Low-frequency, low-degree solar p-mode properties from 22 years of Birmingham Solar Oscillations Network data

The solar low-degree low-frequency modes of oscillation are of particular interest as their frequencies can be measured with very high precision and hence provide good constraints on seismic models. Here we detect and characterize these valuable measures of the solar interior from a 22 yr Birmingham Solar Oscillations Network data set. We report mode frequencies, line widths, heights, amplitudes, and rotational splitting, all with robust uncertainties. The new values of frequency, rotational splitting, amplitude, and line width we provide will help place new constraints on hydrostatic and rotational structure, plus diagnostics of near-surface convection. Further to this, by assuming simple power laws, we extrapolate mode properties to lower frequencies. We demonstrate that the low-l low-frequency p modes have a low signal-to-noise ratio and that this cannot be overcome simply by continued observation. It will be necessary to observe the Sun in novel ways to ‘beat’ the intrinsic granulation noise.