TESS discovery of a super-Earth and three sub-Neptunes hosted by the bright, Sun-like star HD 108236

Abstract

We report the discovery and validation of four extrasolar planets hosted by the nearby, bright, Sun-like (G3V) star HD~108236 using data from the Transiting Exoplanet Survey Satellite (TESS). We present transit photometry, reconnaissance and precise Doppler spectroscopy as well as high-resolution imaging, to validate the planetary nature of the objects transiting HD~108236, also known as the TESS Object of Interest (TOI) 1233. The innermost planet is a possibly-rocky super-Earth with a period of $3.79523_{-0.00044}^{+0.00047}$ days and has a radius of $1.586\pm 0.098$ $R_{\oplus }$. The outer planets are sub-Neptunes, with potential gaseous envelopes, having radii of $2.068_{-0.091}^{+0.10}$ $R_{\oplus }$, $2.72\pm 0.11$ $R_{\oplus }$, and $3.12_{-0.12}^{+0.13}$ $R_{\oplus }$ and periods of $6.20370_{-0.00052}^{+0.00064}$ days, $14.17555_{-0.0011}^{+0.00099}$ days, and $19.5917_{-0.0020}^{+0.0022}$ days, respectively. With V and K${}_{\mathrm{s}}$ magnitudes of 9.2 and 7.6, respectively, the bright host star makes the transiting planets favorable targets for mass measurements and, potentially, for atmospheric characterization via transmission spectroscopy. HD~108236 is the brightest Sun-like star in the visual (V) band known to host four or more transiting exoplanets. The discovered planets span a broad range of planetary radii and equilibrium temperatures, and share a common history of insolation from a Sun-like star ($R_{\star }=0.888\pm 0.017$ R${}_{\odot }$, $T_{\mathrm{eff}}=5730\pm 50$ K), making HD 108236 an exciting, opportune cosmic laboratory for testing models of planet formation and evolution.

accepted for publication in The Astronomical Journal

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• CHEOPS observations of the HD 108236 planetary system: A fifth planet, improved ephemerides, and planetary radii
• ExoClock Project III: 450 new exoplanet ephemerides from ground and space observations
• The Magellan-TESS Survey I: Survey Description and Mid-Survey Results
• TOI-2257 b: A highly eccentric long-period sub-Neptune transiting a nearby M dwarf
• Exciting the TTV Phases of Resonant Sub-Neptunes
• The HD 93963 A transiting system: A 1.04d super-Earth and a 3.65 d sub-Neptune discovered by TESS and CHEOPS
• Allesfitter: Flexible Star and Exoplanet Inference From Photometry and Radial Velocity
• Characterization of the HD 108236 system with CHEOPS and TESS. Confirmation of a fifth transiting planet
• A Search for Exoplanets in Open Clusters and Young Associations based on TESS Objects of Interest
• NIGHT: a compact, near-infrared, high-resolution spectrograph to survey helium in exoplanet systems
• Observations of scattered light from exoplanet atmospheres
• New models of reflection spectra for terrestrial exoplanets: Present and prebiotic Earth orbiting around stars of different spectral types
• The Visual Survey Group: A Decade of Hunting Exoplanets and Unusual Stellar Events with Space-Based Telescopes