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The collapse of dense cores with different metallicities is studied byhydrodynamical calculations coupled with detailed chemical and radiativeprocesses. For this purpose, we construct a simple chemical network withnon-equilibrium reactions among 15 chemical species, which reproduces theabundance of important molecular coolants by more detailed network very well.The evolution is followed until the formation of a hydrostatic protostar at thecenter. In a lower-metallicity gas cloud, the temperature during the collapseremains high owing to less efficient cooling. Using the temperature evolutionat the center as a function the density, we discuss the possibility offragmentation during the dust-cooling phase. The critical metallicity for thefragmentation is 10^{-5}Z_sun assuming moderate elongation of the cloud coresat the onset of this phase. From the density and velocity distributions at thetime of protostar formation, we evaluate the mass accretion rate in thesubsequent accretion phase. Using these accretion rates, we also calculate theevolution of the protostars under the assumption of stationary accretion flow.Finally, we discuss possible suppression of fragmentation by heating of theambient gas by protostellar radiation, which is considered important in thecontemporary star formation. We argue that it is negligible for <10^{-2}Zsun.

Low-Metallicity Star Formation : Prestellar Collapse and Protostellar Accretion in the Spherical Symmetry