Three planets transiting the evolved star EPIC 249893012: a hot 8.8-M${}_{\oplus }$ super-Earth and two warm 14.7 and 10.2-M${}_{\oplus }$ sub-Neptunes

Abstract

We report the discovery of a new planetary system with three transiting planets, one super-Earth and two sub-Neptunes, that orbit EPIC\,249893012, a G8\,IV-V evolved star ($M_{\star }$\,=\,1.05\,$\pm$\,0.05\,$M_{\odot }$, $R_{\star }$\,=\,1.71\,$\pm$\,0.04\,$R_{\odot }$, $T_{\mathrm{eff}}$\,=5430\,$\pm$\,85\,K). The star is just leaving the main sequence. We combined \ktwo \ photometry with IRCS adaptive-optics imaging and HARPS, HARPS-N, and CARMENES high-precision radial velocity measurements to confirm the planetary system, determine the stellar parameters, and measure radii, masses, and densities of the three planets. With an orbital period of $3.5949_{-0.0007}^{+0.0007}$ days, a mass of $8.75_{-1.08}^{+1.09}{M}_{\oplus }$ , and a radius of $1.95_{-0.08}^{+0.09}{R}_{\oplus }$, the inner planet b is compatible with nickel-iron core and a silicate mantle (${\rho }_b=6.39_{-1.04}^{+1.19}$ g cm${}^{-3}$). Planets c and d with orbital periods of $15.624_{-0.001}^{+0.001}$ and $35.747_{-0.005}^{+0.005}$ days, respectively, have masses and radii of $14.67_{-1.89}^{+1,84}{M}_{\oplus }$ and $3.67_{-0.14}^{+0.17}{R}_{\oplus }$ and $10.18_{-2.42}^{+2.46}{M}_{\oplus }$ and $3.94_{-0.12}^{+0.13}{R}_{\oplus }$, respectively, yielding a mean density of $1.62_{-0.29}^{+0.30}$ and $0.91_{-0.23}^{+0.25}$ g cm${}^{-3}$, respectively. The radius of planet b lies in the transition region between rocky and gaseous planets, but its density is consistent with a rocky composition. Its semimajor axis and the corresponding photoevaporation levels to which the planet has been exposed might explain its measured density today. In contrast, the densities and semimajor axes of planets c and d suggest a very thick atmosphere. The singularity of this system, which orbits a slightly evolved star that is just leaving the main sequence, makes it a good candidate for a deeper study from a dynamical point of view.

arXiv commentAccepted for publication in A\& A

References in corpus (72)

