  We construct a molecule of fractional vortices with fractional topological
lump charges as a baby Skyrmion with the unit topological lump charge in the
anti-ferromagnetic (or XY) baby Skyrme model, that is, an O(3) sigma model with
a four derivative term and an anti-ferromagnetic or XY-type potential term
quadratic in fields. We further construct configurations with topological lump
charges Q <= 7 and find that bound states of vortex molecules constitute
regular polygons with 2Q vertices as vortices, where the rotational symmetry
SO(2) in real space is spontaneously broken into a discrete subgroup Z_Q. We
also find metastable and arrayed bound states of fractional vortices for Q=5,6.
On the other hand, we find for Q=7 that the regular polygon is metastable and
the arrayed bound state is stable. We calculate binding energies of all
configurations.
