Statistical Tests for Changing Periods in Sparsely Sampled Data

Abstract

The rate of change of physical periods in stars and stellar systems is arguably the most important diagnostic of the physical processes driving the evolution of those systems. For periods measured from a fiducial phase marker (eclipse, maximum brightness, etc.), the period derivative is measured by fitting a non-linear ephemeris to the fiducial phase timings. This method assumes that the uncertainties in the residuals are uncorrelated measurement errors. Variations in the residuals which mimic period change can be caused by intrinsic or correlated variability in the fiducial timing mark. We have developed statistical tests which can distinguish between these two cases and applied these tests to orbital period measurements of low mass X-ray binaries which have been reported to have orbital period evolution.