2002A&A...391..617I

Spectral variations of the peculiar symbiotic object MWC 560 (V694 Mon) have been monitored for 10 years since 1991. The radial velocity of the blue edge of the broad absorption components of H I lines is measured to evaluate the outflow velocity of the jet. The variation of the outflow velocity suggests that there are active and stable stages in this system. The outflow velocity in the stable stage seems to vary according to the long-term light variation with a period of 1930 days. This variation of the outflow velocity could be explained with a model of gas outflow from an accretion disk precessing with a period of 1930 days. If the observed amplitude of the light variation, Δm_pg≃0.72mag, was purely due to the precession, the maximum inclination of the disk to the line of sight should be about 59 degrees. Since the outflow is observed always as absorption, the open angle of the outflow should be larger than 59 degrees. However, the amplitude of the light variation due to the precession of the disk seems to be still rather uncertain. In the active stage the outflow velocity was much higher (in the negative sense) than in the stable stage, and rapid variations of the outflow velocity were observed. During the outburst in 1990, this object was in the active stage, while no significant brightening was observed in the active stages in 1993 and 1999 at least in the V band. The durations of the active stages were several months.