Idling Magnetic White Dwarf in the Synchronizing Polar BY Cam. The Noah-2 Project

TL;DR

This multi-color study of the magnetic cataclysmic variable BY Cam reveals wavelength-dependent variability, cyclotron emission signatures, and multiple periodicities, providing insights into the emission regions and accretion processes in this magnetic white dwarf system.

Contribution

The paper presents detailed multi-color photometry and analysis of BY Cam, highlighting spectral energy distribution variations and identifying multiple variability components linked to different emission regions.

Findings

Wavelength dependence of brightness variations supports cyclotron emission models.

Identification of 200-minute spin variability and QPOs at 30 and 8 minutes.

Variability amplitudes depend on wavelength and luminosity state.

Abstract

Results of a multi-color study of the variability of the magnetic cataclysmic variable BY Cam are presented. The observations were obtained at the Korean 1.8m and Ukrainian 2.6m, 1.2m and 38-cm telescopes in 2003-2005, 56 observational runs cover 189 hours. The variations of the mean brightness in different colors are correlated with a slope dR/dV=1.29(4), where the number in brackets denotes the error estimates in the last digits. For individual runs, this slope is much smaller ranging from 0.98(3) to 1.24(3), with a mean value of 1.11(1). Near the maximum, the slope becomes smaller for some nights, indicating more blue spectral energy distribution, whereas the night-to-night variability has an infrared character. For the simultaneous UBVRI photometry, the slopes increase with wavelength from dU/dR=0.23(1) to dI/dR=1.18(1). Such wavelength dependence is opposite to that observed in non-magnetic cataclysmic variables, in an agreement to the model of cyclotron emission. The principal component analysis shows two (with a third at the limit of detection) components of variablitity with different spectral energy distribution, which possibly correspond to different regions of emission. The scalegram analysis shows a highest peak corresponding to the 200-min spin variability, its quarter and to the 30-min and 8-min QPOs. The amplitudes of all these components are dependent on wavelength and luminosity state. The light curves were fitted by a statistically optimal trigonometrical polynomial (up to 4-th order) to take into account a 4-hump structure. The dependences of these parameters on the phase of the beat period and on mean brightness are discussed. The amplitude of spin variations increases with an increasing wavelength and with decreasing brightness