  We introduce Andreev scattering (electron-hole conversion at an interface of
a normal conductor to a superconductor) at the outer vertices of a quantum star
graph and examine its effect on the spectrum. More specifically we show that
the density of states in Andreev graphs is suppressed near the Fermi energy
where a spectral gap may occur. The size and existence of such a gap depends on
one side on the Andreev scattering amplitudes and, on the other side,on the
properties of the electron-electron scattering matrix at the central vertex. We
also show that the bond length fluctuations have a minor effect on the spectrum
near the Fermi energy.
