The magnetic and velocity fields of solar active regions; Proceedings of the 141th IAU Colloquium, Beijing, China, Sept. 6-12, 1992-猫眼课题宝

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1993

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H. Zirin;G. Ai;Haimin Wang

我们系统地描述了太阳黑子中斯托克斯线轮廓所表现出的不对称形状。这些不对称似乎是由太阳黑子光球层的磁场和速度梯度引起的。引言尽管自 60 年代以来就在太阳黑子中观察到了不对称的斯托克斯 Q、U 和 V 线剖面（例如，Kjeldseth-Moe 1967），但文献中没有对形状、星等的空间分布进行系统的研究。目前的工作描述了对这些斯托克斯轮廓的不对称性进行系统表征的首次尝试。我们还概述了潜在物理原因的初步解释。空间变化我们分析了在四个太阳区域 (125"xl25") 收集的 Stokes Q、U 和 V 剖面，每个太阳区域都包含一个大的、大致对称的太阳黑子（详细信息请参见 Lites & Skumanich 1990）。这些数据的基本观测参数为：谱线：Fel 630.25 nm。望远镜和旋光计：萨克拉门托峰的日冕仪以及 Stokes II HAO 旋光计（Baur 等人，1981）。光谱分辨率：~10 mA/像素，平滑至~35 mA。角分辨率：像素大小以及采样间隔 ~5" 。仪器偏振：可以忽略不计（详细信息请参阅 Sanchez Almeida & Lites 1992）。根据相应斯托克斯轮廓呈现的不对称类型，可以将每个太阳黑子分为三个区域：中心侧半影（最接近圆盘中心的半影）、本影和边缘侧半影。不过，从一个区域到另一个区域，线形状平滑变化。中心端使用条款，请参见 https://doi.org/10.1017/S0252921100029031 IP 地址：207.241.231.83，2018 年 7 月 27 日 15:38:03，遵守 Cambridge Core 178 J. SANCHEZ ALMEIDA 和 B. W. LITES 半影剖面显示，在肢体侧半影中，蓝色瓣更宽且幅度通常更低。图 1 显示了各种代表性的斯托克斯 V 半影轮廓。（边缘，中性线） -0.30 6302.0 _i_ 8302.8 6302.4 6302.6 波长 6302.8 8303.0 图 1. 太阳黑子不同部分中存在的斯托克斯 V 剖面形状（圆偏振与 A 中的波长）的各种典型示例我们尝试重现观测到的现象。引起磁场和速度的视线梯度的不对称性也可能导致斯托克斯剖面的不对称性；然而，它们不能产生宽带圆偏振太阳黑子（Makita & Ohki 1986 和其中的参考文献），我们发现，随着深度的增加，Evershed 流大致再现了观测到的不对称性。这种梯度符合上面引用的宽带圆偏振的经典图像，随着视线深入半影大气层，磁场线必须变得更加水平（详细信息请参见 Sanchez Almeida k Lites 1992）。 Fel 630.25 nm 的斯托克斯 Q、U 和 V 线剖面的不对称形状在太阳黑子之间系统地变化。这种变化似乎是由于 Evershed 流的大小随深度而增加所致。此外，宽带圆偏振的基本观测特性可在 https://www.cambridge.org/core/terms 上下载。 https://www.cambridge.org/core。IP 地址：207.241.231.83，2018 年 7 月 27 日 15:38:03，根据 Cambridge Core ASYMMETRIC STOKES Q、U 和 V 线剖面 179，如果除了 Evershed 流的这种变化之外，人们还假设半影磁场线随着光学深度的增加而变得更加水平。致谢本次研讨会上提出的技术和结果的详细讨论将出现在 Sanchez Almeida & Lites (1992) 的论文中。该工作部分由 DGICYT 项目 PB91-0530 资助，并由国家科学基金会赞助。罗杰斯，S.R. 1981，太阳物理学 70，395 Kjeldseth-Moe，1967 年，IAU Symp. 35 太阳活动区域的结构和发展，K.O.，Reidel，第 202 页兰多尔菲，M 1987，太阳物理学 109， fe Skumanich, A. 1990, Ap. J., 348, 747 Makita, M., & Ohki, Y. 1986, Ann. Tokyo Astron. Obs. 21, 1 Sanchez Almeida, J., & Lites B.W. 1992, Ap. J., 398，见 https://www.cambridge.org/core/terms。 https://doi.org/10.1017/S0252921100029031 从 https://www.cambridge.org/core 下载。IP 地址：207.241.231.83，2018 年 7 月 27 日 15:38:03，以剑桥核心为准。

