  The resonance fluorescence emitted by a system of two dipole-dipole
interacting nearby four-level atoms in J=1/2 - J=1/2 configuration is studied.
This setup is the simplest realistic model system which provides a complete
description of the (interatomic) dipole-dipole interaction for arbitrary
orientation of the interatomic distance vector, and at the same time allows for
intraatomic spontaneously generated coherences. We discuss different methods to
analyze the contribution of the various vacuum-induced coupling constants to
the total resonance fluorescence spectrum. These allow us to find a dressed
state interpretation of the contribution of the different interatomic
dipole-dipole couplings to the total spectrum. We further study the role of the
spontaneously generated coherences, and identify two different contributions to
the single-particle vacuum-induced couplings. We show that they have a
noticeable impact on the total resonance fluorescence spectrum down to small
interatomic distances, even though the dipole-dipole couplings constants then
are much larger in magnitude than the the single-particle coupling constants.
Interestingly, we find that the interatomic couplings can induce an effect of
the intraatomic spontaneously generated coherences on the observed spectra
which is not present in single-atom systems.
