星际粒子的脉冲点加热和热爆炸
Impulsive Spot Heating and Thermal Explosion of Interstellar Grains Revisited
摘要：
本文从理论上重新讨论了在寒冷、稠密的星际云中尘埃颗粒的脉冲加热问题，目的是更好地理解冰地幔爆炸解吸的主要机制。严格地表明，如果反应介质的加热发生在充分局部化的点（例如，宇宙射线对地幔的加热），那么随后的热演化就可以用一个无量纲数$λ$来表征。这个数字标识了两个不同区域之间的分歧：当$λ$超过临界值（阈值）时，热方程呈现爆炸解，即，热（化学）爆炸被触发。否则，热扩散会导致沉积的热量扩散到整个谷物上-这种情况通常称为全谷物加热。该理论使我们能够找到物理参数的临界组合，这些参数决定了由于脉冲点加热而导致的冰地幔爆炸。特别是，计算表明，重宇宙射线种类（例如，铁离子）与尘埃碰撞能够引发爆炸。根据最近计算的局部宇宙射线谱，估计了爆炸脱附的预期速率。解吸的效率，影响所有的固体物种独立于它们的结合能，被证明是与其他宇宙射线解吸机制通常认为在文献中。此外，该理论使我们能够估计可能储存在地幔中的活性物质的最大丰度，这对现有的天体化学模型提供了重要的限制。
英文摘要：
The problem of impulsive heating of dust grains in cold, dense interstellar clouds is revisited theoretically, with the aim to better understand leading mechanisms of the explosive desorption of icy mantles. It is rigorously shown that if the heating of a reactive medium occurs within a sufficiently localized spot (e.g., heating of mantles by cosmic rays), then the subsequent thermal evolution is characterized by a single dimensionless number $λ$. This number identifies a bifurcation between two distinct regimes: When $λ$ exceeds a critical value (threshold), the heat equation exhibits the explosive solution, i.e., the thermal (chemical) explosion is triggered. Otherwise, thermal diffusion causes the deposited heat to spread over the entire grain -- this regime is commonly known as the whole-grain heating. The theory allows us to find a critical combination of the physical parameters that govern the explosion of icy mantles due to impulsive spot heating. In particular, the calculations suggest that heavy cosmic ray species (e.g., iron ions) colliding with dust are able to trigger the explosion. Based on the recently calculated local cosmic-ray spectra, the expected rate of the explosive desorption is estimated. The efficiency of the desorption, which affects all solid species independent of their binding energy, is shown to be comparable with other cosmic-ray desorption mechanisms typically considered in the literature. Also, the theory allows us to estimate maximum abundances of reactive species that may be stored in the mantles, which provides important constraints on available astrochemical models.
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