The Evolution of the First Core in Rotating Molecular Core
We present the evolution path of the first core in rotating molecular cloud core and the evolution during the second collapse phase using axisymmetric numerical calculations. The structure and evolution of the rotating first core is characterized by the angular momentum $J_{\rm core}$ and mass $M_{\rm core}$, both of which increase with time by accretion from the infalling envelope. We find the evolution path of it can be considered as a sequence of equilibrium solutions with a constant $J_{\rm core}/M_{\rm core}^2$. Such evolution paths are in good agreement with the results of three-dimensional numerical simulations. The evolution paths is completely different from spherical case. Except for extremely small rotation rate of $J_{\rm core}/M_{\rm core}^2 < 0.015 G/(\sqrt{2} c_{\rm iso})$, the first core does not increase in the central density beyond a certain maximum value and can not begins the second collapse direct and grows in mass by accretion. Such a first core has a very long time-scale and seems to suffer from a non-axisymmetric evolution. In the usual case, we expect that the time-scale of a rotating first core becomes several thousand years and several percent of the prestellar cores contain a first core at least. Such a rotating first core has a small average luminosity of $L_{\rm core} = 0.003-0.03$($\dot{M}_{\rm core}/\dot{M}_{\rm ref}$) L$_{\odot}$.