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arXiv 2007.06050astro-ph.SRastro-ph.EPastro-ph.GA
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原恒星坍缩：形成富含尘埃的原行星盘的条件

Protostellar collapse: the conditions to form dust rich protoplanetary disks

Ugo Lebreuilly, Benoît Commerçon, Guillaume Laibe

备注：
Accepted for publication in Astronomy & Astrophysics
发表信息：
A&A 641, A112 (2020)
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摘要：

尘埃在恒星、盘和行星形成过程中起着关键作用。然而，它在原恒星坍缩过程中的动力学仍然是一个研究不足的领域。最近的研究似乎表明，在这些早期阶段，尘埃可能会有效地与气体分离。我们的目标是了解在原恒星坍缩的早期阶段，尘埃颗粒集中在多少和哪些区域，并了解它如何取决于初始云和固体颗粒的性质。我们使用多个物种的尘埃动力学求解器的网格为基础的代码RAMSES进行各种模拟的尘埃崩溃。我们进行流体动力学和MHD模拟，我们改变最大晶粒尺寸，热重能量比和云的磁性。我们模拟了10个中性尘埃粒子的同时演化，粒子大小从几纳米到几百微米不等。我们获得了显着的去耦之间的气体和灰尘的颗粒的典型尺寸为几个10微米。这种退耦强烈地依赖于热-重力能量比、晶粒尺寸或是否包含磁场。与半解析模型校准我们的结果，我们表明，尘埃比主要是指数变化的初始斯托克斯数的速率，取决于当地的云属性。我们发现，较大的晶粒往往解决和漂移有效地在第一个核心和新形成的磁盘。这可能会产生数倍于初始值的粉尘与气体比率。粉尘在高密度区集中，在低密度区减少。颗粒与气体分离的大小取决于云的初始性质。由于尘埃不一定可以作为气体的代理在崩溃期间，我们强调的必要性，包括其动力学的治疗崩溃模拟。

英文摘要：

Dust plays a key role during star, disk and planet formation. Yet, its dynamics during the protostellar collapse remains a poorly investigated field. Recent studies seem to indicate that dust may decouple efficiently from the gas during these early stages. We aim to understand how much and in which regions dust grains concentrate during the early phases of the protostellar collapse, and see how it depends on the properties of the initial cloud and of the solid particles. We use the multiple species dust dynamics solver of the grid-based code RAMSES to perform various simulations of dusty collapses. We perform hydrodynamical and MHD simulations where we vary the maximum grain size, the thermal-to-gravitational energy ratio and the magnetic properties of the cloud. We simulate the simultaneous evolution of ten neutral dust grains species with grain sizes varying from a few nm to a few hundredth of microns. We obtain a significant decoupling between the gas and the dust for grains of typical sizes a few 10 microns. This decoupling strongly depends on the thermal-to-gravitational energy ratio, the grain sizes or the inclusion of a magnetic field. With a semi-analytic model calibrated on our results, we show that the dust ratio mostly varies exponentially with the initial Stokes number at a rate that depends on the local cloud properties. We find that larger grains tend to settle and drift efficiently in the first-core and in the newly formed disk. This can produce dust-to-gas ratios of several times the initial value. Dust concentrates in high density regions and is depleted in low density regions. The size at which grains decouple from the gas depends on the initial properties of the clouds. Since dust can not necessarily be used as a proxy for gas during the collapse, we emphasize on the necessity of including the treatment of its dynamics in collapse simulations.

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