MONITORING MWC 560-V694 MONOCEROTIS IN 1990-1995 .1. CONVENTIONAL ANDHIGH-SPEED UBV PHOTOMETRY

We present results of an extensive photometric monitoring campaign of the peculiar emission star MWC 560 that covers the range 1990-1995. Th e time interval corresponds to the length of the proposed orbital peri od of this highly peculiar binary, which attracted considerable intere st in January-April 1990, when absorption components, shifted by -6000 km s(-1) from corresponding emission lines, were observed. Here we pr esent photometric data secured during: 113 nights of conventional UBV photoelectric photometry, 45 nights of high speed UBV photoelectric ph otometry to study the flickering activity, and 682 visual photometric estimates. MWC 560 has experienced a decrease in magnitude since the b right (V=9.(m)2) phase in 1990. After the minimum reached in May 1994 (V=10.(m)7), the star is currently increasing slowly in brightness. Th e decrease has been accompanied in all bands by large fluctuations sup erimposed on the mean trend. The B - V colour has shown a steady incre ase by 0.(m)033 yr(-1). U - B has remained stable at -0.(m)07 since la te 1990. In all the observing nights devoted to high speed photometry we observed flickering activity in MWC 560. The data show that the fli ckering amplitude Delta U increases with the decrease of the U magnitu de. Quasi-periodic variations have always been detected. A period of s imilar to 70 min has been observed in similar to 13 nights which is cl ose to the similar to 60 min quasi-period reported by Michalitsianos e t al. (1993). However, no coherent variability is traceable throughout the whole set of flickering data.*