Solar cycle variation of νmax in helioseismic data and its implications for asteroseismology

The frequency, ν_max, at which the envelope of pulsation power peaks for solar-like oscillators is an important quantity in asteroseismology. We measure ν_max for the Sun using 25 yr 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 Global Oscillation Network Group and Global Oscillations at Low Frequency, 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_max with solar activity. The uncovered shift between low and high activity, of ∼eq 25 μ Hz, 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_max in the different data sets is also clearly offset in frequency. Our results flag the need for caution when using ν_max in asteroseismology.