Testing the nonlinearity of the BVIcJHKs period-luminosity relations for the Large Magellanic Cloud Cepheids

TL;DR

This study rigorously tests the linearity of the LMC Cepheid period-luminosity relations across multiple bands, finding nonlinearity in BVIcJH but linearity in Ks and Wesenheit functions, with implications for distance measurements.

Contribution

It applies multiple statistical tests to confirm the nonlinearity of the PL relation in certain bands, clarifying previous conflicting claims.

Findings

PL relation is nonlinear in BVIcJH bands.

PL relation is linear in Ks band and Wesenheit functions.

Nonlinearity is not caused by extinction errors.

Abstract

A number of recent works have suggested that the period-luminosity (PL) relation for the Large Magellanic Cloud (LMC) Cepheids exhibits a controversial nonlinear feature with a break period at 10 days. Therefore, the aim of this Research Note is to test the linearity/nonlinearity of the PL relations for the LMC Cepheids in BVIcJHKs band, as well as in the Wesenheit functions. We show that simply comparing the long and short period slopes, together with their associate d standard deviations, leads to a strictly larger error rate than applying rigorous statistical tests such as the F-test. We applied various statistical tests to the current published LMC Cepheid data. These statistical tests include the F-test, the testimator test, and the Schwarz information criterion (SIC) method. The results from these statistical tests strongly suggest that the LMC PL relation is nonlinear in BVIcJH band but linear in the Ks band and in the Wesenheit functions. Using the properties of period-color relations at maximum light and multi-phase relations, we believe that the nonlinear PL relation is not caused by extinction errors.