Optimal curve fitting procedures applied to the light curves of classical cepheids

Optimal curve fitting procedures based on the well known Baade/Wesselink methodology have been applied to Stebbinset al.'s 6-colour photometry of the classical cepheids Cep and Aql. Radial velocity data have been represented by a Fourier series, while the brightness temperature at the effective wavelength of observation forms a convenient temperature variable in the fitting function. This fitting function requires the specification of six parameters which thus play the role of unknowns in the optimization problem, though, in fact, all six parameters cannot be independently determined.The formulation involves a simple connection between colours and brightness temperatures, and model stellar atmosphere calculations can provide such a connection. The model stellar atmosphere data of Carbon and Gingerich (1969), which take careful account of line blanketing effects are, to some extent, supported by the results for Aql, though the position is less certain in the case of Cep. On the basis of the Carbon and Gingerich data, and if we take into account various estimates of the interstellar reddening, the absolute magnitudes of Cep and Aql areM _v=–3.57 andM _v=–3.79, respectively; but optimal curve fits would decrease both these values by about 0^m.09.