A Comparative Study of Multiwavelength Theoretical and Observed Light
  Curves of Cepheid Variables
  We analyse the theoretical light curves of Cepheid variables at optical ({\it
UBVRI}) and near-infrared ({\it JKL}) wavelengths using the Fourier
decomposition and principal component analysis methods. The Cepheid light
curves are based on the full amplitude, nonlinear, convective hydrodynamical
models for chemical compositions representative of Cepheids in the Galaxy
($Y=0.28$, $Z=0.02$), Large Magellanic Cloud ($Y=0.25$, $Z=0.008$) and Small
Magellanic Cloud ($Y=0.25$, $Z=0.004$). We discuss the variation of light curve
parameters with different compositions and mass-luminosity levels as a function
of period and wavelength, and compare our results with observations. For a
fixed composition, the theoretical amplitude parameters decrease while the
phase parameters increase with wavelength, similar to the observed Fourier
parameters. The optical amplitude parameters obtained using canonical
mass-luminosity Cepheid models, exhibit a large offset with respect to the
observations for periods between 7-11 days, when compared to the non-canonical
mass-luminosity levels. The central minimum of the Hertzsprung progression for
amplitude parameters, shifts to the longer periods with decrease/increase in
metallicity/wavelength for both theoretical and observed light curves. The
principal components for Magellanic Clouds Cepheid models are consistent with
observations at optical wavelengths. We also observe two distinct populations
in the first principal component for optical and near-infrared wavelengths
while $J$-band contributes to both populations. Finally, we take into account
the variation in the convective efficiency by increasing the adopted mixing
length parameter from the standard 1.5 to 1.8. This results in a zero-point
offset in the bolometric mean magnitudes and in amplitude parameters (except
close to 10 days), reducing the systematically large difference in theoretical
amplitudes.
