Due to the unstable light curves of the asynchronous polars, their orbital periods and the spin periods of the white dwarf components are hard to be identified. WANG Qishan and his cooperators from Yunnan Observatories simulated the light curves of asynchronous and found out their periods. This work was published in The Astrophysical Journal on March 20.

A polar is a highly magnetic type of cataclysmic variables containing an accreting white dwarf and a low-mass donor star. Due to the magnetism, the white dwarf would synchronously spin, however, there are still several asynchronous polars well confirmed with their angular velocities of the white dwarfs more or less than their orbital ones.

Because of the asynchronism, the complex interaction between the magnetic field and the accretion flow makes their light curves much more unstable, which then makes the identification of their periods unsure. Wynn and King in 1991 set a model for the analysis of the periods in the light curves of the intermediate polars, which is not suitable for the analysis of the light curves from polars.

Considering the effects of the changing aspect due to the white dwarf`s spin and the variable feeding intensity caused by the asynchronism, the researchers set up a more general spot model. The spot model can produce the power spectra compatible with the observations and can be applied for the period analysis of the optical and X-ray light curve.

The simulations put up a strong criterion for identification of periods from the asynchronous polars and reveal that the long-term light curve will make the orbital signal prominent. Fitting the power distribution of the simulative light curves to that from the observational ones, researchers recognized the periods from CD Ind, BY Cam, and 1RXS J083842.1-282723.

The highest asynchronism and stable light curve help 1RXS J083842.1-282723 claim the membership of a prepolar. The new results about the period distribution of the asynchronous polars question the origin of the asynchronism in polars and new model reveals that a complex accretion geometry may cause their asynchronism.

Contact:

WANG Qishan, YNAO, CAS

wangqs@ynao.ac.cn