Do magnetic fields contribute to the dynamical stability of the   secondaries of CVs against mass transfer?
  We show the presence of CVs with orbital periods in the range 3.5-7 h and mass ratios q=M2/M1 above the critical values for dynamically stable mass transfer. We explore whether the magnetic fields produced in the secondaries alter the theoretical mass ratio limits allowing dynamical stability. Since magnetic fields change the specific heats and the polytropic exponent gamma of the gas in the convective envelope, the mass-radius adiabatic exponent xi_ad also changes. We find that turbulent magnetic fields can produce 10% less restrictive critical q-profiles while large-scale toroidal and poloidal fields have smaller effects. Thus, magnetic fields alone do not account for the stability of all the anomalous CVs. However, we found that the small variations of xi_ad induced by solar-type magnetic cycles explain the amplitudes of the cyclic accretion luminosity variations shown by several CVs. 
A. Bianchini (1,2), F. Tamburini (1) and P. E. Johnson (2) (1   Department of Astronomy, University of Padova, vicolo dell'O...