Complete depletion in prestellar cores
Complete depletion in prestellar cores
复制标题
前恒星核心完全耗尽
DOI：
10.1051/0004-6361:20035718
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发表时间：
2004
影响因子：
6.5
通讯作者：
G. P. Forêts
中科院分区：
文献类型：
--
作者：
C. Walmsley;D. Flower;G. P. Forêts
我们针对完全耗尽的低质量前原恒星核心的条件进行了电离平衡和氘分馏的计算，其中C、N和O等重元素已经从气相中消失，并被纳入冻结在尘埃颗粒表面的冰幔中。我们特别强调对 H 2 D + 朝向前星核心 L 1544 中心的最新观测结果的解释（Caselli 等人 [CITE]），并计算双极扩散时标。我们明确考虑 H 2 、 H$_{3}^{+}$ 和 H 2 D + 的邻位和对位形式。我们的结果表明，在这种条件下的电离程度敏感地取决于晶粒尺寸分布，或更准确地说，取决于每个氢核的平均晶粒表面积。根据此参数和密度，主要离子可能是 H + 、H$_{3}^{+}$ 或 D$_{3}^{+}$。我们表明，在 L 1544 观测到的邻位 H 2 D + 的丰度可以用完整的耗尽模型来令人满意地解释，因此，该物种是前恒星核心运动学的重要示踪剂。
We have carried out calculations of ionization equilibrium and deuterium fractionation for conditions appropriate to a completely depleted, low mass pre-protostellar core, where heavy elements such as C, N, and O have vanished from the gas phase and are incorporated in ice mantles frozen on dust grain surfaces. We put particular emphasis on the interpretation of recent observations of H 2 D + towards the centre of the prestellar core L 1544 (Caselli et al. [CITE]) and also compute the ambipolar diffusion timescale. We consider explicitly the ortho and para forms of H 2 , H$_{3}^{+}$, and H 2 D + . Our results show that the ionization degree under such conditions depends sensitively on the grain size distribution or, more precisely, on the mean grain surface area per hydrogen nucleus. Depending upon this parameter and upon density, the major ion may be H + , H$_{3}^{+}$, or D$_{3}^{+}$. We show that the abundance of ortho-H 2 D + observed towards L 1544 can be explained satisfactorily in terms of a complete depletion model and that this species is, as a consequence, an important tracer of the kinematics of prestellar cores.