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arXiv 1405.5142astro-ph.SR
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年轻嵌入星团产生的短寿命放射性核的分布

Distributions of Short-Lived Radioactive Nuclei Produced by Young Embedded Stellar Clusters

Fred C. Adams, Marco Fatuzzo, Lisa Holden

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52 pages, 13 figures, accepted to The Astrophysical Journal
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摘要：

银河系中大多数恒星的形成都发生在星团中，其中最大质量的成员可以影响其他太阳系的性质。本文考虑了星团如何通过超新星爆炸的核浓缩来影响恒星形成和形成行星系统，其中大质量恒星将短寿命的放射性核（SLR）传递到当地环境。这些原子核的衰变导致加热和电离，从而影响盘的演化，盘的化学，以及伴随的行星形成过程。核浓缩可以在两个空间尺度上发生：[1]在星团本身（$\ell\sim1$ pc）内，SLR被传递到与其他星团成员相关的星周盘。[2]在下一个更大的尺度（$\ell\sim2-10$ pc）上，SLR被注入背景分子云;这些原子核为附近的恒星形成区域和下一代盘提供加热和电离。对于第一种情况，我们构建了嵌入式集群提供的放射性富集水平的预期分布。星团可以解释早期太阳星云的SLR质量分数，但典型的SLR丰度要低$\sim10$倍。对于第二种情况，我们发现，分布富集的SLR分子云导致可比的丰度。对于直接和分布式富集过程，$^{26}$ Al和$^{60}$ Fe的质量传递到各个拱星盘通常落在$10-100pM_\odot$（其中$1pM_\odot=10^{-12}M_\odot$）的范围内。由SLR引起的相应电离速率通常落在$ζ_{SLR}\sim1-5\times10^{-19}$ sec $^{-1}$的范围内。该电离率小于由于宇宙射线引起的电离率，$ζ_{CR}\sim10^{-17}$ sec $^{-1}$，但是在宇宙射线衰减的区域（例如，盘中间平面）。

英文摘要：

Most star formation in the Galaxy takes place in clusters, where the most massive members can affect the properties of other constituent solar systems. This paper considers how clusters influence star formation and forming planetary systems through nuclear enrichment from supernova explosions, where massive stars deliver short-lived radioactive nuclei (SLRs) to their local environment. The decay of these nuclei leads to both heating and ionization, and thereby affects disk evolution, disk chemistry, and the accompanying process of planet formation. Nuclear enrichment can take place on two spatial scales: [1] Within the cluster itself ($\ell\sim1$pc), the SLRs are delivered to the circumstellar disks associated with other cluster members. [2] On the next larger scale ($\ell\sim2-10$pc), SLRs are injected into the background molecular cloud; these nuclei provide heating and ionization to nearby star-forming regions, and to the next generation of disks. For the first scenario, we construct the expected distributions of radioactive enrichment levels provided by embedded clusters. Clusters can account for the SLR mass fractions inferred for the early Solar Nebula, but typical SLR abundances are lower by a factor of $\sim10$. For the second scenario, we find that distributed enrichment of SLRs in molecular clouds leads to comparable abundances. For both the direct and distributed enrichment processes, the masses of $^{26}$Al and $^{60}$Fe delivered to individual circumstellar disks typically fall in the range $10-100pM_\odot$ (where $1pM_\odot=10^{-12}M_\odot$). The corresponding ionization rate due to SLRs typically falls in the range $ζ_{SLR}\sim1-5\times10^{-19}$ sec$^{-1}$. This ionization rate is smaller than that due to cosmic rays, $ζ_{CR}\sim10^{-17}$ sec$^{-1}$, but will be important in regions where cosmic rays are attenuated (e.g., disk mid-planes).

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