Photometric study of KR Aurigae during the high state in 2001

Abstract

We photometrically observed the VY Scl-type cataclysmic variable KR Aurigae after its final rise from a fading episode in 2000-2001. A time-resolved observation revealed that the light curve is dominated by a persistent short-term variation with time-scales of minutes to tens of minutes. On some nights, quasi-periodic variations with periods of 10-15 min were observed. No coherent variation was detected. The power spectral density of the variation has a power-law component (f-1.63). The temporal properties of the short-term variations in KR Aur present additional support for the possibility that flickering in CVs may be better understood as the result of a self-organized critical state, as in black-hole candidates. The light curve lacks "superhump"-type signals, which are relatively frequently seen in VY Scl-type systems and which are suggested to arise from a tidal instability of the accretion disk induced by changing mass-transfer rates. The present observation suggests a borderline of superhump excitation in VY Scl-type stars between mass ratios of q = 0.43 (MV Lyr) and q = 0.60 (KR Aur).