The formation of protostellar binaries in primordial minihaloes

The first stars are known to form in primordial gas, either in minihaloes with about 10(6) M-circle dot or so-called atomic cooling haloes of about 10(8) M-circle dot. Simulations have shown that gravitational collapse and disc formation in primordial gas yield dense stellar clusters. In this paper, we focus particularly on the formation of protostellar binary systems, and aim to quantify their properties during the early stage of their evolution. For this purpose, we combine the smoothed particle hydrodynamics code GRADSPH with the astrochemistry package KROME. The GRADSPH-KROME framework is employed to investigate the collapse of primordial clouds in the high-density regime, exploring the fragmentation process and the formation of binary systems. We observe a strong dependence of fragmentation on the strength of the turbulent Mach number M and the rotational support parameter beta. Rotating clouds show significant fragmentation, and have produced several Popualtion III proto-binary systems. We report maximum and minimum mass accretion rates of 2.31 x 10(-1) and 2.18 x 10(-4) M-circle dot yr(-1), respectively, The mass spectrum of the individual Population III proto-binary components ranges from 0.88 to 31.96 M-circle dot and has a sensitive dependence Ott the Mach number M as well as on the rotational parameter beta We also report a range from similar to 0.01 to similar to 1 for the mass ratio of our prow-binary systems.