Development of a new analysis technique to measure low radial-order p modes in spatially-resolved helioseismic data

Abstract

In order to take full advantage of the long time series collected by the GONG and MDI helioseismic projects, we present here an adaptation of the rotation-corrected $m$-averaged spectrum technique in order to observe low radial-order solar p modes. Modeled profiles of the solar rotation demonstrated the potential advantage of such a technique. Here we develop a new analysis procedure which finds the best estimates of the shift of each $m$ of a given ($n,\ell$) multiplet, commonly expressed as an expansion in a set of orthogonal polynomials, which yield the narrowest mode in the $m$-averaged spectrum. We apply the technique to the GONG data for modes with $1 \leq \ell \leq 25$ and show that it allows us to measure lower-frequency modes than with classic peak-fitting analysis of the individual-$m$ spectra.