Adventures of a tidally induced bar
  Using N-body simulations, we study the properties of a bar induced in a dwarf
galaxy as a result of tidal interaction with the Milky Way. The dwarf is
initially composed of a disk embedded in a dark matter halo and we follow its
evolution on a typical orbit for 10 Gyr. It undergoes an evolution typical of
tidally stirred dwarf galaxies: it loses mass, the stellar component transforms
from a disk to a spheroid and the rotation of the stars is partially replaced
by random motions. A tidally induced bar forms at the first pericentre passage
and survives until the end of the evolution. Fourier decomposition of the
distribution of stars reveals that only even modes are significant and preserve
a hierarchy so that the bar mode is always the strongest. They show a
characteristic profile with a maximum, similar to simulated bars forming in
isolated galaxies and observed bars in real galaxies. We adopt the maximum of
the bar mode as a measure of the bar strength and we estimate the bar length by
comparing the density profiles along the bar and perpendicular to it. Both the
bar strength and the bar length decrease with time, mainly at pericentres, as a
result of tidal torques acting at those times and not to secular evolution. The
pattern speed of the bar varies significantly on a time scale of 1 Gyr and
seems to be fully controlled by the orientation of the tidal torque from the
Milky Way. The bar is never tidally locked but we discover a hint of a 5/2
orbital resonance between the third and fourth pericentre passage. The speed of
the bar expressed in terms of the ratio of the bar length to the corotation
radius decreases in the long run so that the bar changes from initially rather
fast to slow in the later stages. The boxy/peanut shape is clearly visible in
the edge-on view between the second and third pericentre and its occurrence is
preceded by a short period of buckling instability.
