The Evolution of the First Core in Rotating Molecular Core

The standard star formation scenario is based on spherically symmetric radiative hydrodynamics calculations. In this paper, we focus on the evolution of the rotating non-spherical cloud through the first core and second collapse phases 10 < ρ < 10 3 g cm using axisymmetric numerical calculations. The rotating first core evolves under the influence of mass and angular momentum accretion from the infalling envelope. The structure of the rotating first core is characterized by the angular momentum Jcore and massMcore, both of which increase with time J̇core, Ṁcore > 0. The evolution path of a rotating first core is considered as a sequence of equilibrium solutions with a constant Jcore/M 2 core. Such evolution paths are in good agreement with the results of three-dimensional numerical simulations. Only the slowly rotating first core with Jcore/M 2 core < 0.015G/( √ 2ciso) begins the second collapse directly. On the other hand, the cloud with a rotation rate of Jcore/M 2 core > 0.015G/( √ 2ciso) does not increase in the central density beyond a certain maximum value. Although the first core grows in mass by accretion, this first core does not begin the second collapse directly. Such a first core has a very long time-scale and seems to suffer from a non-axisymmetric evolution, such as formation of massive spiral arms, deformation into a bar, or fragmentation. In the usual case, the time-scale of a rotating first core becomes several thousand years or more. So we expect that at least several percent of the prestellar cores contain a first core. The rotating first core has a small average luminosity of Lcore = 0.003− 0.03(Ṁcore/Ṁref) L⊙. However, we expect that the rotating first core repeats temporal increases in the luminosity during its first core phase. Subject headings: theory — hydrodynamics — methods: numerical — accretion disks — stars: formation e-mail: [email protected] School of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI); e-mail [email protected]