Orbital and spin variability of the intermediate polar BG CMi

¹ University Observatory, Chungbuk National University, 361-763 Cheongju, Korea
² Institute for Basic Science Research, Chungbuk National University, 361 763, Korea
³ Department of Astronomy, Odessa National University, T.G. Shevchenko Park, 65014 Odessa, Ukraine e-mail: il-a@mail.ru
⁴ Crimean Astrophysical Observatory, 98409 Nauchny, Ukraine
⁵ Korea Astronomy Observatory and Space Science Institute, Daejeon 305-348, Korea

Received: 4 March 2005
Accepted: 10 June 2005

Abstract

Results of a CCD study of the variability of the cataclysmic variable BG CMi obtained at the Korean 1.8 m telescope in 2002–2005 are presented. The “multi-comparison star” method had been applied for better accuracy estimates. The linear ephemeris based on 19 mean maxima for 2002–2005 is HJD The period differs from that predicted by the quadratic ephemeris by Pych et al. (1996, AcA, 46, 279) leading to a possible cycle miscount. The statistically optimal ephemeris is a fourth-order polynomial, as a quadratic or even a cubic ephemeris leads to unaceptably large residuals: Min.HJD =  Thus the rate of the spin-up of the white dwarf is decreasing. An alternative explanation is that the spin-up has been stopped during recent years. The deviations between the amplitudes of the spin variability in V and R, as well as between phases are not statistically significant. However, the orbital light curves exhibit distinct difference; the corresponding color index shows a nearly sinusoidal shape with a maximum at orbital phase ~0.2. The variations of the amplitude of spin waves shows a short maximum at the phase of the orbital dip. The corrected ephemeris for orbital minima is Min.HJD =  with a narrow dip occuring 0.07P later. The rate of the spin period variation seems to be changed, justifying the necessity of regular observations of intermediate polars.