Measuring precise radial velocities and cross-correlation function line-profile variations using a Skew Normal density

Abstract

Stellar activity is one of the primary limitations to the detection of low-mass exoplanets using the radial-velocity (RV) technique. We propose to estimate the variations in shape of the CCF by fitting a Skew Normal (SN) density which, unlike the commonly employed Normal density, includes a skewness parameter to capture the asymmetry of the CCF induced by stellar activity and the convective blueshift. The performances of the proposed method are compared to the commonly employed Normal density using both simulations and real observations, with different levels of activity and signal-to-noise ratio. When considering real observations, the correlation between the RV and the asymmetry of the CCF and between the RV and the width of the CCF are stronger when using the parameters estimated with the SN density rather than the ones obtained with the commonly employed Normal density. Using the proposed SN approach, the uncertainties estimated on the RV defined as the median of the SN are on average 10% smaller than the uncertainties calculated on the mean of the Normal. The uncertainties estimated on the asymmetry parameter of the SN are on average 15% smaller than the uncertainties measured on the Bisector Inverse Slope Span (BIS SPAN), which is the commonly used parameter to evaluate the asymmetry of the CCF. We also propose a new model to account for stellar activity when fitting a planetary signal to RV data. Based on simple simulations, we were able to demonstrate that this new model improves the planetary detection limits by 12% compared to the model commonly used to account for stellar activity. The SN density is a better model than the Normal density for characterizing the CCF since the correlations used to probe stellar activity are stronger and the uncertainties of the RV estimate and the asymmetry of the CCF are both smaller.

References in corpus (31)

• The generalised Lomb-Scargle periodogram. A new formalism for the floating-mean and Keplerian periodograms
• No planet for HD 166435
• The CORALIE survey for southern extra-solar planets VII. Two short-period Saturnian companions to HD108147 and HD168746
• Planets and Stellar Activity: Hide and Seek in the CoRoT-7 system
• A Gaussian process framework for modelling stellar activity signals in radial velocity data
• The HARPS-TERRA project I. Description of the algorithms, performance and new measurements on a few remarkable stars observed by HARPS
• State of the Field: Extreme Precision Radial Velocities
• Stellar Activity Masquerading as Planets in the Habitable Zone of the M dwarf Gliese 581
• The HARPS search for Earth-like planets in the habitable zone: I -- Very low-mass planets around HD20794, HD85512 and HD192310
• Using the Sun to estimate Earth-like planets detection capabilities II. Impact of plages
• Planetary detection limits taking into account stellar noise. I. Observational strategies to reduce stellar oscillation and granulation effects
• SOAP 2.0: A tool to estimate the photometric and radial velocity variations induced by stellar spots and plages
• Stellar activity of planetary host star HD 189733
• Search for exoplanets with the radial-velocity technique: quantitative diagnostics of stellar activity
• Measuring precise radial velocities on individual spectral lines. I. Validation of the method and application to mitigate stellar activity
• The low-level radial velocity variability in Barnard's star (=GJ 699). Secular acceleration, indications for convective redshift, and planet mass limits
• The fundamental definition of 'radial velocity'
• Doppler follow-up of OGLE transiting companions in the Galactic bulge
• Using the Sun to estimate Earth-like planets detection capabilities.I. Impact of cold spots
• Radial-Velocity Fitting Challenge. II. First results of the analysis of the data set
• Uncovering the planets and stellar activity of CoRoT-7 using only radial velocities
• Color difference makes a difference: four planet candidates around tau Ceti
• Line-profile variations in radial-velocity measurements: Two alternative indicators for planetary searches
• Using the Sun to estimate Earth-like planets detection capabilities. V. Parameterizing the impact of solar activity components on radial velocities
• Modelling the photosphere of active stars for planet detection and characterization
• SOAP-T: A tool to study the light-curve and radial velocity of a system with a transiting planet and a rotating spotted star
• Radial Velocity Fitting Challenge. I. Simulating the data set including realistic stellar radial-velocity signals
• The HARPS search for southern extra-solar planets. XLIII. A compact system of four super-Earth planets orbiting HD 215152
• The Changing Face of $\alpha$ Centauri B: Probing plage and stellar activity in K-dwarfs
• Evidence for at least three planet candidates orbiting HD20794
• Deriving stellar inclination of slow rotators using stellar activity

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• Measuring precise radial velocities on individual spectral lines : II. Dependance of stellar activity signal on line depth
• The CARMENES search for exoplanets around M dwarfs. Radial velocities and activity indicators from cross-correlation functions with weighted binary masks
• A resonant sextuplet of sub-Neptunes transiting the bright star HD 110067
• The EXPRES Stellar Signals Project II. State of the Field in Disentangling Photospheric Velocities
• The CARMENES search for exoplanets around M dwarfs. Mapping stellar activity indicators across the M dwarf domain
• Stellar activity correction using PCA decomposition of shells
• The spectral impact of magnetic activity on disk-integrated HARPS-N solar observations: exploring new activity indicators
• Long period modulation of the classical T Tauri star CI Tau: evidence for an eccentric close-in massive planet at 0.17 au
• Accounting for stellar activity signals in radial-velocity data by using Change Point Detection techniques
• TOI-1055 b: Neptunian planet characterised with HARPS, TESS, and CHEOPS
• Radii, masses, and transit-timing variations of the three-planet system orbiting the naked-eye star TOI-396
• A.C.I.D -- An Improved LSD Technique for Accurate Line Profile Retrieval
• The multi-planet system TOI-5624: Four transiting sub-Neptunes with an outer companion revealed by transit-timing variations
• Radial velocities: direct application of Pierre Connes' shift finding algorithm to Cross-Correlation Functions