标题： 低质量恒星形成嵌入阶段的寿命和包层消散率 显示英文标题

标题： Lifetime of the embedded phase of low-mass star formation and the envelope depletion rates

摘要： 受可观测的恒星形成嵌入阶段寿命分散性较大的启发，我们利用大量云核引力塌缩的数值流体力学模拟研究了上质量棕矮星和低质量恒星的 Class 0 和 Class I 阶段的持续时间。我们解析了恒星/盘/包层系统的形成，并将数值模拟扩展到晚期吸积阶段，此时包层几乎完全耗尽物质。我们采用了 Andre 等人的分类方案，并基于包层中剩余的质量计算了 Class 0 和 Class I 阶段的寿命（分别记为\tau _C0 和\tau _CI）。当考虑具有不同旋转速率、质量和大小但其他条件相同的云核时，我们的建模揭示了 Class 0 阶段的寿命与恒星质量之间存在次线性关系，最小二乘拟合指数 m = 0.8 \pm 0.05。Class I 阶段寿命与恒星质量之间的对应关系为超线性关系，指数 m = 1.2 \pm 0.05。如果考虑更广泛的云核样本，包括初始气体温度、云核截断半径、密度增强幅度、初始气体密度和角速度剖面以及磁场可能的变化，则相应的指数可能会减少多达 0.3。在大多数模型中发现 Class I 阶段的持续时间比 Class 0 阶段长，平均比值 \tau _CI / \tau _C0 \approx 1.5--2。 一个显著的例外是形成于初始密度增强较大的云核中的原恒星（YSOs），在这种情况下，\tau _C0 可能大于\tau _CI。 此外，具有冻结磁场和高旋转速率的大质量云核（≥1.0 倍太阳质量）可能具有\tau _CI /\tau _C0 的比率高达 3.0-4.0。 （摘要）。 显示英文摘要

摘要： Motivated by a considerable scatter in the observationally inferred lifetimes of the embedded phase of star formation, we study the duration of the Class 0 and Class I phases in upper-mass brown dwarfs and low-mass stars using numerical hydrodynamics simulations of the gravitational collapse of a large sample of cloud cores. We resolve the formation of a star/disk/envelope system and extend our numerical simulations to the late accretion phase when the envelope is nearly totally depleted of matter. We adopted a classification scheme of Andre et al. and calculate the lifetimes of the Class 0 and Class I phases (\tau_C0 and \tau_CI, respectively) based on the mass remaining in the envelope. When cloud cores with various rotation rates, masses, and sizes (but identical otherwise) are considered, our modeling reveals a sub-linear correlation between the Class 0 lifetimes and stellar masses in the Class 0 phase with the least-squares fit exponent m=0.8 \pm 0.05. The corresponding correlation between the Class I lifetimes and stellar masses in the Class I is super-linear with m=1.2 \pm 0.05. If a wider sample of cloud cores is considered, which includes possible variations in the initial gas temperature, cloud core truncation radii, density enhancement amplitudes, initial gas density and angular velocity profiles, and magnetic fields, then the corresponding exponents may decrease by as much as 0.3. The duration of the Class I phase is found to be longer than that of the Class~0 phase in most models, with a mean ratio \tau_CI / \tau_C0 \approx 1.5--2. A notable exception are YSOs that form from cloud cores with large initial density enhancements, in which case \tau_C0 may be greater than \tau_CI. Moreover, the upper-mass (>= 1.0 Msun) cloud cores with frozen-in magnetic fields and high cloud core rotation rates may have the \tau_CI / \tau_C0 ratios as large as 3.0--4.0. (Abdridged).