Spot Model for Identifications of Periods in Asynchronous Polars

Abstract

We improved the discless accretion models in Wynn & King considering the effects of the changing aspect due to the white dwarf (WD) spin and the variable feeding intensity caused by the asynchronism, and set up a more general spot model that is not sensitive to the different forms of these effects and can be applied for the period analysis of the optical and X-ray light curve. The spot model can produce the power spectra compatible with the observations, and its simulations limit the ratio P spin / P orb  < 2 between the powers at the WD spin and the binary orbital frequencies, which is a strong criterion for identification of periods. Then we recognize the periods for CD Ind, BY Cam, and 1RXS J083842.1-282723. The spot model reveals a complex accretion geometry in the asynchronous polars (APs), which may indicate that the complex magnetic field causes their asynchronism. We think 1RXS J083842.1-282723 is a prepolar because of its highest asynchronism and stable light curve. Giving the unstable accretion process in APs, the period analysis of the long-term light curve will make the orbital signal prominent.