Sectoral r modes and periodic radial velocity variations of Sun-like stars

A. F. Lanza, Laurent Gizon, T. V. Zaqarashvili, Z. C. Liang, K. Rodenbeck

    Research output: Contribution to journalArticle

    Abstract

    Context. Radial velocity (RV) measurements are used to search for planets orbiting late-type main-sequence stars and to confirm the transiting planets. Aims. The most advanced spectrometers are now approaching a precision of ~10 cms -1 , which 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. These r modes are toroidal modes of oscillation whose restoring force is the Coriolis force; they propagate in the retrograde direction in a frame that co-rotates with the star. The solar r modes with azimuthal orders 3 ≤ m ≤ 15 were identified unambiguously because of their dispersion relation and their long e-folding lifetimes of hundreds of days. Methods. In this paper, we simulate the RV oscillations produced by sectoral r modes with 2 ≤ m ≤ 5 by assuming a stellar rotation period of 25:54 days and a maximum amplitude of the surface velocity of each mode of 2 ms -1 . This amplitude is representative of the solar measurements except for the m = 2 mode, which has not yet been observed on the Sun. Results. Sectoral r modes with azimuthal orders m = 2 and 3 would produce RV oscillations with amplitudes of 76:4 and 19:6 cms -1 and periods of 19:16 and 10:22 days, respectively, for a star with an inclination of the rotation axis to the line of sight i = 60°. Therefore, they may produce rather sharp peaks in the Fourier spectrum of the radial velocity time series that could lead to spurious planetary detections. Conclusions. 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 constraints on the amplitude of the m = 2 mode on the Sun.

    Original languageEnglish (US)
    Article numberA50
    JournalAstronomy and Astrophysics
    Volume623
    DOIs
    StatePublished - Mar 1 2019

    Fingerprint

    radial velocity
    sun
    stars
    oscillation
    planet
    planets
    oscillations
    velocity measurement
    equatorial wave
    Coriolis force
    Rossby wave
    stellar rotation
    main sequence stars
    confusion
    folding
    spectrometer
    planetary waves
    line of sight
    inclination
    time series

    Keywords

    • Planets and satellites: detection
    • Planets and satellites: terrestrial planets
    • Stars: late-type
    • Stars: oscillations
    • Sun: oscillations
    • Techniques: radial velocities

    ASJC Scopus subject areas

    • Astronomy and Astrophysics
    • Space and Planetary Science

    Cite this

    Lanza, A. F., Gizon, L., Zaqarashvili, T. V., Liang, Z. C., & Rodenbeck, K. (2019). Sectoral r modes and periodic radial velocity variations of Sun-like stars. Astronomy and Astrophysics, 623, [A50]. https://doi.org/10.1051/0004-6361/201834712

    Sectoral r modes and periodic radial velocity variations of Sun-like stars. / Lanza, A. F.; Gizon, Laurent; Zaqarashvili, T. V.; Liang, Z. C.; Rodenbeck, K.

    In: Astronomy and Astrophysics, Vol. 623, A50, 01.03.2019.

    Research output: Contribution to journalArticle

    Lanza, A. F. ; Gizon, Laurent ; Zaqarashvili, T. V. ; Liang, Z. C. ; Rodenbeck, K. / Sectoral r modes and periodic radial velocity variations of Sun-like stars. In: Astronomy and Astrophysics. 2019 ; Vol. 623.
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    abstract = "Context. Radial velocity (RV) measurements are used to search for planets orbiting late-type main-sequence stars and to confirm the transiting planets. Aims. The most advanced spectrometers are now approaching a precision of ~10 cms -1 , which 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. These r modes are toroidal modes of oscillation whose restoring force is the Coriolis force; they propagate in the retrograde direction in a frame that co-rotates with the star. The solar r modes with azimuthal orders 3 ≤ m ≤ 15 were identified unambiguously because of their dispersion relation and their long e-folding lifetimes of hundreds of days. Methods. In this paper, we simulate the RV oscillations produced by sectoral r modes with 2 ≤ m ≤ 5 by assuming a stellar rotation period of 25:54 days and a maximum amplitude of the surface velocity of each mode of 2 ms -1 . This amplitude is representative of the solar measurements except for the m = 2 mode, which has not yet been observed on the Sun. Results. Sectoral r modes with azimuthal orders m = 2 and 3 would produce RV oscillations with amplitudes of 76:4 and 19:6 cms -1 and periods of 19:16 and 10:22 days, respectively, for a star with an inclination of the rotation axis to the line of sight i = 60°. Therefore, they may produce rather sharp peaks in the Fourier spectrum of the radial velocity time series that could lead to spurious planetary detections. Conclusions. 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 constraints on the amplitude of the m = 2 mode on the Sun.",
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    T1 - Sectoral r modes and periodic radial velocity variations of Sun-like stars

