Spot Model for Identifications of Periods in Asynchronous Polars

TL;DR

This paper introduces a generalized spot model for asynchronous polars that improves period identification by analyzing optical and X-ray light curves, revealing complex magnetic fields and accretion geometries.

Contribution

The authors develop a more general spot model that accounts for changing aspect and feeding intensity, aiding period analysis in asynchronous polars.

Findings

The model produces power spectra compatible with observations.

It limits the ratio P_spin/P_orb < 2, aiding period identification.

Identified periods for CD Ind, BY Cam, and 1RXS J083842.1-282723.

Abstract

We improved the discless accretion models of Wynn \& King, considering the effects of the changing aspect due to the white dwarf spin and the variable feeding intensity caused by the asynchronism, and set up a more general spot model which 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 white dwarf 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, which may indicate that the complex magnetic field causes their asynchronism. We think 1RXS J083842.1-282723 is a pre-polars because of its highest asynchronism and stable light curve. Giving the unstable accretion process in asynchronous polars, the period analysis of the long-term light curve will make the orbital signal prominent.