Non-radial oscillations mimicking a brown dwarf orbiting the cluster giant NGC 4349 No. 127

Abstract

Several evolved stars have been found to exhibit long-period radial velocity variations that cannot be explained by planetary or brown dwarf companions. Non-radial oscillations caused by oscillatory convective modes have been put forth as an alternative explanation, but no modeling attempt has yet been undertaken. We provide a model of a non-radial oscillation, aiming to explain the observed variations of the cluster giant NGC 4349 No. 127. The star was previously reported to host a brown dwarf companion, but whose existence was later refuted in the literature. We reanalyzed 58 archival HARPS spectra, acquiring additional activity indicators using the SERVAL and RACCOON pipelines. We searched for periodicity in the indicators and correlations between the indicators and radial velocities. We further present a simulation code able to produce synthetic HARPS spectra, incorporating the effect of non-radial oscillations, and compare the simulated results to the observed variations. We find a positive correlation between chromatic index and radial velocity, along with closed-loop Lissajous-like correlations between radial velocity and each of the spectral line shape indicators (full width at half maximum, and contrast of the cross-correlation function and differential line width). Simulations of a low-amplitude, retrograde, dipole (l = 1, m = 1), non-radial oscillation can reproduce the observed behavior and explain the observables. Photometric variations below the detection threshold of the available ASAS-3 photometry are predicted. The oscillation and stellar parameters are largely in agreement with the prediction of oscillatory convective modes. The periodic variations of the radial velocities and activity indicators, along with the respective phase shifts, measured for the intermediate-mass cluster giant NGC 4349 No. 127, can be explained by a non-radial oscillation.

23 pages, 14 figures. Accepted in A&A. Abstract abridged for arXiv submission

References in corpus (36)

• 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
• The K2 Mission: Characterization and Early results
• Spectrum radial velocity analyser (SERVAL). High-precision radial velocities and two alternative spectral indicators
• Improving the open cluster census. II. An all-sky cluster catalogue with Gaia DR3
• 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
• Precise radial velocities of giant stars. III. Spectroscopic stellar parameters
• Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia EDR3 stars brighter than G=18.5
• Planets around evolved intermediate-mass stars. I. Two substellar companions in the open clusters NGC 2423 and NGC 4349
• Gaia Data Release 3: Astrophysical parameters inference system (Apsis) I -- methods and content overview
• Improving the open cluster census. III. Using cluster masses, radii, and dynamics to create a cleaned open cluster catalogue
• Extrasolar planets and brown dwarfs around A-F type stars VI. High precision RV survey of early type dwarfs with HARPS
• The Magnetic Fields at the Surface of Active Single G-K Giants
• 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
• RASSINE: Interactive tool for normalising stellar spectra I. Description and performance of the code
• 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 CARMENES search for exoplanets around M dwarfs. Mapping stellar activity indicators across the M dwarf domain
• The CARMENES search for exoplanets around M dwarfs: Convective shift and starspot constraints from chromatic radial velocities
• The CARMENES search for exoplanets around M dwarfs: Benchmarking the impact of activity in high-precision radial velocity measurements
• 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
• SOAP-GPU: Efficient Spectral Modelling of Stellar Activity Using Graphical Processing Units
• Search for lithium-rich giants in 32 open clusters with high-resolution spectroscopy
• Regular Radial Velocity Variations in Nine G- and K-type Giant Stars: Eight Planets and One Planet Candidate
• Rotational splitting and asteroseismic modelling of the delta Scuti star EE Camelopardalis
• Long Secondary Periods in luminous red giant variables
• Planets around evolved intermediate-mass stars III. Planet candidates and long-term activity signals in six open clusters
• Precise radial velocities of giant stars XV. Mysterious nearly periodic radial velocity variations in the eccentric binary $\epsilon$ Cygni
• Surface magnetism in the pulsating RV Tauri star R Scuti
• Tracking Advanced Planetary Systems (TAPAS) with HARPS-N VII. Elder suns with low-mass companions
• Search for Exoplanets around Northern Circumpolar Stars V. Three likely planetary companions to the giant stars HD 19615, HD 150010, and HD 174205

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