    AU - Lanza, A. F.

    AU - Gizon, Laurent

    AU - Zaqarashvili, T. V.

    AU - Liang, Z. C.

    AU - Rodenbeck, K.

    PY - 2019/3/1

    Y1 - 2019/3/1

    N2 - Context. Radial velocity (RV) measurements are used to search for planets orbiting late-type main-sequence stars and to confirm the transiting planets. Aims. The most advanced spectrometers are now approaching a precision of ~10 cms -1 , which 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. These r modes are toroidal modes of oscillation whose restoring force is the Coriolis force; they propagate in the retrograde direction in a frame that co-rotates with the star. The solar r modes with azimuthal orders 3 ≤ m ≤ 15 were identified unambiguously because of their dispersion relation and their long e-folding lifetimes of hundreds of days. Methods. In this paper, we simulate the RV oscillations produced by sectoral r modes with 2 ≤ m ≤ 5 by assuming a stellar rotation period of 25:54 days and a maximum amplitude of the surface velocity of each mode of 2 ms -1 . This amplitude is representative of the solar measurements except for the m = 2 mode, which has not yet been observed on the Sun. Results. Sectoral r modes with azimuthal orders m = 2 and 3 would produce RV oscillations with amplitudes of 76:4 and 19:6 cms -1 and periods of 19:16 and 10:22 days, respectively, for a star with an inclination of the rotation axis to the line of sight i = 60°. Therefore, they may produce rather sharp peaks in the Fourier spectrum of the radial velocity time series that could lead to spurious planetary detections. Conclusions. 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 constraints on the amplitude of the m = 2 mode on the Sun.

    AB - Context. Radial velocity (RV) measurements are used to search for planets orbiting late-type main-sequence stars and to confirm the transiting planets. Aims. The most advanced spectrometers are now approaching a precision of ~10 cms -1 , which 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. These r modes are toroidal modes of oscillation whose restoring force is the Coriolis force; they propagate in the retrograde direction in a frame that co-rotates with the star. The solar r modes with azimuthal orders 3 ≤ m ≤ 15 were identified unambiguously because of their dispersion relation and their long e-folding lifetimes of hundreds of days. Methods. In this paper, we simulate the RV oscillations produced by sectoral r modes with 2 ≤ m ≤ 5 by assuming a stellar rotation period of 25:54 days and a maximum amplitude of the surface velocity of each mode of 2 ms -1 . This amplitude is representative of the solar measurements except for the m = 2 mode, which has not yet been observed on the Sun. Results. Sectoral r modes with azimuthal orders m = 2 and 3 would produce RV oscillations with amplitudes of 76:4 and 19:6 cms -1 and periods of 19:16 and 10:22 days, respectively, for a star with an inclination of the rotation axis to the line of sight i = 60°. Therefore, they may produce rather sharp peaks in the Fourier spectrum of the radial velocity time series that could lead to spurious planetary detections. Conclusions. 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 constraints on the amplitude of the m = 2 mode on the Sun.

    KW - Planets and satellites: detection

    KW - Planets and satellites: terrestrial planets

    KW - Stars: late-type

    KW - Stars: oscillations

    KW - Sun: oscillations

    KW - Techniques: radial velocities

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