Period-luminosity relations of type II Cepheids in the Magellanic Clouds

TL;DR

This study derives and compares period-luminosity relations of type II Cepheids in the Magellanic Clouds, revealing system-dependent slope changes and implications for distance measurements.

Contribution

It provides new PLRs for T2Cs in the SMC and compares them with LMC and globular clusters, highlighting system-dependent variations and potential metallicity effects.

Findings

SMC-LMC distance modulus difference of 0.39 mag for W Vir stars

PLR slopes vary between systems, indicating environmental effects

Period distributions of T2Cs differ across systems

Abstract

Period-luminosity relations (PLRs) of type II Cepheids (T2Cs) in the Small Magellanic Cloud are derived based on OGLE-III, IRSF/SIRIUS and other data, and these are compared with results for the Large Magellanic Cloud and Galactic globular clusters. Evidence is found for a change of the PLR slopes from system to system. Treating the longer period T2Cs (W Vir stars) separately gives an SMC-LMC modulus difference of 0.39+-0.05 mag without any metallicity corrections being applied. This agrees well with the difference in moduli based on different distance indicators, in particular the PLRs of classical Cepheids. The shorter period T2Cs (BL Her stars) give a smaller SMC-LMC difference suggesting that their absolute magnitudes might be affected either by metallicity or by age effects. It is shown that the frequency distribution of T2C periods also changes from system to system.