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arXiv 1508.06151astro-ph.GA
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非等温Bonnor-Ebert球的稳定性。II。气体温度对稳定性的影响

On the stability of non-isothermal Bonnor-Ebert spheres. II. The effect of gas temperature on the stability

O. Sipilä, J. Harju, M. Juvela

备注：
7 pages, 5 figures; accepted for publication in A&A; abstract (heavily) abridged for arXiv
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摘要：

目的。我们研究了非等温Bonnor-Ebert球的稳定性，该模型包括气体温度的自洽计算。这样我们就可以放弃尘埃和气体温度相等的假设，并研究气体温度随气体化学演化而变化时的稳定性。方法.我们使用的气体-晶粒的化学模型，包括一个依赖于时间的处理耗尽到晶粒表面，强烈影响的气体温度作为主要的冷却剂，CO，耗尽的气体。粉尘和气体温度的解决与辐射转移。为了与以前的工作相比，我们假设的核心是深深地嵌入在一个更大的外部结构，对应于视觉消光$A_{\rm V}^{\rm ext}=10$杂志。我们发现，在这里推导出的临界无量纲半径$ξ_1$是类似于我们以前的工作，我们假设$T_{\rm dust}=T_{\rm gas}$ ; $ξ_1$值低于等温临界值$ξ_0\sim6.45$，但差异小于10%。化学演化对低质量岩心（<0.75 $M_\odot$）的稳定性条件没有显著影响。对于更高的质量，由于CO耗尽冷却的减少导致实质性的时间变化的温度和密度分布的核心。在1-2 $M_\odot$的质量范围内，$ξ_1$随着化学演变而减少，而在3 $M_\odot$以上，$ξ_1$反而增加。我们还发现，降低$A_{\rm V}^{\rm ext}$增加气体温度，特别是当气体是化学旧的，导致$ξ_1$增加相对于模型具有较高的$A_{\rm V}^{\rm ext}$。导出的$ξ_1$值接近$ξ_0$。与等温BES的恒定值$\sim$ 14.1相比，核心中心和边缘之间的密度对比度在8到16之间变化，这取决于核心质量和气体的化学年龄。

英文摘要：

Aims. We investigate the stability of non-isothermal Bonnor-Ebert spheres with a model that includes a self-consistent calculation of the gas temperature. This way we can discard the assumption of equality between the dust and gas temperatures, and study the stability as the gas temperature changes with chemical evolution of the gas. Methods. We use a gas-grain chemical model including a time-dependent treatment of depletion onto grain surfaces, which strongly influences the gas temperature as the main coolant, CO, depletes from the gas. Dust and gas temperatures are solved with radiative transfer. For comparison with previous work, we assume that the cores are deeply embedded in a larger external structure, corresponding to visual extinction $A_{\rm V}^{\rm ext}=10$ mag. Results. We find that the critical non-dimensional radius $ξ_1$ derived here is similar to our previous work where we assumed $T_{\rm dust}=T_{\rm gas}$; the $ξ_1$ values lie below the isothermal critical value $ξ_0\sim6.45$, but the difference is less than 10%. Chemical evolution does not affect notably the stability condition of low-mass cores (<0.75 $M_\odot$). For higher masses the decrease of cooling owing to CO depletion causes substantial temporal changes in the temperature and density profiles of the cores. In the mass range 1-2 $M_\odot$ , $ξ_1$ decreases with chemical evolution, whereas above 3 $M_\odot$ , $ξ_1$ instead increases. We also find that decreasing $A_{\rm V}^{\rm ext}$ increases the gas temperature especially when the gas is chemically old, causing $ξ_1$ to increase with respect to models with higher $A_{\rm V}^{\rm ext}$. The derived $ξ_1$ values are close to $ξ_0$. The density contrast between the core center and edge varies between 8 to 16 depending on core mass and the chemical age of the gas, compared to the constant value $\sim$ 14.1 for the isothermal BES.

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