A SEARCH FOR RAPID RADIO FLUX VARIATIONS IN 2 RS-CVN BINARY-SYSTEMS

A Very Large Array search for rapid changes in the radio flux densitie s of two RS Canum Venaticorum type stars, UX Ari and BH CVn is describ ed. As is well known, this group of binary stars exhibits intense acti vity in the x-ray, radio, visible, and ultraviolet domains and this ac tivity manifests itself as flare-like events. Radio continuum measurem ents were performed in a search for radio intensity variations with ti me scales of minutes to seconds. The earlier results that these stars are sources of relatively strong, circularly polarized radio emission variable on a time scale of hours, were confirmed but rapid variations with amplitudes larger than our measurement error were not found. The upper limits for any periodic signals in UX Ari and BH CVn are, respe ctively, 0.018 and 0.015 mJy. The aperiodic variability was dominated by the low frequency nu-1 ''flicker'' noise. Analysis of the scatter i n the data gave 1-2 mJy as a typical value of the random fluctuation i n the signal for an integration time of 3.3 s, which is fully consiste nt with instrumental system noise. A stepwise increase in the flux of BH CVn observed in the middle of our observations indicates that it wa s caused either by a localized region of high brightness temperature w hich most probably emerged from behind the stellar limb or by a flat-t opped flare of unusual steadiness.