On the Variation of Fourier Parameters for Galactic and LMC Cepheids at Optical, Near-Infrared and Mid-Infrared Wavelengths

TL;DR

This study analyzes how Fourier parameters of Cepheid light curves vary across optical, near-infrared, and mid-infrared wavelengths, revealing wavelength-dependent trends and metallicity effects that inform stellar pulsation models.

Contribution

It provides a comprehensive analysis of Fourier parameter variations with period and wavelength for Galactic and LMC Cepheids, including the Hertzsprung progression, using multi-band light curve data.

Findings

Fourier amplitude parameters decrease with increasing wavelength.

Fourier phase parameters increase with increasing wavelength.

The Hertzsprung progression central period shifts with wavelength and metallicity.

Abstract

We present a light curve analysis of fundamental-mode Galactic and Large Magellanic Cloud (LMC) Cepheids based on the Fourier decomposition technique. We have compiled light curve data for Galactic and LMC Cepheids in optical ({\it VI}), near-infrared ({\it JHK}$_s$) and mid-infrared (3.6 $\&$ 4.5-$\mu$m) bands from the literature and determined the variation of their Fourier parameters as a function of period and wavelength. We observed a decrease in Fourier amplitude parameters and an increase in Fourier phase parameters with increasing wavelengths at a given period. We also found a decrease in the skewness and acuteness parameters as a function of wavelength at a fixed period. We applied a binning method to analyze the progression of the mean Fourier parameters with period and wavelength. We found that for periods longer than about 20 days, the values of the Fourier amplitude parameters increase sharply for shorter wavelengths as compared to wavelengths longer than the $J$-band. We observed the variation of the Hertzsprung progression with wavelength. The central period of the Hertzsprung progression was found to increase with wavelength in the case of the Fourier amplitude parameters and decrease with increasing wavelength in the case of phase parameters. We also observed a small variation of the central period of the progression between the Galaxy and LMC, presumably related to metallicity effects. These results will provide useful constraints for stellar pulsation codes that incorporate stellar atmosphere models to produce Cepheid light curves in various bands.