Asteroseismic Signature of a Large Active Region

Abstract

Axisymmetric magnetic activity on the Sun and Sun-like stars increases the frequencies of the modes of acoustic oscillation. However, it is unclear how a corotating patch of activity affects the oscillations, since such a perturbation is unsteady in the frame of the observer. In this paper we qualitatively describe the asteroseismic signature of a large active region in the power spectrum of the dipole and quadrupole p modes. In the corotating frame of the active region, the perturbations due to (differential) rotation and the active region completely lift the $(2\ell +1)$-fold azimuthal degeneracy of the frequency spectrum of modes with harmonic degree $\ell$. In the frame of the observer, the unsteady nature of the perturbation leads to the appearance of $(2\ell +1{)}^2$ peaks in the power spectrum of a multiplet. These peaks blend into each other to form asymmetric line profiles. In the limit of a small active region, we approximate the power spectrum of a multiplet in terms of $2\times (2\ell +1)$ peaks, whose amplitudes and frequencies depend on the latitude of the active region and the inclination angle of the star's rotation axis. In order to check the results and to explore the nonlinear regime, we also perform numerical simulations using the 3D time-domain pseudo-spectral linear pulsation code GLASS.

Accepted for publication in Frontiers in Astronomy and Space Sciences

References in corpus (13)

• The Transiting Exoplanet Survey Satellite
• ADIPLS -- the Aarhus adiabatic oscillation package
• CoRoT reveals a magnetic activity cycle in a Sun-like star
• Helioseismology of Sunspots: Confronting Observations with Three-Dimensional MHD Simulations of Wave Propagation
• Stellar magnetic activity and variability of oscillation parameters - An investigation of 24 solar-like stars observed by Kepler
• Improved pulsating models of magnetic Ap stars I: exploring different magnetic field configurations
• Generalization of the noise model for time-distance helioseismology
• Rotational splitting as a function of mode frequency for six Sun-like stars
• Shape of a slowly rotating star measured by asteroseismology
• Time-Distance Helioseismology of Two Realistic Sunspot Simulations
• Starspot rotation rates vs. activity cycle phase: Butterfly diagrams of Kepler stars are unlike the Sun's
• Helioseismic holography of simulated sunspots: magnetic and thermal contributions to travel times
• Simulating acoustic waves in spotted stars

Cited by in corpus (2)

• Detecting active latitudes of Sun-like stars using asteroseismic a-coefficients
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