TESS-Keck Survey IX: Masses of Three Sub-Neptunes Orbiting HD 191939 and the Discovery of a Warm Jovian Plus a Distant Sub-Stellar Companion

Abstract

Exoplanet systems with multiple transiting planets are natural laboratories for testing planetary astrophysics. One such system is HD 191939 (TOI-1339), a bright (V=9) and Sun-like (G9V) star, which TESS found to host three transiting planets (b, c, and d). The planets have periods of 9, 29, and 38 days each with similar sizes from 3 to 3.4 $R_{\oplus }$. To further characterize the system, we measured the radial velocity (RV) of HD 191939 over 415 days with Keck/HIRES and APF/Levy. We find that $M_b=10.4\pm 0.9M_{\oplus }$ and $M_c=7.2\pm 1.4M_{\oplus }$, which are low compared to most known planets of comparable radii. The RVs yield only an upper-limit on $M_d$ (<5.8 $M_{\oplus }$ at 2$\sigma$). The RVs further reveal a fourth planet (e) with a minimum mass of $0.34\pm 0.01M_{Jup}$ and an orbital period of 101.4 $\pm$ 0.4 days. Despite its non-transiting geometry, secular interactions between planet e and the inner transiting planets indicate that planet e is coplanar with the transiting planets ($\Delta$i < 10${}^{\circ }$). We identify a second high mass planet (f) with 95% confidence intervals on mass between $2-11M_{Jup}$ and period between 1700-7200 days, based on a joint analysis of RVs and astrometry from $Gaia$ and $Hipparcos$. As a bright star hosting multiple planets with well-measured masses, HD 191939 presents many options for comparative planetary astronomy including characterization with JWST.

20 pages, 10 figures. Accepted for publication in The Astronomical Journal

References in corpus (27)

• The Transiting Exoplanet Survey Satellite
• The generalised Lomb-Scargle periodogram. A new formalism for the floating-mean and Keplerian periodograms
• Gaia Early Data Release 3: The astrometric solution
• Most 1.6 Earth-Radius Planets are not Rocky
• Prospects for the Characterization and Confirmation of Transiting Exoplanets via the Rossiter-McLaughlin Effect
• The Hipparcos-Gaia Catalog of Accelerations: Gaia EDR3 Edition
• Asteroseismology and Gaia: Testing Scaling Relations Using 2200 Kepler Stars with TGAS Parallaxes
• Transit Least Squares: Optimized transit detection algorithm to search for periodic transits of small planets
• Six transiting planets and a chain of Laplace resonances in TOI-178
• Kepler Multi-Planet Systems Exhibit Unexpected Intra-system Uniformity in Mass and Radius
• High-precision abundances of elements in solar-type stars. Evidence of two distinct sequences in abundance-age relations
• WASP-107b's density is even lower: a case study for the physics of planetary gas envelope accretion and orbital migration
• Tidally-Induced Radius Inflation of Sub-Neptunes
• An information theoretic framework for classifying exoplanetary system architectures
• The TESS-Keck Survey IV: A Retrograde, Polar Orbit for the Ultra-Low-Density, Hot Super-Neptune WASP-107b
• An Analytic Criterion for Turbulent Disruption of Planetary Resonances
• The TESS-Keck Survey II: An Ultra-Short Period Rocky Planet and its Siblings Transiting the Galactic Thick-Disk Star TOI-561
• Long-Period Giant Companions to Three Compact, Multiplanet Systems
• The TESS-Keck Survey I: A Warm Sub-Saturn-mass Planet and a Caution about Stray Light in TESS Cameras
• Transmission spectroscopy for the warm sub-Neptune HD3167c: evidence for molecular absorption and a possible high metallicity atmosphere
• The TESS-Keck Survey: Science Goals and Target Selection
• Stellar Characterization of Keck HIRES Spectra with The Cannon
• TKS III: A Stellar Obliquity Measurement of TOI-1726 c
• Long Period Jovian Tilts the Orbits of Two sub-Neptunes Relative to Stellar Spin Axis in Kepler-129
• HD 191939: Three Sub-Neptunes Transiting a Sun-like Star Only 54 pc Away
• TKS V. Twin sub-Neptunes Transiting the Nearby G Star HD 63935
• The California Legacy Survey II. Occurrence of Giant Planets Beyond the Ice line

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• Inner Planetary System Gap Complexity is a Predictor of Outer Giant Planets
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• The TESS-Keck Survey. XV. Precise Properties of 108 TESS Planets and Their Host Stars
• TESS-Keck Survey XIV: Two giant exoplanets from the Distant Giants Survey
• GJ 3929: High Precision Photometric and Doppler Characterization of an Exo-Venus and its Hot, Mini-Neptune-mass Companion
• Exoplanet atmosphere evolution: emulation with neural networks
• Dynamical Architectures of S-type Transiting Planets in Binaries I: Target Selection using Hipparcos and Gaia proper motion anomalies
• exoMMR: a New Python Package to Confirm and Characterize Mean Motion Resonances
• TOI-1696 and TOI-2136: Constraining the Masses of Two Mini-Neptunes with HPF
• A Transiting Super-Earth in the Radius Valley and An Outer Planet Candidate Around HD 307842
• Homogeneous planet masses I: Reanalysis of archival HARPS radial velocities
• Dynamical Architectures of S-type Transiting Planets in Binaries II: A Dichotomy in Orbital Alignment of Small Planets in Close Binary Systems
• The TESS-Keck Survey. XIX. A Warm Transiting Sub-Saturn Mass Planet and a non-Transiting Saturn Mass Planet Orbiting a Solar Analog
• An adaptive optics upgrade for the Automated Planet Finder Telescope using an adaptive secondary mirror