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The final mass of a newborn star is set at the epoch when the mass accretiononto the star is terminated. We study the evolution of accreting protostars andthe limits of accretion in low metallicity environments. Accretion rates ontoprotostars are estimated via the temperature evolution of prestellar cores withdifferent metallicities. The derived rates increase with decreasingmetallicity, from 10^-6 M_sun/yr at Z = Z_sun to 10^-3 M_sun/yr at Z = 0. Withthe derived accretion rates, the protostellar evolution is numericallycalculated. We find that, at lower metallicity, the protostar has a largerradius and reaches the zero-age main-sequence (ZAMS) at higher stellar mass.Using this protostellar evolution, we evaluate the upper stellar mass limitwhere the mass accretion is hindered by radiative feedback. We consider theeffects of radiation pressure exerted on the accreting envelope, and expansionof the HII region. The mass accretion is finally terminated by radiationpressure on dust grains in the envelope for Z > 10^-3 Z_sun and by theexpanding HII region for lower metallicty. The mass limit from these effectsincreases with decreasing metallicity from 10 M_sun at Z = Z_sun to about 300M_sun at Z = 10^-6 Z_sun. The termination of accretion occurs after the centralstar arrives at the ZAMS at all metallicities, which allows us to neglectprotostellar evolution effects in discussing the upper mass limit by stellarfeedback. The fragmentation induced by line cooling in low-metallicity cloudsyields prestellar cores with masses large enough that the final stellar mass isset by the feedback effects.

Low-Metallicity Protostars and the Maximum Stellar Mass Resulting from Radiative Feedback