Determining low- ℓ p-mode frequency shifts in Sun-like stars

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Abstract
Context. Acoustic mode frequencies in the Sun and Sun-like stars change due to magnetic activity on timescales that are much longer than that of the star’s rotation and much shorter than that of its evolution. Given the poor S/N of the observed stellar p-modes, it is challenging to measure the changes of individual mode frequencies. Typically, power spectra of different time series segments are cross-correlated to estimate a mean p-mode frequency change, which ends up being an average of the individual mode contributions. Aims. We seek to enhance the cross-correlation method by introducing a novel and computationally cheap method that enables us to disentangle p-mode frequency changes for different spherical harmonic degrees, ℓ . Methods. We designed filters that, if the inclination angle and rotation rate are already measured, enable the isolation of δω ℓ and frequency changes of modes with a given ℓ while preventing bias creeping in from neighbouring modes. We performed Monte Carlo simulations to quantify the uncertainty in the estimation of δω ℓ . Results. We validated our method against well-studied solar data (from SOHO/VIRGO and BiSON) and demonstrate its applicability to the solar-like Kepler star KIC 8006161.
Funding Information
  • Deutsche Forschungsgemeinschaft (530101854)
  • Science and Technology Facilities Council (ST/V000500/1)

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