Observed (non model-dependent) Cepheid masses (see Evans et al. 2011, and references therein) shown together with the M − L relations of Fig. 5. Luminosities were estimated by Evans et al. (2013) or Evans et al. (2011, Polaris & FF Aql) using the period−luminosity relationship by Benedict et al. (2007). The green error bars labeled “Cep227” show the highly accurate mass estimate for OGLE-CEP-LMC-0227 (Pietrzyński et al. 2010), where the luminosity was calculated from the published radius and temperature.