NIR light-curve templates for classical Cepheids

The new approach has several advantages in sampling the light-curve of bump Cepheids when compared with the canonical phase of maximum light. We also provide new empirical estimates of the NIR-to-optical amplitude ratios for FU and FO Cepheids. We perform detailed analytical fits using seventh-order Fourier series and multi-Gaussian periodic functions.

The latter are characterized by fewer free parameters (nine vs. fifteen). The mean NIR magnitudes based on the new templates are up to 80% more accurate than single-epoch NIR measurements and up to 50% more accurate than the mean magnitudes based on previous NIR templates, with typical associated uncertainties ranging from 0.015mag (J band) to 0.019mag (K_S_ band). Moreover, we find that errors on individual distance estimates for Small Magellanic Cloud Cepheids derived from NIR PW relations are essentially reduced to the intrinsic scatter of the adopted relations.

Thus, the new templates are the ultimate tool for estimating precise Cepheid distances from NIR single-epoch observations, which can be safely adopted for future interesting applications, including deriving the 3D structure of the Magellanic Clouds.