We present the results of numerically solving the rate equations for the first 31 rotational states of CS in the ground vibrational state to determine the conditions under which the J=1-0, J=2-1 and J=3-2 transitions are inverted to produce maser emission. The essence of our results is that the CS($v=0$) masers are collisionally pumped and that, depending on the spectral energy distribution, dust emission can suppress the masers. Apart from the J=1-0 and J=2-1 masers the calculations also show that the J=3-2 transition can be inverted to produce maser emission. It is found that beaming is necessary to explain the observed brightness temperatures of the recently discovered CS masers in W51 e2e. The model calculations suggest that a CS abundance of a few times $10^{-5}$ and CS($v=0$) column densities of the order $10^{16}\,\mathrm{cm^{-2}}$ are required for these masers. The rarity of the CS masers in high mass star forming regions might be the result of a required high CS abundance as well as due to attenuation of the maser emission inside as well as outside of the hot core.

中文翻译：

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关于 W51 e2e 中 CS(v=0) 脉泽的泵浦

我们给出了对地面振动状态下 CS 的前 31 个旋转状态的速率方程进行数值求解的结果，以确定 J=1-0、J=2-1 和 J=3-2 跃迁反转的条件产生脉泽发射。我们结果的本质是 CS($v=0$) 脉泽受到碰撞泵浦，并且根据光谱能量分布，尘埃发射可以抑制脉泽。除了 J=1-0 和 J=2-1 脉泽之外，计算还表明 J=3-2 跃迁可以反转以产生脉泽发射。发现光束对于解释最近在 W51 e2e 中发现的 CS 脉泽观测到的亮度温度是必要的。模型计算表明，CS 丰度是 $10^{-5}$ 的几倍，CS($v=0$) 列密度为 $10^{16}\，\mathrm{cm^{-2}}$ 是这些脉泽所必需的。CS 脉泽在高质量恒星形成区的稀有性可能是由于所需的高 CS 丰度以及热核内部和外部的脉泽发射衰减所致。