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

TL;DR

This study estimates the relative distances of the Magellanic Clouds using Cepheid PW relations in NIR and optical-NIR bands, finding consistent results independent of zero-point uncertainties.

Contribution

The paper introduces a method to determine relative distances of the Magellanic Clouds using PW relations with carefully chosen pivot periods, and assesses the use of mixed-mode Cepheids as distance indicators.

Findings

Relative distance of 0.53 mag between LMC and SMC.

Pivot periods of log P=0.5 (FU) and 0.3 (FO) are optimal.

Mixed-mode Cepheids follow PW relations closely.

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 relative distances are independent of uncertainties affecting 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 found that log P=0.5 (FU) and log P=0.3 (FO) are solid choices, since they trace a main peak and a shoulder in LMC and SMC period distributions. By using the above pivot periods and ten PW relations, we found MC relative distances of 0.53$\pm$0.06 (FU) and 0.53$\pm$0.07 (FO) mag. Moreover, we investigated the possibility to use mixed-mode (FU/FO, FO/SO) Cepheids as distance indicators and we found that they follow quite well the PW relations defined by single mode MC Cepheids, with deviations typically smaller than 0.3{\sigma}.