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High accretion rates of more than 10-4 Msun/yr
are envisaged in some current scenarios of massive star
formation. Detailed modeling of such protostars is still
limited, but needed for future high-resolution simulations and
observations probing massive star formation.
We study evolution of massive protostars
growing uder such high accretion rates by numerically
solving the detailed inner structure of the protostar.
Very wide range of accretion rates from 10-6 M_sun/yr to
more than 10-3 Msun/yr are adopted in our calculations.
Evolution under the high accretion rates is fairly different
from that of lower-mass protostars,
for which a lower accretion rate, 10-5 M_sun/yr is presumed.
The stellar radius is very large and exceeds 100 Rsun.
Deuterium burning hardly affects the evolution, and
the protostar remains radiative even after its ignition.
It is not until the protostar has grown massive enough that
hydrogen burning begins and the protostar reaches the ZAMS.
We also find that growth of the protostar by steady accretion
terminates before reaching the ZAMS under the very high accretion
rates, when total luminosity of the protostar approaches
about half of the Eddington luminosity. Therefore, there should
be an upper mass limit of pre-main-sequence stars at about 60 Msun.
We also propose that the protostar enshrouded in Orion KL/BN
nebula is a strong candidate of such protostars growing under
the high accretion rate.
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