标题： 弱宇宙射线加热事件对$\rm H_2$脱附的影响 显示英文标题

标题： The Effect of Weak Cosmic Ray Heating Events on the Desorption of $\rm H_2$

摘要： 星际冰中分子氢（${\rm H_2}$）的典型含量尚不清楚，但预计不会发生大量的${\rm H_2}$在尘埃颗粒上的冻结。 然而，化学模型普遍预测在致密云条件下会有大量$\rm H_2$的冻结，需要专门的处理来控制颗粒上的$\rm H_2$数量。 在这里，我们提出一个数值解吸模型，其中包含了由宇宙射线（CRs）引起的弱加热事件的影响，这些事件以高频率将颗粒加热到几十开尔文的温度，这改进了之前仅考虑强加热事件（颗粒最高温度接近 100 K）且发生频率较低的解吸模型。 几十开尔文的温度足以引发$\rm H_2$的有效解吸，但我们发现即使这些弱加热事件也不够频繁，无法导致显著的$\rm H_2$解吸。 考虑到弱加热事件确实会影响其他轻度结合物种的预测丰度，但这种影响仅限于低柱密度。 我们在这里做出规范假设，即颗粒是球形的，半径为0.1 $\mu$m。在颗粒尺寸分布的情况下，弱加热事件可能有助于来自小颗粒的 $\rm H_2$ 脱附，这些小颗粒数量最多。 仍需进一步研究以更好地量化宇宙射线在 $\rm H_2$ 及其他弱结合物质脱附中的作用。 显示英文摘要

摘要： The typical amount of molecular hydrogen (${\rm H_2}$) in interstellar ices is not known, but significant freeze-out of ${\rm H_2}$ on dust grains is not expected. However, chemical models ubiquitously predict large amounts of $\rm H_2$ freeze-out in dense cloud conditions, and specialized treatments are needed to control the $\rm H_2$ population on grains. Here we present a numerical desorption model where the effect of weak heating events induced by cosmic rays (CRs) that heat grains to temperatures of a few tens of Kelvin at high frequencies is included, improving upon earlier desorption models that only consider strong heating events (maximum grain temperature close to 100 K) that occur at a low frequency. A temperature of a few tens of Kelvin is high enough to induce efficient desorption of $\rm H_2$, but we find that even the weak heating events do not occur often enough to lead to significant $\rm H_2$ desorption. Taking the weak heating events into account does affect the predicted abundances of other lightly-bound species, but the effect is restricted to low column densities. We make here the canonical assumption that the grains are spherical with a radius of 0.1 $\mu$m. It is conceivable that in the case of a grain size distribution, weak heating events could provide a boost to $\rm H_2$ desorption coming off small grains, which are the most numerous. Further studies are still required to better quantify the role of CRs in the desorption of $\rm H_2$ and other weakly bound species.