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arXiv 1902.04586astro-ph.GAastro-ph.EPastro-ph.SR
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天鹅座OB2中原行星盘的外部光蒸发：连接盘与恒星形成动力学历史

External photoevaporation of protoplanetary discs in Cygnus OB2: linking discs to star formation dynamical history

Andrew J. Winter, Cathie J. Clarke, Giovanni P. Rosotti

备注：
20 pages, 17 figures, accepted by MNRAS
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摘要：

许多恒星形成于恒星密度增强的区域，其中恒星邻居的影响可能对原行星盘（PPD）的人口产生强烈的影响。特别是，来自大质量恒星的远紫外线（FUV）通量驱动来自PPD外缘的热风，加速了盘的破坏。在这项工作中，我们提出了一种新的技术，用于约束恒星形成环境的动力学历史，在强FUV照射的环境中使用PPD属性。应用最近的模型FUV引起的质量损失率的PPD人口的天鹅座OB 2，我们约束多久以前原始气体被驱逐出该地区; $ 0.5$百万年前，如果Shakura & Sunyaev $α$ -粘度参数是$α= 10^{-2}$（对应于一个粘性的时间尺度为$τ_\mathrm{visc} \approx 0.5$百万年的光盘的规模半径$40$ au周围的$1\, M_\odot$星）。$α$的这个值实际上是上限，因为它假设FUV光子在整个嵌入阶段有效地消光。有了这个气体排出时间尺度，我们能够产生一个完整的动力学模型，适合运动学和形态学数据以及光盘分数。我们认为天鹅座OB 2最初是由不同的大质量团块或细丝组成的，每个团块或细丝的质量都是恒星质量$\sim 10^4 \, M_\odot$。最后，我们预测，在有效的FUV引起的质量损失，光盘质量$M_\mathrm{disc}$作为恒星主机质量$m_\mathrm{star}$的函数遵循幂律与$M_\mathrm{disc} \propto m_\mathrm{star}^β$，其中$β\gtrsim 2.7$（取决于光盘初始条件和FUV曝光）。这是陡峭的比观察到的相关性在中等FUV通量（$1 < β<1.9$）的地区，并提供了一个有前途的诊断，以建立外部光蒸发在给定区域的影响。

英文摘要：

Many stars form in regions of enhanced stellar density, wherein the influence of stellar neighbours can have a strong influence on a protoplanetary disc (PPD) population. In particular, far ultraviolet (FUV) flux from massive stars drives thermal winds from the outer edge of PPDs, accelerating disc destruction. In this work, we present a novel technique for constraining the dynamical history of a star forming environment using PPD properties in a strongly FUV irradiated environment. Applying recent models for FUV induced mass loss rates to the PPD population of Cygnus OB2, we constrain how long ago primordial gas was expelled from the region; $ 0.5$ Myr ago if the Shakura & Sunyaev $α$-viscosity parameter is $α= 10^{-2}$ (corresponding to a viscous timescale of $τ_\mathrm{visc} \approx 0.5$ Myr for a disc of scale radius $40$ au around a $1\, M_\odot$ star). This value of $α$ is effectively an upper limit, since it assumes efficient extinction of FUV photons throughout the embedded phase. With this gas expulsion timescale we are able to produce a full dynamical model that fits kinematic and morphological data as well as disc fractions. We suggest Cygnus OB2 was originally composed of distinct massive clumps or filaments, each with a stellar mass $\sim 10^4 \, M_\odot$. Finally we predict that in regions of efficient FUV induced mass loss, disc mass $M_\mathrm{disc}$ as a function of stellar host mass $m_\mathrm{star}$ follows a power law with $M_\mathrm{disc} \propto m_\mathrm{star}^β$, where $β\gtrsim 2.7$ (depending on disc initial conditions and FUV exposure). This is steeper than observed correlations in regions of moderate FUV flux ($1 < β<1.9$), and offers a promising diagnostic to establish the influence of external photoevaporation in a given region.

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