The classical cepheid distance scale in the NIR bands

The Period-Luminosity (PL) relation of classical Cepheids is one of the most popular standard candle, being the first rung of the cosmic distance ladder. We discuss both theoretical and empirical features of the PL, Period-Luminosity-Color (PLC) and Period-Wesenheit (PW) relations using the largest optical (V,I; OGLEIII) and near-infrared (NIR, J,H,Ks; IRSF/SIRIUS) data sets ever collected for classical Cepheids in the Magellanic Clouds (MCs). The MCs are indeed a fundamental benchmark to calibrate the cosmic distance scale. We found that the PW relations are linear over the entire period range and show a very low dispersion. Moreover, their slopes appear independent of the metallicity since they attain similar values in the MCs and in the Galaxy. This indicates that Cepheids in NIR bands obey to universal PW relations. © Published under licence by IOP Publishing Ltd