An atomic Dicke system is coupled to a photonic band-gap continuum, wh
ich we model by a Fano-profile density of states. By introduction of t
wo pseudomodes, a Markovian master equation can be derived governing o
nly the degrees of freedom of the atoms plus the two pseudomodes. One
of the modes can be adiabatically eliminated, and effectively we then
have an atomic Dicke system coupled to a harmonic oscillator and both
systems coupled to the same flat continuum. We find that following the
superradiant regime, a metastable state is reached for the atomic sys
tem. The decay of the metastable state is nonexponential, and we deriv
e an analytical expression for the decay based on perturbation theory
and trapping states identified by the Monte Carlo wave-function method
. Further, we investigate mean-value equations of motion for the opera
tors of the system and discuss different decorrelation approximations
of the operator expectation values.