EPoS Contribution |
Evolution of massive protostars growing under high accretion rates
Takashi Hosokawa National Astronomical Observatory, Tokyo, Japan | |
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. |