Time-resolved high-resolution spectroscopy of CH Cygni: evidence for a magnetic propeller state in 1994
We present high-resolution, time- and spatially resolved spectroscopic observations of CH Cyg carried out in the period 1994 May-August. A time resolution of ~10 min and S/N ratios up to 300 have been achieved. Large variations in the main peak as well as in the wings of hydrogen emission lines have been observed to evolve on time-scales from minutes to days. Discrete emission components on the red and blue sides of the main emission peak reach velocities in excess of 2000 km s^-1. Blue-shifted absorption components cluster at mean velocities -500 km s^-1 and -700 km s^-1. The presence of these high-velocity, highly variable components is explained in terms of a magnetic propeller state of the star on its way toward a new bright maximum. A low-density nebula at 1-arcsec distance from CH Cyg and aligned with the direction of the 1984 radio jet is seen in [NII], and tentatively confirmed in [OIII].