APPLICATION OF CUBIC-SPLINES TO THE SPECTRAL-ANALYSIS OF UNEQUALLY SPACED DATA

In the absence of a priori information, nonparametric statistical tech niques are often useful in exploring the structure of data. A least-sq uares fitting program, based on cubic B-splines has been developed to analyze the periodicity of variable star light curves. This technique takes advantage of the limited domain within which a particular B-spli ne is nonzero to substantially reduce the number of calculations neede d to generate the regression matrix. By using simple approximations ad apted to modern computer workstations, the computational speed is comp etitive with most other common methods that have been described in the literature. Since the number of arithmetic operations increases as N- 2, where N is the number of data points, this method cannot compete wi th the FFT modification of the Lomb-Scargle algorithm. However, for da ta sets with N < 10(4), it should be quite useful. Examples are shown, taken from the MACHO experiment.