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Published online by Cambridge University Press: 07 August 2017
M31 and M33 are the two nearest extragalactic spirals. They are therefore particularly suitable for studies of stellar populations. From integrated photometry spiral galaxies are known to consist of four components: (1) a nucleus, (2) a nuclear bulge, (3) an (exponential) disk and (4) a halo. These stellar components are embedded within a massive invisible halo.