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KR Aur - extremely high variations in optical bands

ATel #10141; S. Boeva, G. Latev, Y. Nikolov, P. Nikolov, G. Nikolov, B. Spassov, B. Petrov, G. Damljanovic, M. Sekulic, R. Zamanov
on 3 Mar 2017; 05:20 UT
Credential Certification: R. K. Zamanov (rkz@astro.bas.bg)

Subjects: Optical, Binary, Cataclysmic Variable

Since 2008, the cataclysmic variable star KR Aur is in deep minimum state with a short brightening in 2010. We performed photometric monitoring in 12 nights during the period August 2016 - February 2017 with the telescopes of Rozhen (Bulgaria), Belogradchik (Bulgaria) and Vidojevica (Serbia). In the light curves obtained in August, October and November 2016 are visible variations on a time scale of e 1 hour with peak-to-peak amplitude 0.3 magnitudes, which is typical for KR Aur in low state. However on November 4, 2016 the amplitude in V band was considerably higher - 1.1 magnitude. On February 22, 2017 the variability was with amplitude 0.2 mag in V band.
On February 23, 2017 we obtained average magnitude V = 17.14 (+/- 0.02) and an amplitude of about 2.1 magnitudes in UBV bands (see Fig. 1). This is the highest amplitude in our observations of short-term variability of KR Aur. We estimate average colours U-B=-1.08 and B-V=-0.12. It seems that the mass transfer rate in the system starts to increase and probably the luminosity will rise to high state soon.