An alternative to O - C analysis of variable star periods

Abstract

For more than a century now astronomers have used the O - C (Observed minus Calculated) method to detect the presence of systematic changes in the periods of variable stars. The method is based on an analysis of residuals from a linear fit to the observed epochs. A rather common error in applications of the method is a failure to make provision for autocorrelation which exists in the data. In this paper we consider a model that accounts for the presence of autocorrelation and develop an alternative to the O - C method of analysis. The proposed method focuses on the frequency domain characteristics of observed periods. Its use is illustrated by application to data from the variable stars X Aurigae and RY Sagittarii.