The spectral properties of the quantum mechanical system consisting of a
quantum dot with a short-range attractive impurity inside the dot are
investigated in the zero-range limit. The Green function of the system is
obtained in an explicit form. In the case of a spherically symmetric quantum
dot, the dependence of the spectrum on the impurity position and the strength
of the impurity potential is analyzed in detail. It is proven that the
confinement potential of the dot can be recovered from the spectroscopy data.
The consequences of the hidden symmetry breaking by the impurity are
considered. The effect of the positional disorder is studied.