The peculiar light curve of the Symbiotic Star AX Per of the last 125 years

Abstract

We analyze the last 125 years optical light curve of the symbiotic star AX Per through some remarkable correlations that we discovered in its power spectrum. The data were assembled from the literature and from the AAVSO database. A series of 6 major outbursts dominate the light curve. They are presented in the power spectrum as 13 harmonics of the fundamental frequency fa=1/Pa=1/23172 day-1. We refer to them as the "red" frequencies. Oscillations with the binary periodicity of the system Pb=1/fb=681.48 d are also seen in the light curve, with particularly large amplitudes during outbursts. The fb peak in the power spectrum is accompanied by 13 other peaks on each side, to which we refer as the "blue" frequencies. A distinct structure in the frequency distribution of the blue peaks, as well as in their peak power are best interpreted as reflecting beating of the 13 "red" frequencies with the binary one. We suggest, following others, that the major outbursts of the system result from events of intense mass loss from the giant star. Mass accretion onto the hot component, partially through the L1 point of the system, took place in the last 125 years at a rate that oscillated with the 13 first harmonics of the fa frequency. The binary orbit is slightly eccentric and periastron passages induced modulation of the L1 accretion at the binary frequency. Hence the fb oscillations in the brightness of the star of amplitude that is modulated by the "red" frequencies of the system.