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\label{logLlogMz}Astronomy&AstrophysicsReview Close-up of the 1–2.5 \(M_{\odot}\) range of the mass-luminosity relation in Fig. \ref{logLlogM}. The very significant scatter in \(\log L\) at each mass value is due to the combined effects of stellar evolution and abundance differences (see text). Open circles: stars classified as giants.