  We study quantum correlations in a bipartite heteronuclear $(N-1)\times1$
system in an external magnetic field. The system consists of a spin ring with
an arbitrary number $N-1$ of spins on the ring and one spin in its center. The
spins on the ring are connected by secular dipole-dipole interactions and
interact with the central spin through the Heisenberg $zz$-interaction. We show
that the quantum discord, describing quantum correlations between the ring and
the central spin, can be obtained analytically for this model in the high
temperature approximation. The model allows us to find contributions of
different parts of the spin-spin interactions to quantum correlations. We also
investigate the evolution of quantum and classical correlations at different
numbers of spins.
