Validation of solar-cycle changes in low-degree helioseismic parameters from the Birmingham Solar-Oscillations Network

Abstract

We present a new and up-to-date analysis of the solar low-degree p-mode parameter shifts from the Birmingham Solar-Oscillations Network (BiSON) over the past 22 years, up to the end of 2014. We aim to demonstrate that they are not dominated by changes in the asymmetry of the resonant peak profiles of the modes and that the previously published results on the solar-cycle variations of mode parameters are reliable. We compare the results obtained using a conventional maximum likelihood estimation algorithm and a new one based on the Markov Chain Monte Carlo (MCMC) technique, both taking into account mode asymmetry. We assess the reliability of the solar-cycle trends seen in the data by applying the same analysis to artificially generated spectra. We find that the two methods are in good agreement. Both methods accurately reproduce the input frequency shifts in the artificial data and underestimate the amplitude and width changes by a small amount, around 10 per cent. We confirm earlier findings that the frequency and line width are positively correlated, and the mode amplitude anticorrelated, with the level of solar activity, with the energy supplied to the modes remaining essentially unchanged. For the mode asymmetry the correlation with activity is marginal, but the MCMC algorithm gives more robust results than the MLE.The magnitude of the parameter shifts is consistent with earlier work. There is no evidence that the frequency changes we see arise from changes in the asymmetry, which would need to be much larger than those observed in order to give the observed frequency shift.

Signatures of Magnetic Activity in the Seismic Data of Solar-type Stars Observed by Kepler

“…In the Sun, the amplitude of the acoustic modes is also observed to vary over the solar cycle (e.g., Elsworth et al 1993;Chaplin et al 2000;Salabert & Jiménez-Reyes 2006;Howe et al 2015), decreasing with increasing magnetic activity. Thus, the acoustic frequencies and amplitudes show an anticorrelated temporal variation over the solar cycle.…”

“…As the magnetic fields affect the medium where the acoustic waves propagate, the p-modes are sensitive to changes in the magnetic activity. In the Sun, the mode frequencies and the damping rates are observed to vary in phase with the activity level, while the mode amplitudes vary in anti-phase (e.g., Woodard & Noyes 1985;Elsworth et al 1990;Libbrecht & Woodard 1990;Chaplin et al 1998;Howe et al 2015). Although the frequency shifts are found to be well correlated with other activity indicators (e.g., 10.7 cm flux, sunspot number, sunspot area, magnetic plage strength index, photometric activity proxy) over the solar cycle (e.g., Chaplin et al 2007;Tripathy et al 2007;Jain et al 2009;Broomhall & Nakariakov 2015;Santos et al 2016Santos et al , 2017Salabert et al 2017), they also show a temporal offset (being ahead in time) in relation to those activity proxies (e.g., Jiménez-Reyes et al 1998;Moreno-Insertis & Solanki 2000;Jain et al 2009;Salabert et al 2009Salabert et al , 2015.…”

Asteroseismic constraints on active latitudes of solar-type stars: HD 173701 has active bands at higher latitudes than the Sun

“…BiSON is comprised of six ground based telescopes that observe the Sun as if it were a star in Doppler velocity. Mode frequencies were extracted from 108-day timeseries covering solar cycle 23 using the peak-bagging approach outlined in Howe et al (2015). This length of timeseries covers four solar rotations and so any signal arising from sun-spot modulation is smoothed over.…”

Revisiting the Impact of Stellar Magnetic Activity on the Detectability of Solar-Like Oscillations by Kepler

“…8,36], the amplitudes of the acoustic modes decrease with increasing activity level [e.g. 18,41,35,38]. Already observed in the Sun, such activity-related variations were first discovered in a star other than the Sun, HD 49933 observed by the CoRoT satellite, by García et al [30].…”