Fourier coefficients of variable stars. II - Light-curve analysis

In a previous paper, simple models were used to generate a set of radial velocity curves showing the effect of varying amplitude and central condensation of a star. A single parameter adequately describes the variation in the shape of all the velocity curves considered: the skewness of the curve. In this paper, light curves generated by a nonadiabatic nonlinear one-zone model are considered. A set of curves with nearly constant skewness are used to show the importance of a second parameter: the narrowness or 'acuteness' of the curve, defined in the same way as the skewness parameter. This property of the light-curve shape is responsible for the smooth variation of Fourier phases seen in RR Lyrae stars and many Cepheids. In the one-zone model, the value of the acuteness is determined by the opacity variation in the deep envelope below the ionization zones; it could prove to be a probe of interior stellar structure.