NONPERIODIC VARIATIONS IN ASTROPHYSICAL SYSTEMS - INVESTIGATING FREQUENCY EVOLUTION

We present a method related to the wavelet transform, the Gabor transf orm, for investigating astronomical time series containing nonconstant frequencies. Instances in which such data sets may arise include vari able star light curves, numerical studies of the gravitational three-b ody problem, X-ray binaries, and signals from more exotic objects such as planets around pulsars and mass infall from accretion structures o nto compact objects. As an illustration of its power, we apply the tec hnique to a numerical data set of a gravitational three-body interacti on and to photometry of the rapidly oscillating peculiar A star HD 604 35. In the three-body example, the method provides an insightful short hand that allows for the determination of episodes where the system be haves as two nearly Keplerian orbits. For HD 60435, the power in the m ain frequency exhibits unusual evolution over the duration of the obse rvation.