The CARMENES search for exoplanets around M dwarfs: Stable radial-velocity variations at the rotation period of AD~Leonis -- A test case study of current limitations to treating stellar activity

Abstract

Context: A challenge with radial-velocity (RV) data is disentangling the origin of signals either due to a planetary companion or to stellar activity. In fact, the existence of a planetary companion has been proposed, as well as contested, around the relatively bright, nearby M3.0V star AD Leo at the same period as the stellar rotation of 2.23d. Aims: We further investigate the nature of this signal. We introduce new CARMENES optical and near-IR RV data and an analysis in combination with archival data taken by HIRES and HARPS, along with more recent data from HARPS-N, GIANO-B, and HPF. Also, we address the confusion concerning the binarity of AD Leo. Methods: We consider possible correlations between the RVs and various stellar activity indicators accessible with CARMENES. We applied models within a Bayesian framework to determine whether a Keplerian model, a red-noise quasi-periodic model using a Gaussian process, or a mixed model would explain the observed data best. We also exclusively focus on spectral lines potentially associated with stellar activity. Results: The CARMENES RV data agree with the previously reported periodicity of 2.23d, correlate with some activity indicators, and exhibit chromaticity. However, when considering the entire RV data set, we find that a mixed model composed of a stable and a variable component performs best. Moreover, when recomputing the RVs using only spectral lines insensitive to activity, there appears to be some residual power at the period of interest. We therefore conclude that it is not possible to determinedly prove that there is no planet orbiting in synchronization with the stellar rotation given our data, current tools, machinery, and knowledge of how stellar activity affects RVs. We do rule out planets more massive than 27M_E (=0.084M_J). We also exclude any binary companion around AD Leo with Msini > 3-6M_J on orbital periods <14yr.

27 pages, 11 figures

References in corpus (57)

• The generalised Lomb-Scargle periodogram. A new formalism for the floating-mean and Keplerian periodograms
• A terrestrial planet candidate in a temperate orbit around Proxima Centauri
• Bayes in the sky: Bayesian inference and model selection in cosmology
• How to Constrain Your M Dwarf: measuring effective temperature, bolometric luminosity, mass, and radius
• Planets and Stellar Activity: Hide and Seek in the CoRoT-7 system
• Spectrum radial velocity analyser (SERVAL). High-precision radial velocities and two alternative spectral indicators
• Radial velocity planets de-aliased. A new, short period for Super-Earth 55 Cnc e
• Trumpeting M Dwarfs with CONCH-SHELL: a Catalog of Nearby Cool Host-Stars for Habitable ExopLanets and Life
• SOAP 2.0: A tool to estimate the photometric and radial velocity variations induced by stellar spots and plages
• The HARPS search for southern extra-solar planets. X. A m sin i = 11 Mearth planet around the nearby spotted M dwarf GJ 674
• Search for exoplanets with the radial-velocity technique: quantitative diagnostics of stellar activity
• The CARMENES search for exoplanets around M dwarfs: Different roads to radii and masses of the target stars
• CARMENES input catalogue of M dwarfs. I. Low-resolution spectroscopy with CAFOS
• Magnetic activity in the HARPS M-dwarf sample. The rotation-activity relationship for very low-mass stars through R'HK
• Magnetism, rotation, and nonthermal emission in cool stars -- Average magnetic field measurements in 292 M dwarfs
• SPIRou: nIR velocimetry & spectropolarimetry at the CFHT
• BGLS: A Bayesian formalism for the generalised Lomb-Scargle periodogram
• A candidate short-period sub-Earth orbiting Proxima Centauri
• Accounting for velocity jitter in planet search surveys
• Revisiting Proxima with ESPRESSO
• UV habitable zones around M stars
• Stellar activity mimics a habitable-zone planet around Kapteyn's star
• The CARMENES search for exoplanets around M dwarfs. Activity indicators at visible and near-infrared wavelengths
• The CARMENES search for exoplanets around M dwarfs. Stellar atmospheric parameters of target stars with SteParSyn
• Measuring precise radial velocities on individual spectral lines : II. Dependance of stellar activity signal on line depth
• Warm terrestrial planet with half the mass of Venus transiting a nearby star
• CARMENES input catalogue of M dwarfs II. High-resolution imaging with FastCam
• pyaneti II: A multidimensional Gaussian process approach to analysing spectroscopic time-series
• The CARMENES search for exoplanets around M dwarfs -- Photospheric parameters of target stars from high-resolution spectroscopy. II. Simultaneous multiwavelength range modeling of activity insensitive lines
• Diving Beneath the Sea of Stellar Activity: Chromatic Radial Velocities of the Young AU Mic Planetary System
• A Direct Imaging Survey of Spitzer detected debris disks: Occurrence of giant planets in dusty systems
• Monitoring the radio emission of Proxima Centauri
• Why is there a Dearth of Close-In Planets around Fast-Rotating stars?
• Ultra-high-time Resolution Observations of Radio Bursts on AD Leonis
• Optical and X-ray observations of stellar flares on an active M dwarf AD Leonis with Seimei Telescope, SCAT, NICER and OISTER
• Discovery of 9 New Companions to Nearby Young M Stars with the Altair AO System
• The Ca II infrared triplet's performance as an activity indicator compared to Ca II H and K
• High-resolution spectroscopy of flares and CMES on AD Leo*
• Analysis and modeling of high temporal resolution spectroscopic observations of flares on AD Leo
• The CARMENES search for exoplanets around M dwarfs. Measuring precise radial velocities in the near infrared: the example of the super-Earth CD Cet b
• 10 Years of Stellar Activity for GJ 1243
• A detailed analysis of the Gl 486 planetary system
• Mapping stellar surfaces II: An interpretable Gaussian process model for light curves
• The CARMENES search for exoplanets around M dwarfs. Mapping stellar activity indicators across the M dwarf domain
• Proxima Centauri as a Benchmark for Stellar Activity Indicators in the Near Infrared
• The CARMENES search for exoplanets around M dwarfs: Convective shift and starspot constraints from chromatic radial velocities
• Persistent starspot signals on M dwarfs: multi-wavelength Doppler observations with the Habitable-zone Planet Finder and Keck/HIRES
• A HARPS RV search for planets around young nearby stars
• The CARMENES search for exoplanets around M dwarfs: Benchmarking the impact of activity in high-precision radial velocity measurements
• Auto-correlation functions of astrophysical processes, and their relation to Gaussian processes; Application to radial velocities of different starspot configurations
• Auroral Radio Emission from Ultracool Dwarfs: a Jovian Model
• The CARMENES search for exoplanets around M dwarfs: Two Saturn-mass planets orbiting active stars
• TOI-519 b: a short-period substellar object around an M dwarf validated using multicolour photometry and phase curve analysis
• The CARMENES search for exoplanets around M dwarfs. Two terrestrial planets orbiting G 264-012 and one terrestrial planet orbiting Gl 393
• The spectral impact of magnetic activity on disk-integrated HARPS-N solar observations: exploring new activity indicators
• Activity and telluric contamination in HARPS observations of Alpha Centauri B
• The CARMENES search for exoplanets around M dwarfs. Diagnostic capabilities of strong K I lines for photosphere and chromosphere

