Detection of white dwarf spin period variability in the intermediate polar V2306 Cygni

Abstract

Magnetic cataclysmic variables are close binaries which consist of a compact objecta white dwarf -and a red dwarf filling its Roche Lobe. Such systems are physical laboratories which enable study of the influence of magnetic fields on matter flows. They often exhibit spin-up or spin-down of the white dwarf, while some systems exhibit more complex behaviour of the spin period change. We monitor changes of the spin periods of white dwarfs in a sample of close binary systems to study interaction of the magnetic field and accretion processes as well as evolution of intermediate polars. Within the framework of our intermediate polar monitoring program, we obtained photometric CCD observations at several observatories. Two-period trigonometric polynomial fitting was used for determination of extrema timings. The (O-C) analysis was performed to study the variability of the orbital and spin periods of the systems. Using data taken during 9 years of observations of the magnetic cataclysmic variable V2306 Cygni (formerly known as 1WGA J1958.2+3232), we detected the spin period variability which shows a spin-up of the white dwarf with a characteristic time of (53 ± 5) • 10 4 years. The value of the spin period was 733.33976 seconds with the formal accuracy of 0.00015 seconds. We derived an improved value of the orbital period of the system to be 4.371523 ± 0.000009 hours.