What Determines the Typical Mass of Dense Cores in Quiescent, Nonmagnetized Molecular Clouds?

By means of one-dimensional simulations, we study the collapse of a quiescent, nonmagnetized lamentary molecular cloud, taking into account the heating and cooling processes. At the initial state, the model cloud has the central density of 10 3 cm ?3 and temperature of 15 K. We follow its contraction until the central density reaches to 10 10 cm ?3. The cloud contracts mainly due to the CO line cooling and cooling by gas-dust interaction. During the contraction, the cloud temperature stays nearly constant at 10 K. When the central density exceeds 10 4?5 cm ?3 , a shock wave is formed at r 0:05 pc. The shock wave separates the cloud into two parts, i.e., a dense spindle and a diiuse envelope. Applying linear theory, we nd that the collapsing spindle is likely to fragment into dense cores by the stage that the central density reaches to n c 10 8?9 cm ?3 , if the amplitude of the perturbation is greater than A > 10 ?2. The masses of the dense cores depend on the initial amplitude of the perturbation. When the initial amplitude of the perturbation is small (A < 10 ?1), the spindle fragments into cores with mass of 0:1 ? 0:5M. On the other hand, when the spindle has relatively large inhomogenity (A 10 ?1), it fragments into cores with mass of 10M .