On the relative distance of Magellanic Clouds using Cepheid NlR and Optical-NIR PW relations

Abstract. We present new estimates of the relative distance of the Magellanic Clouds(MCs) by using NIR and Optical-NIR Cepheid Period Wesenheit (PW) relations. The rela-tive distances are independent of uncertainties a ecting the zero–point of the PW relations,but do depend on the adopted pivot periods. We estimated the pivot periods for fundamental(FU) and first overtone (FO) Cepheids on the basis of their period distributions. We foundthat log P=0.5 (FU) and log P=0.3 (FO) are solid choices, since they trace a main peak anda shoulder in LMC and SMC period distributions. By using the above pivot periods and tenPW relations, we found MC relative distances of 0.53 0.06 (FU) and 0.53 0.07 (FO) mag.Moreover, we investigated the possibility to use mixed-mode (FU/FO, FO/SO) Cepheids asdistance indicators and we found that they follow quite well the PW relations defined bysingle mode MC Cepheids, with deviations typically smaller than 0.3˙. Key words. Magellanic Clouds — stars: variables: Cepheids — stars: distances — stars:oscillations