  We consider boundary conditions at the vertex of a star graph which make
Schroedinger operators on the graph self-adjoint, in particular, the
two-parameter family of such conditions invariant with respect to permutations
of graph edges. It is proved that the corresponding operators can be
approximated in the norm-resolvent sense by elements of another Schroedinger
operator family on the same graph in which the delta coupling is imposed at the
vertex and an additional point interaction is placed at each edge provided the
coupling parameters are properly chosen.
