Optical Gravitational Lensing Experiment Cepheids Have Lower Amplitudes in the Small Magellanic Cloud than in the Large Magellanic Cloud

Abstract

We selected Cepheids from the Optical Gravitational Lensing Experiment database for the Magellanic Clouds in the period range of 10^1.1 ≤ P ≤ 10^1.4 days. There were 33 objects in the LMC and 35 in the SMC. We find that the median amplitude of Cepheids in the LMC is 18% larger than in the SMC, a 4 σ effect. For a sample of 42 galactic Cepheids in the same period range, the median amplitude is 7% larger than in the LMC, suggesting that the higher the metal content the larger the amplitude. This implies that the period-flux amplitude relation is not universal and cannot be used to measure distances accurately, unless properly calibrated.