Enhanced models for stellar Doppler noise reveal hints of a 13-year activity cycle of 55 Cancri

Abstract

We consider the impact of Doppler noise models on the statistical robustness of the exoplanetary radial-velocity fits. We show that the traditional model of the Doppler noise with an additive jitter can generate large non-linearity effects, decreasing the reliability of the fit, especially in the cases when a correleated Doppler noise is involved. We introduce a regularization of the additive noise model that can gracefully eliminate its singularities together with the associated non-linearity effects. We apply this approach to Doppler time-series data of several exoplanetary systems. It demonstrates that our new regularized noise model yields orbital fits that have either increased or at least the same statistical robustness, in comparison with the simple additive jitter. Various statistical uncertainties in the parametric estimations are often reduced, while planet detection significance is often increased. Concerning the 55 Cnc five-planet system, we show that its Doppler data contain significant correlated ("red") noise. Its correlation timescale is in the range from days to months, and its magnitude is much larger than the effect of the planetary N-body perturbations in the radial velocity (these perturbations thus appear undetectable). Characteristics of the red noise depend on the spectrograph/observatory, and also show a cyclic time variation in phase with the public Ca II H & K and photometry measurements. We interpret this modulation as a hint of the long-term activity cycle of 55 Cnc, similar to the Solar 11-year cycle. We estimate the 55 Cnc activity period by $12.6{\pm }_{1.0}^{2.5}$ yrs, with the nearest minimum presumably expected in 2014 or 2015.

arXiv comment21 pages, 12 figures, 3 tables; Accepted for publication in MNRAS; the PlanetPack2 code implementing these new Doppler noise models is available at http://sourceforge.net/projects/planetpack/

References in corpus (37)

• The generalised Lomb-Scargle periodogram. A new formalism for the floating-mean and Keplerian periodograms
• Catalog of Nearby Exoplanets
• Improving the Efficiency of Markov Chain Monte Carlo for Analyzing the Orbits of Extrasolar Planets
• Assessing statistical significance of periodogram peaks
• The Lick Planet Search: Detectability and Mass Thresholds
• Detection of a NEPTUNE-mass planet in the ${\rho }^1$ Cancri system using the Hobby-Eberly Telescope
• Radial Velocity Jitter in Stars from the California and Carnegie Planet Search at Keck Observatory
• Stellar Activity Masquerading as Planets in the Habitable Zone of the M dwarf Gliese 581
• Five Planets Orbiting 55 Cancri
• Detectability of Extrasolar Planets in Radial Velocity Surveys
• A Planet at 5 AU Around 55 Cancri
• The Twenty-Five Year Lick Planet Search
• Accounting for velocity jitter in planet search surveys
• The ELODIE survey for northern extra-solar planets III. Three planetary candidates detected with ELODIE
• H-alpha Activity of Old M Dwarfs: Stellar Cycles and Mean Activity Levels For 93 Low-Mass Stars in the Solar Neighborhood
• Radial Velocity Detection of Earth-mass Planets in the Presence of Activity Noise: The Case of Alpha Centauri Bb
• The impact of red noise in radial velocity planet searches: Only three planets orbiting GJ581?
• The HARPS search for southern extra-solar planets. XXX. Planetary systems around stars with solar-like magnetic cycles and short-term activity variation
• A Search for Multi-Planet Systems Using the Hobby-Eberly Telescope
• The 55 Cancri Planetary System: Fully Self-Consistent N-body Constraints and a Dynamical Analysis
• A Bayesian Kepler Periodogram detects a second planet in HD 208487
• Bayesian analysis of radial velocity data of GJ667C with correlated noise: evidence for only 2 planets
• A Bayesian periodogram finds evidence for three planets in HD 11964
• Orbital structure of the GJ876 extrasolar planetary system, based on the latest Keck and HARPS radial velocity data
• Revisiting rho 1 Cancri e: A New Mass Determination Of The Transiting super-Earth
• A planetary system with gas giants and super-Earths around the nearby M dwarf GJ 676A. Optimizing data analysis techniques for the detection of multi-planetary systems
• Characterizing the Orbital and Dynamical State of the HD 82943 Planetary System With Keck Radial Velocity Data
• PlanetPack: a radial-velocity time-series analysis tool facilitating exoplanets detection, characterization, and dynamical simulations
• The Impact of Stellar Oscillations on Doppler Velocity Planet Searches
• Weighted Kolmogorov-Smirnov test: Accounting for the tails
• The Lick-Carnegie Survey: Four New Exoplanet Candidates
• Up to four planets around the M dwarf GJ 163. Sensitivity of Bayesian planet detection criteria to prior choice
• Possible solution to the riddle of HD 82943 multiplanet system: the three-planet resonance 1:2:5?
• A universal approach to the calculation of the transit light curves
• The Mid-term and Long-term Solar Quasi-periodic Cycles and the Possible Relationship with Planetary Motions
• No evidence for planetary influence on solar activity
• Detecting multiple periodicities in observational data with the multifrequency periodogram - II. Frequency Decomposer, a parallelized time-series analysis algorithm

Cited by in corpus (22)

• State of the Field: Extreme Precision Radial Velocities
• The Super Earth-Cold Jupiter Relations
• The 55 Cnc system reassessed
• Color difference makes a difference: four planet candidates around tau Ceti
• Radial Velocity Data Analysis with Compressed Sensing Techniques
• Benchmarking the power of amateur observatories for TTV exoplanets detection
• A Case for an Atmosphere on Super-Earth 55 Cancri e
• Confirming Variability in the Secondary Eclipse Depth of the Super-Earth 55 Cancri e
• Homogeneously derived transit timings for 17 exoplanets and reassessed TTV trends for WASP-12 and WASP-4
• MOVES III. Simultaneous X-ray and ultraviolet observations unveiling the variable environment of the hot Jupiter HD 189733b
• Doppler Constraints on Planetary Companions to Nearby Sun-like Stars: An Archival Radial Velocity Survey of Southern Targets for Proposed NASA Direct Imaging Missions
• Catalogue of exoplanets accessible in reflected starlight to the Nancy Grace Roman Space Telescope. A population study and prospects for phase-curve measurements
• WASP-4 transit timing variation from a comprehensive set of 129 transits
• The Discovery of the Long-Period, Eccentric Planet Kepler-88 d and System Characterization with Radial Velocities and Photodynamical Analysis
• PlanetPack3: a radial-velocity and transit analysis tool for exoplanets
• The circumstellar environment of 55 Cnc: The super-Earth 55 Cnc e as a primary target for star-planet interactions
• Comparing the frequentist and Bayesian periodic signal detection: rates of statistical mistakes and sensitivity to priors
• The tidal heating of the exoplanet 55 Cnc e. The role of the orbital eccentricity
• Semi-supervised standardized detection of extrasolar planets
• Cleaning WASP-33 b transits from the host star photometric variability: analysis of TESS data from two sectors
• SPORES-HWO. II. Companion Mass Limits and Updated Planet Properties for 120 Future Exoplanet Imaging Targets from 35 yr of Precise Doppler Monitoring
• The impact of photospheric brightness field on exoplanetary transit timings and the TTV excess of HD 189733 b