HD 76920b pinned down: a detailed analysis of the most eccentric planetary system around an evolved star

Abstract

We present 63 new multi-site radial velocity measurements of the K1III giant HD 76920, which was recently reported to host the most eccentric planet known to orbit an evolved star. We focussed our observational efforts on the time around the predicted periastron passage and achieved near-continuous phase coverage of the corresponding radial velocity peak. By combining our radial velocity measurements from four different instruments with previously published ones, we confirm the highly eccentric nature of the system, and find an even higher eccentricity of $e=0.8782\pm 0.0025$, an orbital period of $415.891_{-0.039}^{+0.043}\mathrm{d}$, and a minimum mass of $3.13_{-0.43}^{+0.41}{\mathrm{M}}_{\mathrm{J}}$ for the planet. The uncertainties in the orbital elements are greatly reduced, especially for the period and eccentricity. We also performed a detailed spectroscopic analysis to derive atmospheric stellar parameters, and thus the fundamental stellar parameters ($M_{\ast },R_{\ast },L_{\ast }$), taking into account the parallax from Gaia DR2, and independently determined the stellar mass and radius using asteroseismology. Intriguingly, at periastron the planet comes to within 2.4 stellar radii of its host star's surface. However, we find that the planet is not currently experiencing any significant orbital decay and will not be engulfed by the stellar envelope for at least another $50-80$ Myr. Finally, while we calculate a relatively high transit probability of $16\%$, we did not detect a transit in the TESS photometry.

15 pages, 12 figures, 5 tables, accepted for publication in PASA

References in corpus (19)

• Dynamical Outcomes of Planet-Planet Scattering
• Retired A Stars and Their Companions: Exoplanets Orbiting Three Intermediate-Mass Subgiants
• CERES: A Set of Automated Routines for Echelle Spectra
• Hot Jupiters and Cool Stars
• Efficient fitting of multiplanet Keplerian models to radial velocity and astrometry data
• On the Eccentricity Distribution of Exoplanets from Radial Velocity Surveys
• Accounting for velocity jitter in planet search surveys
• A Planetary Mass Companion to the K0 Giant HD 17092
• High eccentricity planets from the Anglo-Australian Planet Search
• Constraining Orbital Parameters Through Planetary Transit Monitoring
• Kepler-432: a red giant interacting with one of its two long period giant planets
• Selection Functions in Doppler Planet Searches
• The Pan-Pacific Planet Search VII: The most eccentric planet orbiting a giant star
• Determination Of The Orbit Of The Planetary Companion To The Metal Rich Star HD 45350
• Truly eccentric. I. Revisiting eight single-eccentric planetary systems
• The Pan-Pacific Planet Search VI: Giant planets orbiting HD 86950 and HD 222076
• Was Planet 9 captured in the Sun's natal star-forming region?
• Truly eccentric. II. When can two circular planets mimic a single eccentric orbit?
• Which Radial Velocity Exoplanets Have Undetected Outer Companions?

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• An Edge-On Orbit for the Eccentric Long-Period Planet HR 5183 b
• TESS Asteroseismic Analysis of HD 76920: The Giant Star Hosting An Extremely Eccentric Exoplanet
• Companions to Kepler giant stars: A long-period eccentric substellar companion to KIC 3526061 and a stellar companion to HD 187878
• Asteroseismology of iota Draconis and Discovery of an Additional Long-Period Companion