Rashed, H. Y., 1998,
Cyclotron Luminosity of Narrow offset Radiative Accretion Shocks onto Magnetic White Dwarfs,

Mu'tah Journal for research and studies, Vol. 13, No. 1, page 11.

Abstract

Optical Quasi-periodic oscillations (QPOs) are observed in some AM Her(culis) objects as broadly distributed power excesses over the frequency range 0.4 - 0.8 Hz (Middleditch 1982).  Middleditch suggested that QPOs are due to an instability of radiative shock waves discovered by Langer, Chanmugam, and Shaviv (1981) during time-dependent calculations of the accretion flows onto magnetic white dwarfs.  If this conjecture is correct, then the QPOs can be used as probes of the local conditions of the radiating plasmas and serve to place constraints on several fundamental properties of the AM Her systems (e.g. see Wood, Imamura, and Wolff 1993).

The QPOs are observed in the optical, which is thought to be due to cyclotron emission from the radiating strongly magnetic shocked plasma.  In most calculations of time-dependent radiative shocks, only bremsstrahlung is properly treated.  This work together with the calculations of the cyclotron spectra, light curves and luminosities is used to explain the important issue of the nature of the QPOs of the AM Her systems.