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arXiv 0909.5552astro-ph.SR
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4247 A Sc II线太阳第二光谱的物理起源

On the physical origin of the second solar spectrum of the Sc II line at 4247 A

Luca Belluzzi

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8 pages, 8 figures, and 1 table. Accepted for publication in Astronomy and Astrophysics
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摘要：

Ba Ⅱ线在4554 A处的第二太阳光谱中所显示的线偏振轮廓的特殊三峰结构被解释为具有和不具有超精细结构（HFS）的钡同位素的不同贡献的结果。在相同的光谱中，在4247 A处的Sc II线中也观察到三峰偏振信号。钪具有单一稳定同位素（^{45}Sc），其由于核自旋I=7/2而显示HFS。我们调查的可能性，解释的线性偏振剖面中所示的第二个太阳光谱的Sc II线的HFS。假设一个具有HFS的二能级原子模型。采用光学薄板模型研究了原子极化和HFS的作用，避免了辐射转移效应带来的复杂性。假设板从下面照明的光球连续体，并在90度散射的辐射的偏振进行了研究。在这Sc II线中观察到的散射偏振分布的三峰结构不能完全解释在HFS方面。鉴于Sc II线在4247 A和Ba II线在4554 A之间的相似性，尚不清楚为什么在相同的建模假设下，只有钡线的三峰Q/I曲线可以用HFS完全解释。解释Sc II偏振信号的失败提出了一些重要的问题，这些问题的解决可能会导致我们对第二太阳光谱的理解的重大改进。特别是，如果Sc II信号的三峰结构实际上是由这里考虑的方法中忽略的物理机制产生的，那么不仅要识别这种机制，而且要理解为什么它在钡线的情况下似乎不那么重要，这将是非常有趣的。

英文摘要：

The peculiar three-peak structure of the linear polarization profile shown in the second solar spectrum by the Ba II line at 4554 A has been interpreted as the result of the different contributions coming from the barium isotopes with and without hyperfine structure (HFS). In the same spectrum, a triple peak polarization signal is also observed in the Sc II line at 4247 A. Scandium has a single stable isotope (^{45}Sc), which shows HFS due to a nuclear spin I=7/2. We investigate the possibility of interpreting the linear polarization profile shown in the second solar spectrum by this Sc II line in terms of HFS. A two-level model atom with HFS is assumed. Adopting an optically thin slab model, the role of atomic polarization and of HFS is investigated, avoiding the complications caused by radiative transfer effects. The slab is assumed to be illuminated from below by the photospheric continuum, and the polarization of the radiation scattered at 90 degrees is investigated. The three-peak structure of the scattering polarization profile observed in this Sc II line cannot be fully explained in terms of HFS. Given the similarities between the Sc II line at 4247 A and the Ba II line at 4554 A, it is not clear why, within the same modeling assumptions, only the three-peak Q/I profile of the barium line can be fully interpreted in terms of HFS. The failure to interpret this Sc II polarization signal raises important questions, whose resolution might lead to significant improvements in our understanding of the second solar spectrum. In particular, if the three-peak structure of the Sc II signal is actually produced by a physical mechanism neglected within the approach considered here, it will be extremely interesting not only to identify this mechanism, but also to understand why it seems to be less important in the case of the barium line.

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