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磁场对原子能级占有数的影响与云南1米太阳塔偏振分析仪设计
Alternative TitleInfluence of Magnetic Fields on Level Populations of Atom and Design of Solar Polarimeter
胥成林
Subtype博士
Thesis Advisor屈中权
2006-08-11
Degree Grantor中国科学院研究生院(云南天文台)
Place of Conferral北京
Degree Discipline天体物理
Keyword太阳黑子 磁场 偏离因子 波尔兹曼分布 偏振仪
Abstract磁场,是研究太阳物理乃至天体物理的一个必不可少的课题。而对太阳磁场研究的重要性更为突出,毕竟太阳是离我们最近的一颗恒星,也是唯一一颗可供我们仔细研究的恒星。太阳黑子,作为太阳上的强磁场区域,是磁场在太阳大气中最明显的体现,同时也是一个巨大的磁场实验室。对太阳黑子的研究一方面使我们更了解磁场的本质属性,另一方面也有助于其它物理学科的发展。 本文分为两个部分。在第一部分里,我们首先利用云南天文台的太阳斯托克斯光谱望远镜(Solar Stokes Spectrum Telescope, S$^3$T)得到的Stokes光谱资料进行分析, 借助于原子能级对玻尔兹曼分布偏离的新定义(此定义直接可由连续源函数与线源函数之比得到),通过反演谱线Fe I 6302.5 的Stokes轮廓研究了磁场对原子能级占有数的影响。 我们定义的偏离因子和磁场间的关系说明了随着磁场增加,中性铁线6302.5$\AA$(Land\'{e} $g_{eff}=2.5$)的下能级的能级占有数成指数增长。这表明磁场能够对那些Land\'{e}因子非零的能级的原子占有数进行再分布。因此这种效应应该包含到统计平衡的计算中。此外,为了进一步证明这一激发关系与温度无关,我们在地面实验室里对发射线Hg I 5461$\AA$也做了磁场强度与能级占有数关系的研究。实验结果也证实了磁致激发的关系。最后通过考虑磁能在波尔兹曼分布中的作用解释了这一指数关系。 第二部分给出了云南1米太阳塔(YunNan Solar Telescope, YNST)偏振仪的设计方案。我们的设计对四条选定的谱线都具有很高的测量效率,这显示了该偏振仪优良的 消色差性能。这也保证了我们望远镜的科学目标的实现,即同时测量光球谱线和色球谱线。对于选定的四条谱线Fe I 525.06 nm,MgI 517.27 nm,和Fe I(630.15nm、630.25 nm),其总的偏振测量效率分别为1.0, 0.9999, 0.9691 和0.9691。同时我们也考虑了Stokes 各偏振分量的测量效率的平衡问题。另一方面,设计中的crosstalk也得到了很好的抑制,仅有$Q\rightarrow U$ 和 $U\rightarrow Q$的crosstalk存在,但是都比较小。根据我们的设计,偏振测量精度能够达到$ 3.0 \times10^{-4}$。最后我们对该偏振仪和国际上已经投入使用的偏振仪进行了比较,如TIP(或 LPSP)以及SOLIS使用的偏振仪。
Other AbstractMagnetic field's research is indispensable to solar physics and even to astrophysics. However, the research of solar magnetic field is more prominent. After all the sun is the nearest distance star from us, and it is also the only star carefully studied by us. As the active regions have strong magnetic fields, sunspot is the obvious embodiment where magnetic field is present in the solar atmosphere. At the same time, it also is a huge magnetic field lab. On the one hand, the research of sunspot makes us learning more properties of magnetic field. On the other hand, it also helps the development of the other's physical subjects. This paper is divided into two parts. In the first part, we present the influence of magnetic fields on the energy level populations of atoms by analyzing the Solar Stokes profiles of Fe{\sc I}6302.5$\AA$ forming in the solar magnetized atmosphere, with the aid of a departure factor defined to evaluate the deviation from the normal Boltzmann distribution without a magnetic field. This factor is directly related to the ratio of line source function to the continuum one. The relationship between the departure and the magnetic field reveals an effect that the magnetic field induces an exponential increase of the level population of the lower level of Fe{\sc I}6302.5 $\AA$($g_{eff}=2.5$) with the field strength. This indicates that the magnetic field can cause the redistribution of populations of those levels whose Land$\acute{e}$ factors are non-zero. Therefore, this effect should be included in the calculation of the statistical equilibrium. Otherwise, an experiment utilizing the Hg5461$\AA$ line in the laboratory on the earth is carried out to reveal that the exponential relation is independent of variations of temperature, and the excitation is completely magneto-induced. Finally, the exponential relation is explained by taking account of the magnetic energy in the Boltzmann distribution. In the second part, we outline the design of the polarimeter to be mounted in the 1m YunNan Solar Telescope (YNST). It has been shown that the achromatism of the design is satisfactory for the highly accurate measurement of the Solar Stokes spectra of the four selected lines. And this promises the realization of the scientific goals that the magnetic fields in both chromosphere and photosphere can be measured simultaneously. The total polarization measurement efficiencies are 1.0, 0.9999, 0.9691 and 0.9691 for the selected chromospheric line Mg I 517.27 nm, and the photospheric lines, i.e., the neutral iron lines 525.06 nm, 630.15nm and 630.25 nm respectively, while the balance among the efficiencies for the measurement of the Stokes polarization component $(Q,U,V)$ is sufficiently considered. On the other hand, the troublesome crosstalk is well suppressed, only the crosstalk $Q\rightarrow U$ and $U\rightarrow Q$ exist and they are small. This is very important to the calibration of the polarization measurement. According to the design, the polarimeter can realize the polarization measurement with high accuracy of about $< 3.0 \times 10^{-4}$. A comparison with other reference polarimeters, such as Polarimeter of Synoptic Optical Long-terms Investigation of the Sun (SOLIS) and Tenerife Infrared Polarimeter (TIP) and La Palma Stokes Polarimeter (LPSP), is carried out.
Subject Area天文学
Pages103
Language中文
Document Type学位论文
Identifierhttp://ir.ynao.ac.cn/handle/114a53/6596
Collection太阳物理研究组
Recommended Citation
GB/T 7714
胥成林. 磁场对原子能级占有数的影响与云南1米太阳塔偏振分析仪设计[D]. 北京. 中国科学院研究生院(云南天文台),2006.
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