  We calculate the evolution of cloud cores embedded in different envelopes to
investigate environmental effects on the mass accretion rate onto protostars.
As the initial state, we neglect the magnetic field and cloud rotation, and
adopt star-forming cores composed of two parts: a centrally condensed core and
an outer envelope. The inner core has a critical Bonnor-Ebert density profile
and is enclosed by the outer envelope. We prepare 15 star-forming cores with
different outer envelope densities and gravitational radii, within which the
gas flows into the collapsing core, and calculate their evolution until $\sim 2
\times10^5$ yr after protostar formation. The mass accretion rate decreases as
the core is depleted when the outer envelope density is low. In contrast, the
mass accretion rate is temporarily enhanced when the outer envelope density is
high and the resultant protostellar mass exceeds the initial mass of the
centrally condensed core. Some recent observations indicate that the mass of
prestellar cores is too small to reproduce the stellar mass distribution. Our
simulations show that the mass inflow from outside the core contributes greatly
to protostellar mass growth when the core is embedded in a high-density
envelope, which could explain the recent observations.
