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arXiv 1805.03215astro-ph.GAastro-ph.HEastro-ph.SR
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原恒星吸积激波中的Cosmic Ray加速和嵌入原团簇电离率模型的探索

Exploration of Cosmic Ray Acceleration in Protostellar Accretion Shocks and A Model for Ionization Rates in Embedded Protoclusters

Brandt A. L. Gaches, Stella S. R. Offner

摘要:

我们建立了一个模型,从原恒星吸积冲击宇宙线加速,并计算由此产生的宇宙线电离率在恒星形成的分子云。将原星团模型与解析吸积激波模型耦合,计算了宇宙线从原恒星表面的加速。我们提出了宇宙射线通量谱从keV到GeV的能量为一个典型的低质量原恒星。我们发现,在冲击表面的频谱遵循幂律的趋势,在6个数量级的能量。衰减后,高能量下的光谱变陡,而低能量下的光谱相对平坦。利用相对论质子计算了原恒星表面和核心边缘的宇宙线压力和电离率。我们提出的宇宙射线电离率为个别原恒星作为其瞬时质量和最终质量的函数。在吸积激波表面,原恒星宇宙线电离率为$ζ\approx 0.01 - 1$ s $^{-1}$。然而,在核心的边缘,宇宙射线电离率基本上下降到$ζ\approx 10^{-20}$到$10^{-17}$ s $^{-1}$之间。宇宙射线电离率存在较大的空间梯度,使得内部区域可能经历大于通常假设的基准率$ζ= 3\times10^{-17}$ s $^{-1}$的宇宙射线电离率。最后,我们计算了5个数量级以上的原恒星团的宇宙线电离率。我们发现,超过约200个原恒星的集群产生更高的宇宙射线电离率在其出生的云比基准银河值。

英文摘要:

We construct a model for cosmic ray acceleration from protostellar accretion shocks and calculate the resulting cosmic ray ionization rate within star-forming molecular clouds. We couple a protostar cluster model with an analytic accretion shock model to calculate the cosmic ray acceleration from protostellar surfaces. We present the cosmic ray flux spectrum from keV to GeV energies for a typical low-mass protostar. We find that at the shock surface the spectrum follows a power-law trend across 6 orders of magnitude in energy. After attenuation, the spectrum at high energies steepens, while at low energies it is relatively flat. We calculate the cosmic ray pressure and cosmic ray ionization rate from relativistic protons at the protostellar surface and at the edge of the core. We present the cosmic ray ionization rate for individual protostars as a function of their instantaneous mass and final mass. The protostellar cosmic ray ionization rate is $ζ\approx 0.01 - 1$ s$^{-1}$ at the accretion shock surface. However, at the edge of the core, the cosmic ray ionization rate drops substantially to between $ζ\approx 10^{-20}$ to $10^{-17}$ s$^{-1}$. There is a large spatial gradient in the cosmic ray ionization rate, such that inner regions may experience cosmic ray ionization rates larger than the often assumed fiducial rate, $ζ= 3\times10^{-17}$ s$^{-1}$. Finally, we calculate the cosmic ray ionization rate for protostellar clusters over 5 orders of magnitude of cluster size. We find that clusters with more than approximately 200 protostars produce a higher cosmic ray ionization rate within their natal cloud than the fiducial galactic value.

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