We present a systematic description of the asymmetric shapes the Stokes line profiles exhibit in sunspots. These asymmetries seem to be caused by gradients of both magnetic field and velocity in the photospheres of sunspots. INTRODUCTION Although asymmetric Stokes Q, U and V line profiles have been observed in sunspots since the sixties (e.g., Kjeldseth-Moe 1967), no systematic study of the spatial distribution of shapes, magnitudes etc. exits in the literature. The present work describes a first attempt to give a systematic characterization of the asymmetries of these Stokes profiles. We also outline a fist order interpretation of the underlying physical cause. SPATIAL VARIATION We have analyzed Stokes Q, U and V profiles gathered in four solar regions (125"xl25"), each one containing a large, roughly symmetric, sunspot (see Lites & Skumanich 1990 for details). The basic observational parameters of these data are: Spectral line: Fel 630.25 nm. Telescope and polarimeter: the coronograph at Sacramento Peak together with the Stokes II HAO polarimeter (Baur et al. 1981). Spectral resolution: ~10 mA/pix smoothed to ~35 mA. Angular resolution: pixel size as well as sampling interval ~5" . Instrumental polarization: negligible (see Sanchez Almeida & Lites 1992 for details). One can divide each sunspot into three zones according to the type of asymmetry the corresponding Stokes profiles present there: the center-side penumbra (penumbra closest to the center of the disk), the umbra and the limb-side penumbra. Line shapes vary smoothly from one zone to another, though. Center-side terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0252921100029031 Downloaded from https://www.cambridge.org/core. IP address: 207.241.231.83, on 27 Jul 2018 at 15:38:03, subject to the Cambridge Core 178 J. SANCHEZ ALMEIDA AND B. W. LITES penumbral profiles show blue lobes broader and generally lower in amplitude than the red lobes. Red lobes turn out to be broader in the limb-side penumba. Finally, asymmetries become less pronounced in the umbral profiles. Fig. 1 shows various representative Stokes V profiles. 0.30 Umbra Penumbra (center) _ _ Penumbra (limb) Penumbra (limb, neutral line) -0.30 6302.0 _i_ 8302.8 6302.4 6302.6 Wavelength 6302.8 8303.0 Fig. 1. Various typical examples of the shapes the Stokes V profiles (circular polarization versus wavelength in A) present in different parts of the sunspot. GRADIENTS OF MAGNETIC FIELD AND VELOCITY We tried to reproduce the observed asymmetries invoking line-of-sight gradients of both magnetic field and velocity. Spatial inhomogeneities smaller than our resolution element might also cause the asymmetries of the Stokes profiles; nevertheless, they cannot produce the broad-band circular polarization sunspots generate (Makita & Ohki 1986 and references therein). Applying the inversion technique by Landolfi (1983), we find that an Evershed flow whose magnitude increases with depth roughly reproduces the observed asymmetric profiles. Such gradient fits within the classical picture of the Evershed flow. In order to reproduce the observed broad-band circular polarization quoted above, the magnetic field lines have to become more horizontal as the line-of-sight goes deeper into the penumbral atmosphere (see Sanchez Almeida k Lites 1992 for details). CONCLUSIONS The asymmetric shapes of the Stokes Q, U and V line profiles of Fel 630.25 nm vary systematically across sunspots: from the center-side penumbra through the umbra to the limb-side penumbra. Such variation seems to be due to the Evershed flow whose magnitude increases with depth. In addition, the basic observational properties of the broad-band circular polarization are reproduced terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0252921100029031 Downloaded from https://www.cambridge.org/core. IP address: 207.241.231.83, on 27 Jul 2018 at 15:38:03, subject to the Cambridge Core ASYMMETRIC STOKES Q, U AND V LINE PROFILES 179 if, on top of this variation of the Evershed flow, one assumes that the penumbral magnetic field lines become more horizontal as the optical depth increases. ACKNOWLEDGEMENTS A detailed discussion on the techniques and results presented at this colloquium will appear in the paper by Sanchez Almeida & Lites (1992). The work was partly funded by the DGICYT under project PB91-0530. The NCAR is sponsored by the National Science Foundation. REFERENCES Baur, T.G., Elmore, D.E., Lee, R.H., Querfeld, C.W., & Rogers, S.R. 1981, Solar Phys. 70, 395 Kjeldseth-Moe, 0 . 1967, in IAU Symp. 35 Structure and development of solar active regions, ed K.O. Kiepenheuer, Reidel, p. 202 Landolfi, M 1987, Solar Phys. 109, 287 Lites, B.W., fe Skumanich, A. 1990, Ap. J., 348, 747 Makita, M., & Ohki, Y. 1986, Ann. Tokyo Astron. Obs. 21, 1 Sanchez Almeida, J., & Lites B.W. 1992, Ap. J., 398, in press terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0252921100029031 Downloaded from https://www.cambridge.org/core. IP address: 207.241.231.83, on 27 Jul 2018 at 15:38:03, subject to the Cambridge Core

The magnetic and velocity fields of solar active regions; Proceedings of the 141th IAU Colloquium, Beijing, China, Sept. 6-12, 1992

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