The HD 93963 A transiting system: A 1.04d super-Earth and a 3.65 d sub-Neptune discovered by TESS and CHEOPS

Abstract

We present the discovery of two small planets transiting HD 93963A (TOI-1797), a G0\,V star (M${}_{\ast }$=1.109\,$\pm$\,0.043\,M${}_{\odot }$, R${}_{\ast }$=1.043\,$\pm$\,0.009\,R${}_{\odot }$) in a visual binary system. We combined TESS and CHEOPS space-borne photometry with data from MuSCAT 2, `Alopeke, PHARO, TRES, FIES, and SOPHIE. We validated and spectroscopically confirmed the outer transiting planet HD 93963 Ac, a sub-Neptune with an orbital period of P${}_c\approx$ 3.65 d, reported as a TESS object of interest (TOI) shortly after the release of Sector 22 data. HD 93963 Ac has a mass of M${}_c=19.2\pm 4.1$ M${}_{\oplus }$ and a radius of R${}_c=3.228\pm 0.059$ R${}_{\oplus }$, implying a mean density of ${\rho }_c=3.1\pm 0.7$ gcm${}^{-3}$. The inner object, HD 93963 Ab, is a validated 1.04 d ultra-short period (USP) transiting super-Earth that we discovered in the TESS light curve and that was not listed as a TOI, owing to the low significance of its signal (TESS signal-to-noise ratio $\approx$ 6.7, TESS $+$ CHEOPS combined transit depth D${}_b=141.5\pm 8.5$ ppm). We intensively monitored the star with CHEOPS by performing nine transit observations to confirm the presence of the inner planet and validate the system. HD 93963 Ab is the first small (R${}_b=1.35\pm 0.042$ R${}_{\oplus }$) USP planet discovered and validated by TESS and CHEOPS. Unlike planet c, HD 93963 Ab is not significantly detected in our radial velocities (M${}_b=7.8\pm 3.2$ M${}_{\oplus }$). We also discovered a linear trend in our Doppler measurements, suggesting the possible presence of a long-period outer planet. With a V-band magnitude of 9.2, HD 93963 A is among the brightest stars known to host a USP planet, making it one of the most favourable targets for precise mass measurement via Doppler spectroscopy and an important laboratory to test formation, evolution, and migration models of planetary systems hosting ultra-short period planets.

Accepted in Astronomy & Astrophysics

References in corpus (61)

• The Transiting Exoplanet Survey Satellite
• The generalised Lomb-Scargle periodogram. A new formalism for the floating-mean and Keplerian periodograms
• The K2 Mission: Characterization and Early results
• galpy: A Python Library for Galactic Dynamics
• Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics
• Gaia Early Data Release 3: Parallax bias versus magnitude, colour, and position
• ESPRESSO@VLT -- On-sky performance and first results
• Planets and Stellar Activity: Hide and Seek in the CoRoT-7 system
• The TESS Objects of Interest Catalog from the TESS Prime Mission
• Three regimes of extrasolar planets inferred from host star metallicities
• A new code for automatic determination of equivalent widths: Automatic Routine for line Equivalent widths in stellar Spectra (ARES)
• Precision Stellar Characterization of FGKM Stars using an Empirical Spectral Library
• The CHEOPS mission
• SOAP 2.0: A tool to estimate the photometric and radial velocity variations induced by stellar spots and plages
• The Kepler Follow-Up Observation Program. I. A Catalog of Companions to Kepler Stars from High-Resolution Imaging
• CLES, Code Liegeois d'Evolution Stellaire
• Determining stellar macroturbulence using asteroseismic rotational velocities from Kepler
• A Study of the Shortest-Period Planets Found With Kepler
• Transit Least Squares: Optimized transit detection algorithm to search for periodic transits of small planets
• Revisited Mass-Radius relations for exoplanets below 120 Earth masses
• Stellar Winds on the Main-Sequence II: the Evolution of Rotation and Winds
• ARES v2 - new features and improved performance
• A generalized bayesian inference method for constraining the interiors of super Earths and sub-Neptunes
• Six transiting planets and a chain of Laplace resonances in TOI-178
• A Statistical Reconstruction of the Planet Population Around Kepler Solar-Type Stars
• Vetting of 384 TESS Objects of Interest with TRICERATOPS and Statistical Validation of 12 Planet Candidates
• Transiting extrasolar planetary candidates in the Galactic bulge
• Revising the ages of planet-hosting stars
• A remnant planetary core in the hot-Neptune desert
• A Spectroscopic Analysis of the California-Kepler Survey Sample: I. Stellar Parameters, Planetary Radii and a Slope in the Radius Gap
• The hot dayside and asymmetric transit of WASP-189b seen by CHEOPS
• pyaneti II: A multidimensional Gaussian process approach to analysing spectroscopic time-series
• Constraining planet structure and composition from stellar chemistry: trends in different stellar populations
• A Super-Solar Metallicity For Stars With Hot Rocky Exoplanets
• Speckle Observations of TESS Exoplanet Host Stars. II. Stellar Companions at 1-1000 AU and Implications for Small Planet Detection
• Transit detection of the long-period volatile-rich super-Earth ${\nu }^2$ Lupi d with $CHEOPS$
• An Ultra-Hot Neptune in the Neptune desert
• CHEOPS observations of the HD 108236 planetary system: A fifth planet, improved ephemerides, and planetary radii
• Analysis of Early Science observations with the CHaracterising ExOPlanets Satellite (CHEOPS) using pycheops
• The transiting multi-planet system HD3167: a 5.7 MEarth Super-Earth and a 8.3 MEarth mini-Neptune
• The Habitable-zone Planet Finder Reveals A High Mass and a Low Obliquity for the Young Neptune K2-25b
• Hydrogen dominated atmospheres on terrestrial mass planets: evidence, origin and evolution
• WASP-186 and WASP-187: two hot Jupiters discovered by SuperWASP and SOPHIE with additional observations by TESS
• Speckle Imaging Excludes Low-Mass Companions Orbiting the Exoplanet Host Star TRAPPIST-1
• A pair of Sub-Neptunes transiting the bright K-dwarf TOI-1064 characterised with CHEOPS
• An unusually low density ultra-short period super-Earth and three mini-Neptunes around the old star TOI-561
• Reinvestigating $\alpha$ Cen AB in light of asteroseismic forward and inverse methods
• Kepler423b: a half-Jupiter mass planet transiting a very old solar-like star
• A study of the performance of the transit detection tool DST in space-based surveys. Application of the CoRoT pipeline to Kepler data
• CHEOPS Precision Phase Curve of the Super-Earth 55 Cnc e
• A planetary system with two transiting mini-Neptunes near the radius valley transition around the bright M dwarf TOI-776
• The Transiting Multi-planet System HD15337: Two Nearly Equal-mass Planets Straddling the Radius Gap
• Gaia Search for stellar Companions of TESS Objects of Interest II
• The misaligned orbit of the Earth-sized planet Kepler-408b
• Transits of Known Planets Orbiting a Naked-Eye Star
• A transit survey to search for planets around hot subdwarfs: I. methods and performance tests on light curves from Kepler, K2, TESS, and CHEOPS
• TOI-132 b: A short-period planet in the Neptune desert transiting a $V=11.3$ G-type star
• The EBLM project -- VIII. First results for M-dwarf mass, radius and effective temperature measurements using CHEOPS light curves
• A low-eccentricity migration pathway for a 13-h-period Earth analogue in a four-planet system
• TESS discovery of a super-Earth and three sub-Neptunes hosted by the bright, Sun-like star HD 108236
• Composition of super-Earths, super-Mercuries, and their host stars

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