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

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.