We discuss the two-dimensional dilaton gravity with a scalar field as the s
ource matter where the coupling with gravity is given, besides the minimal
one, trough an external field. This coupling generalizes the conformal anom
aly in the same way as those found in recent literature, but with a differe
nt motivation. The modification to the Hawking radiation is calculated expl
icitly and show an additional term that introduces a dependence on the (eff
ective) mass of the black-hole.