• Gaia Data Release 2. Summary of the contents and survey properties
• Modules for Experiments in Stellar Astrophysics (MESA)
• The Transiting Exoplanet Survey Satellite
• Intrinsic Colors, Temperatures, and Bolometric Corrections of Pre-Main Sequence Stars
• Analytic Lightcurves for Planetary Transit Searches
• Estimating distances from parallaxes IV: Distances to 1.33 billion stars in Gaia Data Release 2
• The generalised Lomb-Scargle periodogram. A new formalism for the floating-mean and Keplerian periodograms
• The K2 Mission: Characterization and Early results
• The California-Kepler Survey. III. A Gap in the Radius Distribution of Small Planets
• Accurate masses and radii of normal stars: modern results and applications
• The PLATO 2.0 Mission
• batman: BAsic Transit Model cAlculatioN in Python
• Planetary Radii across Five Orders of Magnitude in Mass and Stellar Insolation: Application to Transits
• A box-fitting algorithm in the search for periodic transits
• Efficient, uninformative sampling of limb darkening coefficients for two-parameter laws
• The NASA Exoplanet Archive: Data and Tools for Exoplanet Research
• Kepler Input Catalog: Photometric Calibration and Stellar Classification
• The CoRoT satellite in flight : description and performance
• Kepler planets: a tale of evaporation
• Gaia Data Release 2: Photometric content and validation
• Gaia Data Release 2: using Gaia parallaxes
• Origins of Hot Jupiters
• The CORALIE survey for southern extra-solar planets VII. Two short-period Saturnian companions to HD108147 and HD168746
• A Revised Age for Upper Scorpius and The Star-Formation History Among the F-Type Members of the Scorpius-Centaurus OB Association
• The California Kepler Survey VII. Precise Planet Radii Leveraging Gaia DR2 Reveal the Stellar Mass Dependence of the Planet Radius Gap
• An asteroseismic view of the radius valley: stripped cores, not born rocky
• Masses, Radii, and Orbits of Small Kepler Planets: The Transition from Gaseous to Rocky Planets
• Basic physical parameters of a selected sample of evolved stars
• Galactic Reddening in 3D from Stellar Photometry - An Improved Map
• On the use of empirical bolometric corrections for stars
• Mass-Radius Relation for Rocky Planets based on PREM
• A Gaussian process framework for modelling stellar activity signals in radial velocity data
• Spectroscopy Made Easy: Evolution
• Ages and fundamental properties of Kepler exoplanet host stars from asteroseismology
• Dearth of short-period Neptunian exoplanets - a desert in period-mass and period-radius planes
• Evidence for a systematic offset of -80 micro-arcseconds in the Gaia DR2 parallaxes
• A new list of thorium and argon spectral lines in the visible
• Binning is sinning: morphological light-curve distortions due to finite integration time
• Precision Stellar Characterization of FGKM Stars using an Empirical Spectral Library
• On the use of Gaia magnitudes and new tables of bolometric corrections
• Spitzer Secondary Eclipses of the Dense, Modestly-irradiated, Giant Exoplanet HAT-P-20b Using Pixel-Level Decorrelation
• Make Super-Earths, Not Jupiters: Accreting Nebular Gas onto Solid Cores at 0.1 AU and Beyond
• Lack of Inflated Radii for Kepler Giant Planet Candidates Receiving Modest Stellar Irradiation
• Determining stellar macroturbulence using asteroseismic rotational velocities from Kepler
• Photoevaporation and High-Eccentricity Migration Created the Sub-Jovian Desert
• Atmospheric Mass Loss During Planet Formation: The Importance of Planetesimal Impacts
• Occurrence Rates of Planets orbiting FGK Stars: Combining Kepler DR25, Gaia DR2 and Bayesian Inference
• A Statistical Reconstruction of the Planet Population Around Kepler Solar-Type Stars
• How formation time-scales affect the period dependence of the transition between rocky super-Earths and gaseous sub-Neptunes and implications for ${\eta }_{\oplus }$
• Improved stellar parameters of CoRoT-7
• An update to the EVEREST K2 pipeline: Short cadence, saturated stars, and Kepler-like photometry down to Kp = 15
• TESS's first planet: a super-Earth transiting the naked-eye star $\pi$ Mensae
• Gas giant planets as dynamical barriers to inward-migrating super-Earths
• Pyaneti: a fast and powerful software suite for multi-planet radial velocity and transit fitting
• Exoplanets around Low-mass Stars Unveiled by K2
• The star formation in the L1615/L1616 cometary cloud
• The transiting multi-planet system HD3167: a 5.7 MEarth Super-Earth and a 8.3 MEarth mini-Neptune
• Radial velocity confirmation of K2-100b: a young, highly irradiated, and low density transiting hot Neptune
• K2-141 b: A 5-M${}_{\oplus }$ super-Earth transiting a K7 V star every 6.7 hours
• The CARMENES search for exoplanets around M dwarfs - HD 147379b: A nearby Neptune in the temperate zone of an early-M dwarf
• Super-Earth of 8 Mearth in a 2.2-day orbit around the K5V star K2-216
• The Transiting Multi-planet System HD15337: Two Nearly Equal-mass Planets Straddling the Radius Gap
• EPIC 210894022b - A short period super-Earth transiting a metal poor, evolved old star
• Do close-in giant planets orbiting evolved stars prefer eccentric orbits?
• HD219666b: A hot-Neptune from TESS Sector 1
• The K2-ESPRINT Project III: A Close-in Super-Earth around a Metal-rich Mid-M Dwarf
• K2-98 b: A 32-M${}_{\oplus }$ Neptune-sized planet in a 10-day orbit transiting an F8 star
• Detection and Doppler monitoring of EPIC 246471491, a system of four transiting planets smaller than Neptune
• Mass determination of the 1:3:5 near-resonant planets transiting GJ 9827 (K2-135)
• Detection and characterization of an ultra-dense sub-Neptune planet orbiting the Sun-like star HD 119130
• K2-31b, a grazing transiting hot Jupiter on an 1.26-day orbit around a bright G7V star
• A Gap in the Mass Distribution for Warm Neptune and Terrestrial Planets

Cited by in corpus (11)

• The CARMENES search for exoplanets around M dwarfs. Two planets on the opposite sides of the radius gap transiting the nearby M dwarf LTT 3780
• Caught in the Act: Core-powered Mass-loss Predictions for Observing Atmospheric Escape
• The HD 137496 system: A dense, hot super-Mercury and a cold Jupiter
• Resonant sub-Neptunes are puffier
• Precise mass determination for the keystone sub-Neptune planet transiting the mid-type M dwarf G 9-40
• Exoplanet atmosphere evolution: emulation with neural networks
• Characterisation of TOI-406 as showcase of the THIRSTEE program: A 2-planet system straddling the M-dwarf density gap
• The GALAH Survey: Improving our understanding of confirmed and candidate planetary systems with large stellar surveys
• An Informational-Entropic Approach to Exoplanet Characterization
• The Occurrence-weighted Median Planets Discovered by Transit Surveys Orbiting Solar-type Stars and Their Implications for Planet Formation and Evolution
• The TESS-Keck Survey. XI. Mass Measurements for Four Transiting sub-Neptunes orbiting K dwarf TOI-1246