2014MNRAS.443.2444K

We report the results of photometry of the intermediate polar V647 Aur. Observations were obtained over 42 nights in 2012 and 2013. The total duration of the observations was 246h. We clearly detected three oscillations with periods of 932.9123±0.0011, 1008.30797±0.00038 and 1096.955±0.004 s, which may be the white dwarf spin period and two orbital sidebands, respectively. The oscillation with a period of 932.9123 s has a quasi-sinusoidal pulse profile with a slightly changeable semi-amplitude from 10.9 mmag in 2012 to 12.5 mmag in 2013. The oscillation with a period of 1008.307 97 s has a slightly asymmetric pulse profile with a remarkable small hump on the ascending part. The semi-amplitude of this oscillation is highly changeable both in a time-scale of days (26-77 mmag) and in a time-scale of years (47 mmag in 2012 and 34 mmag in 2013). The oscillation with a period of 1096.955 s has a highly asymmetric pulse profile with a semi-amplitude of about 6 mmag. The three detected oscillations imply an orbital period of 3.46565±0.00006h. By comparing our data with the data of Gänsicke et al., which were obtained eight years ago, we discovered that the spin period of the white dwarf in V647 Aur decreases with dP/dt = (-1.36±0.08)x10^–10. This important result should be confirmed by future observations. Our oscillation ephemerides and times of maxima can be useful for this confirmation.