We present multiepoch Very Large Array (VLA) observations at 1.4 GHz, 4.9
GHz, 8.5 GHz and 14.9 GHz for a sample of eight RS CVn binary systems. Circular
polarization measurements of these systems are also reported. Most of the
fluxes observed are consistent with incoherent emission from mildly
relativistic electrons. Several systems show an increase of the degree of
circular polarization with increasing frequency in the optically thin regime,
in conflict with predictions by gyrosynchrotron models. We observed a reversal
in the sense of circular polarization with increasing frequency in three
non-eclipsing systems: EI Eri, DM Uma and HD 8358. We find clear evidence for
coherent plasma emission at 1.4 GHz in the quiescent spectrum of HD 8358 during
the helicity reversal. The degrees of polarization of the other two systems
could also be accounted for by a coherent emission process. The observations of
ER Vul revealed two U-shaped flux spectra at the highest frequencies. The
U-shape of the spectra may be accounted for by an optically thin
gyrosynchrotron source for the low frequency part whereas the high frequency
part is dominated by a thermal emission component.Comment: 12 pages, 8 figures, LaTeX, uses aa.cls. Accepted for publication in
A&
