uvby - β photoelectric photometry of Cepheid stars
We present time-series uvby − β photometry of 41 classical Cepheid stars. A brief discussion of a comparison between the present data and previous photometric observations is included.
A method of solving the eikonal equation, in either flat or curved space–times, with arbitrary Cauchy data, is extended to the case of data given on a characteristic surface. We find a beautiful relationship between the Cauchy and characteristic data for the same solution, namely they are related by a Legendre transformation. From the resulting solutions, we study and describe the wave-front singularities that are associated with their level surfaces (the characteristic surfaces or “big wave fronts”).