  We investigate the fast-rotating (P_orb=P_rot=0.465d), active dwarf binary
V405 And (M0V+M5V) using photometric BV(RI)_C and optical spectroscopic data.
The light variation is caused by the combined effect of spottedness and
binarity with a small eclipse. We estimate the system parameters from the
available light and radial velocity curves. Three flare events occurred during
the observations: two were found in the spectroscopic data and one was observed
photometrically in BV(RI)_C colours. An interesting eruptive phenomenon emerged
from the photometric measurements that can be interpreted as a series of
post-flare eruptions lasting for at least 3 orbits (rotations) of the system,
originating from trans-equatorial magnetic loops, which connect the active
regions in the two hemispheres. The two components of V405 And have masses well
over and below the theoretical limit of full convection. This rare property
makes the binary an ideal target for observing and testing models for stellar
dynamo action.

Solar and Stellar Astrophysics