Solar cycle variation of $ν_{\rm max}$ in helioseismic data and its implications for asteroseismology

The frequency, $ν_{\rm max}$, at which the envelope of pulsation power peaks for solar-like oscillators is an important quantity in asteroseismology. We measure $ν_{\rm max}$ for the Sun using 25 years of Sun-as-a-Star Doppler velocity observations with the Birmingham Solar-Oscillations Network (BiSON), by fitting a simple model to binned power spectra of the data. We also apply the fit to Sun-as-a-Star Doppler velocity data from GONG and GOLF, and photometry data from VIRGO/SPM on the ESA/NASA SOHO spacecraft. We discover a weak but nevertheless significant positive correlation of the solar $ν_{\rm max}$ with solar activity. The uncovered shift between low and high activity, of $\simeq 25\,\rm μHz$, translates to an uncertainty of 0.8 per cent in radius and 2.4 per cent in mass, based on direct use of asteroseismic scaling relations calibrated to the Sun. The mean $ν_{\rm max}$ in the different datasets is also clearly offset in frequency. Our results flag the need for caution when using $ν_{\rm max}$ in asteroseismology.

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