The power spectra for a set of RGB twins. The main difference between the stars is the metallicity. The position of the ℓ = 0,2 modes for the bottom spectrum is indicated by vertical lines (dash and dot-dash respectively). Modes fitted with the MCMC code (see text) are marked by symbols at the top of each spectrum and the meaning of the symbols are displayed at the bottom left corner. The power spectrum of the star in the top panel has been scaled using the ratio of the Δν’s of the two stars.