  Recent observations and simulations have suggested that HII regions around
massive stars may vary in their size and emitted flux on timescales short
enough to be observed. This variability can have a number of causes, ranging
from environmental causes to variability of the ionizing source itself. We
explore the latter possibility by considering the pre-main-sequence evolution
of massive protostars and conducting numerical simulations with ionizing
radiation feedback using the FLASH AMR hydrodynamics code. We investigate three
different models: a simple ZAMS model, a self-consistent one-zone model by
Offner et al. (2009), and a model fit to the tracks computed by Hosokawa &
Omukai (2009). The protostellar models show that hypercompact HII regions
around massive, isolated protostars collapse or shrink from diameters of 80 or
300 AU, depending on the model choice, down to near absence during the swelling
of stellar radius that accompanies the protostar's transition from a convective
to a radiative internal structure. This occurs on timescales as short as ~3000
years.
