EDP Sciences
Free access
Volume 403, Number 2, May IV 2003
Page(s) 613 - 624
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20030361

A&A 403, 613-624 (2003)
DOI: 10.1051/0004-6361:20030361

VLA multifrequency observations of RS CVn binaries

J. García-Sánchez, J. M. Paredes and M. Ribó

Departament d'Astronomia i Meteorologia, Universitat de Barcelona, Av. Diagonal 647, 08028 Barcelona, Spain
    e-mail: josep@am.ub.es;mribo@am.ub.es
(Received 15 November 2002 / Accepted 28 February 2003)

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.

Key words: radio continuum: stars -- stars: binaries: general -- stars: binaries: eclipsing -- polarization

Offprint request: J. García-Sánchez, jgarcia@am.ub.es

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