Nonradial pulsations of the hot component of the symbiotic star CH Cyg during its active phase

Abstract

We observed the symbiotic star CH Cyg with the 70 cm telescope of the Crimean Astrophysical Observatory in 1982, during its active phase, when it was brighter than 6^m in the V band. We simultaneously detected the continuum brightness at wavelengths of 3737, 5092, and 5500 Å with a time resolution of 20 s. We present light curves for these wavelengths for four nights between July 13 and August 22, demonstrating the character of the star’s rapid variations. Various frequency-analysis methods were applied to the data series at 3737 and 5092 Å, where the light from the hot component made an appreciable contribution. For both series, we find some 20 similar frequencies corresponding to periods ranging from 150 to 6000 s. Our estimates of the significance of the identified frequencies indicate that the significance level exceeds 3 σ in all cases, and is even higher in most cases. For many of the oscillations, the amplitudes varied on time scales shorter than one day. Multiperiodicity and variable oscillation amplitudes are characteristic of nonradial pulsations. We conclude that nonradial oscillations typical of a white dwarf’s g modes were excited during the symbiotic star’s state of highest activity.