Sectoral r modes and periodic RV variations of Sun-like stars

Abstract

Radial velocity (RV) measurements are used to search for planets orbiting late-type main-sequence stars and confirm the transiting planets. The most advanced spectrometers are approaching a precision of $\sim 10$ cm/s that implies the need to identify and correct for all possible sources of RV oscillations intrinsic to the star down to this level and possibly beyond. The recent discovery of global-scale equatorial Rossby waves in the Sun, also called r modes, prompted us to investigate their possible signature in stellar RV measurements. R modes are toroidal modes of oscillation whose restoring force is the Coriolis force and propagate in the retrograde direction in a frame that corotates with the star. The solar r modes with azimuthal orders $3\le m\lesssim 15$ were identified unambiguously because of their dispersion relation and their long e-folding lifetimes of hundreds of days. Here we simulate the RV oscillations produced by sectoral r modes with $2\le m\le 5$ assuming a stellar rotation period of 25.54 days and a maximum amplitude of the surface velocity of each mode of 2 m/s. This amplitude is representative of the solar measurements, except for the $m=2$ mode which has not yet been observed. Sectoral r modes with azimuthal orders $m=2$ and $3$ would produce RV oscillations with amplitudes of 76.4 and 19.6 cm/s and periods of 19.16 and 10.22 days, respectively, for a star with an inclination of the rotation axis $i=60^{\circ }$. Therefore, they may produce rather sharp peaks in the Fourier spectrum of the radial velocity time series that could lead to spurious planetary detections. Sectoral r~modes may represent a source of confusion in the case of slowly rotating inactive stars that are preferential targets for RV planet search. The main limitation of the present investigation is the lack of observational constraint on the amplitude of the $m=2$ mode on the Sun.

arXiv comment7 pages; 4 figures; 1 table; accepted to Astronomy & Astrophysics

References in corpus (35)

• The generalised Lomb-Scargle periodogram. A new formalism for the floating-mean and Keplerian periodograms
• Tidal dissipation in stars and giant planets
• The HARPS-TERRA project I. Description of the algorithms, performance and new measurements on a few remarkable stars observed by HARPS
• A dynamically-packed planetary system around GJ667C with three super-Earths in its habitable zone
• Stellar Activity Masquerading as Planets in the Habitable Zone of the M dwarf Gliese 581
• 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
• Magnetic Cycles and Rotation Periods of Late Type Stars from photometric time series
• The interior rotation of a sample of gamma Doradus stars from ensemble modelling of their gravity mode period spacings
• Rotation periods of late-type dwarf stars from time-series high-resolution spectroscopy of chromospheric indicators
• Rotation, differential rotation, and gyrochronology of active Kepler stars
• The Sun as a planet-host star: Proxies from SDO images for HARPS radial-velocity variations
• The HARPS search for southern extra-solar planets XLI. A dozen planets around the M dwarfs GJ 3138, GJ 3323, GJ 273, GJ 628, and GJ 3293
• Global-scale equatorial Rossby waves as an essential component of solar internal dynamics
• Extrasolar planets and brown dwarfs around A-F type stars. I. Performances of radial velocity measurements, first analyses of variations
• Theory and evidence of global Rossby waves in upper main-sequence stars: r-mode oscillations in many Kepler stars
• The 55 Cnc system reassessed
• HARPS-N observes the Sun as a star
• The HARPS search for southern extra-solar planets XXXV. The interesting case of HD41248: stellar activity, no planets?
• Radial-Velocity Fitting Challenge. II. First results of the analysis of the data set
• Stacked Bayesian general Lomb-Scargle periodogram: Identifying stellar activity signals
• Formation and Evolution of Planetary Systems: Placing Our Solar System in Context with Spitzer
• GJ 832c: A super-earth in the habitable zone
• The main-sequence rotation-colour relation in the Coma Berenices open cluster
• The HARPS search for southern extra-solar planets. XXXIV. A planetary system around the nearby M dwarf GJ163, with a super-Earth possibly in the habitable zone
• The HADES RV Programme with HARPS-N@TNG - GJ 3998: An early M-dwarf hosting a system of Super-Earths
• Long-term radial-velocity variations of the Sun as a star: The HARPS view
• Rotation periods of exoplanet host stars
• Evidence of small-scale magnetic concentrations dragged by vortex motion of solar photospheric plasma
• Deriving the radial-velocity variations induced by stellar activity from high-precision photometry - Test on HD189733 with simultaneous MOST/SOPHIE data
• Variability of surface flows on the Sun and the implications for exoplanet detection
• Refined Properties of the HD 130322 Planetary System
• The GAPS Programme with HARPS-N at TNG XVII. Line profile indicators and kernel regression as diagnostics of radial-velocity variations due to stellar activity in solar-like stars
• The shrinking Sun: a systematic error in local correlation tracking of solar granulation

Cited by in corpus (8)

• Time-distance helioseismology of solar Rossby waves
• The EXPRES Stellar Signals Project II. State of the Field in Disentangling Photospheric Velocities
• Unsigned magnetic flux as a proxy for radial-velocity variations in Sun-like stars
• Unresolved Rossby and gravity modes in 214 A and F stars showing rotational modulation
• Tidally induced stellar oscillations: converting modelled oscillations excited by hot Jupiters into observables
• The Lowell Observatory Solar Telescope: A fiber feed into the EXtreme PREcision Spectrometer
• Rossby waves on stellar equatorial beta-planes: uniformly rotating radiative stars
• Radial Trapping of Thermal Rossby Waves within the Convection Zones of Low-Mass Stars