Precise radial velocities of giant stars -- XVII. Distinguishing planets from intrinsically induced radial velocity signals in evolved stars

Abstract

From a long-term Doppler monitoring campaign of 373 giant stars, we have identified ten giants with periodic radial velocity variations that are challenging to associate with planets. Similar cases in the literature are attributed to poorly understood intrinsic processes. Our goal is to confirm or refute the presence of planets around these ten evolved stars. Additionally, we evaluate the reliability and sensitivity of planet-confirmation metrics when applied to giant stars and present cases of intrinsically induced radial velocity variations, aiming to enhance the physical understanding of the phenomenon. We combined 25 years of radial velocity data from the Hamilton/Lick, SONG, and CARMENES spectrographs. To assess consistency with Keplerian models, we examined the residuals and tracked changes in statistical significance as new data were incorporated. Additionally, we compared radial velocity amplitudes across optical and infrared wavelengths, searched for periodic variations of activity indicators, and examined their correlations with radial velocities. Seven of the ten giants exhibit intrinsically induced radial velocity variations. The strongest arguments against planets orbiting the giants are guided by long-term radial velocity monitoring that detects changing periodicity on long timescales or detects systematics close to the original period in the radial velocity residuals. While activity indicators offer some support, their signals are generally weak. Comparing optical and infrared radial velocity amplitudes also proves insufficient for confirming or refuting planets. We find HIP 64823 remains a promising candidate for hosting a giant exoplanet with orbital period $P\sim$ 7.75 yr. For two stars, the evidence remains inconclusive. Long-term radial velocity monitoring is essential for distinguishing planetary companions from intrinsic variations in evolved stars.

23 pages, 11 figures, 4 appendices, Accepted for publication in Astronomy & Astrophysics, Abstract abridged for arXiv submission

References in corpus (54)

• Array Programming with NumPy
• The Gaia mission
• Gaia Data Release 3: Summary of the content and survey properties
• The generalised Lomb-Scargle periodogram. A new formalism for the floating-mean and Keplerian periodograms
• Bayes in the sky: Bayesian inference and model selection in cosmology
• astroquery: An Astronomical Web-Querying Package in Python
• Spectrum radial velocity analyser (SERVAL). High-precision radial velocities and two alternative spectral indicators
• Stellar Activity Masquerading as Planets in the Habitable Zone of the M dwarf Gliese 581
• Retired A Stars and Their Companions: Exoplanets Orbiting Three Intermediate-Mass Subgiants
• Precise Radial Velocities of Giant Stars VII. Occurrence Rate of Giant Extrasolar Planets as a Function of Mass and Metallicity
• TW Hydrae: evidence of stellar spots instead of a Hot Jupiter
• Precise radial velocities of giant stars. III. Spectroscopic stellar parameters
• Planets around evolved intermediate-mass stars. I. Two substellar companions in the open clusters NGC 2423 and NGC 4349
• Stellar activity of planetary host star HD 189733
• Search for exoplanets with the radial-velocity technique: quantitative diagnostics of stellar activity
• BGLS: A Bayesian formalism for the generalised Lomb-Scargle periodogram
• Confirmation of the Planet Hypothesis for the Long-period Radial Velocity Variations of Beta Geminorum
• Extrasolar planets and brown dwarfs around A-F type stars VI. High precision RV survey of early type dwarfs with HARPS
• The CARMENES search for exoplanets around M dwarfs. Activity indicators at visible and near-infrared wavelengths
• First Results From The Hertzsprung Song Telescope: Asteroseismology Of The G5 Subgiant Star {\Mu}Her
• The CARMENES search for exoplanets around M dwarfs. Guaranteed time observations Data Release 1 (2016-2020)
• The CARMENES search for exoplanets around M dwarfs. Radial velocities and activity indicators from cross-correlation functions with weighted binary masks
• 30 to 100-kG magnetic fields in the cores of red giant stars
• Precise radial velocities of giant stars: I. Stable stars
• Precise radial velocities of giant stars. IV. A correlation between surface gravity and radial velocity variation and a statistical investigation of companion properties
• A Substellar Companion to the Intermediate-Mass Giant 11 Com
• The lithium abundances for a large sample of red giants
• The Na I D resonance lines in main sequence late-type stars
• Strong magnetic fields detected in the cores of 11 red giant stars using gravity-mode period spacings
• The Ca II infrared triplet's performance as an activity indicator compared to Ca II H and K
• Lithium in red giant stars: Constraining non-standard mixing with large surveys in the Gaia era
• Precise radial velocities of giant stars XVI. Planet occurrence rates from the combined analysis of the Lick, EXPRESS, and PPPS giant star surveys
• Binarity as the Origin of Long Secondary Periods in Red Giant Stars
• The Fifth Catalogue of Nearby Stars (CNS5)
• The Discovery of Stellar Oscillations in the K Giant $\iota$ Dra
• Conducting the SONG: The robotic nature and efficiency of a fully automated telescope
• Precise radial velocities of giant stars. XII. Evidence against the proposed planet Aldebaran b
• The Light Curve Shapes as a Key to Resolving the Origin of Long Secondary Periods in Red Giant Stars
• Precise radial velocities of giant stars IX. HD 59686 Ab: a massive circumstellar planet orbiting a giant star in a ~13.6 au eccentric binary system
• The CARMENES search for exoplanets around M dwarfs. Telluric absorption corrected high S/N optical and near-infrared template spectra of 382 M dwarf stars
• Gaussian processes for radial velocity modeling Better rotation periods and planetary parameters with the quasi-periodic kernel and constrained priors
• The Active Chromospheres of Lithium-Rich Red Giant Stars
• Precise radial velocities of giant stars. XI. Two brown dwarfs in 6:1 mean motion resonance around the K giant star $\nu$ Ophiuchi
• Revisiting the Red-giant Branch Hosts KOI-3886 and $\iota$ Draconis. Detailed Asteroseismic Modeling and Consolidated Stellar Parameters
• Magnetic activity of red giants: correlation between the amplitude of solar-like oscillations and chromospheric indicators
• The CARMENES search for exoplanets around M dwarfs. Revisiting the GJ 581 multi-planetary system with new Doppler measurements from CARMENES, HARPS, and HIRES
• Planets around evolved intermediate-mass stars III. Planet candidates and long-term activity signals in six open clusters
• Pollux: A weak dynamo-driven dipolar magnetic field and implications for its probable planet
• The enigma of Li-rich giants and its relation with temporal variations observed in radial velocity and stellar activity signals
• Precise radial velocities of giant stars XV. Mysterious nearly periodic radial velocity variations in the eccentric binary $\epsilon$ Cygni
• Non-radial oscillations mimicking a brown dwarf orbiting the cluster giant NGC 4349 No. 127
• Pyodine: An open, flexible reduction software for iodine-calibrated precise radial velocities
• A Close-in Planet Orbiting Giant Star HD 167768
• A High Resolution Spectrograph for the 72 cm Waltz Telescope at Landessternwarte, Heidelberg

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