论文标题
晶粒尺寸分布和尺寸依赖性谷物加热对无星和前核心分子丰度的影响
Effect of grain size distribution and size-dependent grain heating on molecular abundances in starless and pre-stellar cores
论文作者
论文摘要
我们提出了一种新的气体粒化学模型，以限制晶粒尺寸分布对无星和遗前核心分子丰度的影响。我们同时引入粒度依赖性（CR）诱导的解吸效率和晶粒平衡温度。我们在一组谷物种群上保持明确的冰丰度。我们发现，依赖大小的Cr解吸效率以高度非平凡的方式影响冰的丰度，该方式取决于分子。起源于气相的物种遵循一种简单的模式，其中最小的晶粒（分布中最丰富）的冰丰度最高。在整个时间的演化过程中，有些分子（例如HCN）集中在大晶粒上，而另一些分子（例如$ \ rm n_2 $）最初集中在大谷物上，但是由于呈谷物大小的效果，在液压和氢之间依赖于晶粒尺寸的晶粒。大多数水冰是在高中密度（$ n（{\ rm H_2}）\ gtrsim 10^6 \，\ rm cm^{ - 3} $上的小谷物上，在这里，对于总水冰储层，水冰分数可以低至$ \ sim 10^{ - 3} $（$ sim 10^{ - 3} $（$ MIM）$（> 0.1）允许晶粒平衡温度随晶粒尺寸而变化，可在低密度条件下相对丰度的相对丰度变化，而星际辐射场，尤其是其紫外线分量没有减弱。我们的研究不仅意味着对无星核阶段之前的IC的初始形成，还意味着谷物种群进入原恒星阶段的相对冰丰度。特别是，如果最小的晶粒可能由于晶粒粒碰撞而损失披风，则在核心崩溃时，在原始阶段开始时的冰组成可能与爆发前阶段有很大不同。
We present a new gas-grain chemical model to constrain the effect of grain size distribution on molecular abundances in starless and pre-stellar cores. We introduce grain-size dependence simultaneously for cosmic-ray (CR)-induced desorption efficiency and for grain equilibrium temperatures. We keep explicit track of ice abundances on a set of grain populations. We find that the size-dependent CR desorption efficiency affects ice abundances in a highly non-trivial way that depends on the molecule. Species that originate in the gas phase follow a simple pattern where the ice abundance is highest on the smallest grains (the most abundant in the distribution). Some molecules, such as HCN, are instead concentrated on large grains throughout the time evolution, while others (like $\rm N_2$) are initially concentrated on large grains, but at late times on small grains, due to grain-size-dependent competition between desorption and hydrogenation. Most of the water ice is on small grains at high medium density ($n({\rm H_2}) \gtrsim 10^6 \, \rm cm^{-3}$), where the water ice fraction, with respect to total water ice reservoir, can be as low as $\sim 10^{-3}$ on large (> 0.1 $μ$m) grains. Allowing the grain equilibrium temperature to vary with grain size induces strong variations in relative ice abundances in low-density conditions where the interstellar radiation field and in particular its ultraviolet component are not attenuated. Our study implies consequences not only for the initial formation of ices preceding the starless core stage, but also for the relative ice abundances on the grain populations going into the protostellar stage. In particular, if the smallest grains can lose their mantles due to grain-grain collisions as the core is collapsing, the ice composition in the beginning of the protostellar stage could be very different to that in the pre-collapse phase.
