and characterization of a transiting sub-Neptune that orbits the nearby (28 pc) and bright (V = 8.37) K0V star HD 207897 (TOI-1611) with a 16.20-day period. This discovery is based on photometric measurements from the Transiting Exoplanet Survey Satellite mission and radial velocity (RV) observations from the SOPHIE, Automated Planet Finder, and HIRES high-precision spectrographs. We used EXOFASTv2 to model the parameters of the planet and its host star simultaneously, combining photometric and RV data to determine the planetary system parameters. We show that the planet has a radius of 2.50 ± 0.08 RE and a mass of either 14.4 ± 1.6 ME or 15.9 ± 1.6 ME with nearly equal probability. The two solutions correspond to two possibilities for the stellar activity period. The density accordingly is either 5.1 ± 0.7 g cm−3 or 5.5−0.7+0.8 g cm−3, making it one of the relatively rare dense sub-Neptunes. The existence of this dense planet at only 0.12 AU from its host star is unusual in the currently observed sub-Neptune (2 < RE < 4) population. The most likely scenario is that this planet has migrated to its current position.
Highlights
The brightness of more than 200,000 stars has been monitored by Transiting Exoplanet Survey Satellite (TESS) (Ricker et al 2015) with 2 minutes cadence during its twoyear primary mission
The SOPHIE data were reduced with the SOPHIE Data Reduction pipeline (DRS, Bouchy et al 2009b), which extracts the radial velocity (RV) by cross-correlating spectrum with a binary mask and doing a Gaussian fit of the cross-correlation function (CCF) (Pepe et al 2002)
Adopting the value of the RV jitter of 3.16 m s−1, we find that the hypothesis that the phase and amplitude of the 37.6-day signal is constant is rejected at 2σ, which further supports the hypothesis that this signal is due to activity
Summary
The brightness of more than 200,000 stars has been monitored by TESS (Ricker et al 2015) with 2 minutes cadence during its twoyear primary mission. The observed stars are closer and brighter (typically 30-100 times brighter) than the stars Kepler surveyed This offers us a unique opportunity for furthering our knowledge in planetary science with follow-up observations: those from ground-based high precision spectrographs to confirm the planetary nature and mass measurement, which with the radius allows us to determine the bulk composition of planets; and ground and space-based observations to provide atmospheric characterization, for instance, with the upcoming James Webb Space Telescope (Gardner et al 2006). We announce the detection and characterization of a sub-Neptune orbiting a bright (V=8.4) K0 star using TESS photometric data and SOPHIE, APF, and HIRES RVs. In Sect.
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