Measurement of low signal-to-noise-ratio solar p modes in spatially-resolved helioseismic data

TL;DR

This paper introduces a new technique for observing low signal-to-noise-ratio solar p modes, enabling measurements of modes that probe the Sun's deep interior with improved accuracy and sensitivity.

Contribution

The authors adapt a rotation-corrected, m-averaged spectrum method to detect low-frequency solar p modes in helioseismic data, surpassing classic peak-fitting analysis.

Findings

Successfully measured lower-frequency modes with the new method.

Achieved more accurate frequency and lifetime measurements of solar p modes.

Accessed modes sensitive to the solar core and radiative interior.

Abstract

We present an adaptation of the rotation-corrected, m-averaged spectrum technique designed to observe low signal-to-noise-ratio, low-frequency solar p modes. The frequency shift of each of the 2l+1 m spectra of a given (n,l) multiplet is chosen that maximizes the likelihood of the m-averaged spectrum. A high signal-to-noise ratio can result from combining individual low signal-to-noise-ratio, individual-m spectra, none of which would yield a strong enough peak to measure. We apply the technique to GONG and MDI data and show that it allows us to measure modes with lower frequencies than those obtained with classic peak-fitting analysis of the individual-m spectra. We measure their central frequencies, splittings, asymmetries, lifetimes, and amplitudes. The low-frequency, low- and intermediate-angular degrees rendered accessible by this new method correspond to modes that are sensitive to the deep solar interior down to the core and to the radiative interior. Moreover, the low-frequency modes have deeper upper turning points, and are thus less sensitive to the turbulence and magnetic fields of the outer layers, as well as uncertainties in the nature of the external boundary condition. As a result of their longer lifetimes (narrower linewidths) at the same signal-to-noise ratio the determination of the frequencies of lower-frequency modes is more accurate, and the resulting inversions should be more precise.