Cited by in corpus (18)

• The CARMENES search for exoplanets around M dwarfs. Guaranteed time observations Data Release 1 (2016-2020)
• Fine structures of radio bursts from flare star AD Leo with FAST observations
• TOI-1468: A system of two transiting planets, a super-Earth and a mini-Neptune, on opposite sides of the radius valley
• Connection between planetary He I $\lambda$10830 Å absorption and extreme-ultraviolet emission of planet-host stars
• Gaussian processes for radial velocity modeling Better rotation periods and planetary parameters with the quasi-periodic kernel and constrained priors
• Revisiting Radial Velocity Measurements of the K2-18 System with the Line-by-Line Framework
• Flares, Rotation, Activity Cycles and a Magnetic Star-Planet Interaction Hypothesis for the Far Ultraviolet Emission of GJ 436
• Planetary companions orbiting the M dwarfs GJ 724 and GJ 3988. A CARMENES and IRD collaboration
• The CARMENES search for exoplanets around M dwarfs. Line-by-line sensitivity to activity in M dwarfs
• Location and energy of electrons producing the radio bursts from AD Leo observed by FAST in December 2021
• The JWST Rocky Worlds DDT Program reveals GJ 3929b to likely be a bare rock
• Radii, masses, and transit-timing variations of the three-planet system orbiting the naked-eye star TOI-396
• The CARMENES search for exoplanets around M dwarfs. The impact of rotation and magnetic fields on the radial velocity jitter in cool stars
• Starspots as the origin of ultrafast drifting radio bursts from an active M dwarf
• Multibeam SETI Observations toward Nearby M dwarfs with FAST
• The CARMENES search for exoplanets around M dwarfs : Understanding the wavelength dependence of radial velocity measurements
• Assessing the Climate and Habitability of Tidally Locked Rocky Exoplanets
• Near-IR and optical radial velocities of the active M dwarf star Gl 388 (AD Leo) with SPIRou at CFHT and SOPHIE at OHP: A 2.23 day rotation period and no evidence for a corotating planet