2002A&A...382..152M

We present the results of a monitoring of the binary system V773 with the Effelsberg 100-m telescope extended over 522 days. A clear periodicity present in the flaring activity is confirmed by a dominant peak at 52±5 days in the Fourier power spectrum. Folding the data with the orbital period of 51.075 days the flares cluster at the periastron passage. The detailed monitoring around one periastron passage with the VLA and with the Effelsberg telescope reveals a modulation of the radio emission in agreement with the 3.4 days rotational period of the star spots, observed in the optical range. A possible scenario explains the 52 days periodicity and the 3.4 days modulation with recurrent interactions of giant loops, anchored on the two rotating stars of the system, consecutively colliding for two or three rotations during each periastron passage. Considerations about the large sizes required for the loops caused us to re-examine the generally assumed scale-height and we conclude that such a large size might be possible.