  Studies of the evolution of massive protostars and the evolution of their
host molecular cloud cores are commonly treated as separate problems. However,
interdependencies between the two can be significant. Here, we study the
simultaneous evolution of massive protostars and their host molecular cores
using a multi-dimensional radiation hydrodynamics code that incorporates the
effects of the thermal pressure and radiative acceleration feedback of the
centrally forming protostar. The evolution of the massive protostar is computed
simultaneously using the stellar evolution code STELLAR, modified to include
the effects of variable accretion. The interdependencies are studied in three
different collapse scenarios. For comparison, stellar evolutionary tracks at
constant accretion rates and the evolution of the host cores using pre-computed
stellar evolutionary tracks are computed. The resulting interdependencies of
the protostellar evolution and the evolution of the environment are extremely
diverse and depend on the order of events, in particular the time of
circumstellar accretion disk formation with respect to the onset of the
bloating phase of the star. Feedback mechanisms affect the instantaneous
accretion rate and the protostar's radius, temperature and luminosity on
timescales equal or smaller than 5 kyr, corresponding to the accretion
timescale and Kelvin-Helmholtz contraction timescale, respectively.
Nevertheless, it is possible to approximate the overall protostellar evolution
in many cases by pre-computed stellar evolutionary tracks assuming appropriate
constant average accretion rates.
