Characterization of the umbra-penumbra boundary by the vertical component of the magnetic field -- Analysis of ground-based data from the GREGOR Infrared Spectrograph
The vertical component of the magnetic field ($B_\perp$) was found to reach a constant value at the umbra-penumbra boundary of stable sunspots in a recent statistical study of Hinode/SP data. The objective of this work is to verify the existence of a constant value for $B_\perp$ at the umbra-penumbra boundary from ground-based data in the near-infrared wavelengths and to determine its value for GREGOR Infrared Spectrograph (GRIS) data. This is the first statistical study on the Jurcak criterion with ground-based data, and we compare it with the results from Hinode and HMI data. Eleven spectropolarimetric data sets from the GRIS slit-spectograph containing stable sunspots were selected from the GRIS archive (sdc.leibniz-kis.de). SIR inversions including a polarimetric straylight correction are used to produce maps of the magnetic field vector using the Fe 1564.8 and 1566.2 nm lines. Averages of $B_\perp$ along umbra-penumbra boundaries are analyzed for the 11 data sets. Geometric differences between contours at the resulting $B_\perp^{\rm const}$ value and contours in intensity, $ΔP$, are calculated. Averaged over the 11 sunspots, we find a value of $B_\perp=1787\pm100$ gauss. Contours at $B_\perp=B_\perp^{\rm const}$ and contours calculated in intensity maps match from a visual inspection and the geometric distance $ΔP$ was found to be on the order of 2 pixels. Furthermore, the standard deviation between different data sets of averages along umbra--penumbra contours is smaller for $B_\perp$ than for $B_\parallel$ by a factor of 2.4. Our results provide further support to the Jurcak criterion with the existence of an invariable value $B_\perp^{\rm const}$ at the umbra--penumbra boundary. We also found that the geometric difference, $ΔP$, between intensity contours and contours at $B_\perp=B_\perp^{\rm const}$ acts as an index of stability for sunspots.
Context. It is unclear why there is a rather sharp boundary in sunspots between the umbra and the penumbra. Both regions exhibit magnetoconvection, manifesting in penumbral filaments in the penumbra and in umbral dots in the umbra. Aims. Here we compare the physical properties of umbral dots and penumbral filaments. Our goal is to understand how the properties of these convective features change across the boundary between the umbra and the penumbra and how this is related to the rapid increase in brightness at the umbra-penumbra boundary. Methods. We derived ensemble averages of the physical …
Jurcak et al (2018) have reported that, in a sample of more than 100 umbral cores in sunspots, the umbral-penumbral boundary (UPB) is characterized by a remarkably narrowly-defined numerical value (1867 G) of the vertical component of the magnetic field. Gough and Tayler (1966), in their study of magneto-convection, showed that the onset of convection in the presence of a magnetic field is controlled by a parameter δ which also depends on the vertical component of the field. Combining the Jurcak et al result with various empirical models of sunspots leads us to propose the following hypothesis…
Observations of Supersonic Downflows Near the Umbra-Penumbra Boundary of Sunspots as Revealed by Hinode
Hinode的高分辨率分光偏振观测揭示了3个太阳黑子的本影-半影边界处存在超音速下降流，这是Louis等人（2010年）最近报道的。观察到这些下行流与明亮的半影细丝共空间，并占据大于1.6弧秒$^2$的面积。它们位于中心侧的半影，与太阳黑子具有相同的极性，这表明它们与Evershed Flow无关。在本文中，我们描述了在NOAA AR 10923中观测到的超声速，并讨论了光球以及色球增亮，这是靠近下降区。我们的观测结果表明，这种现象是由动态和充满活力的物理过程中的内部半影影响上覆的色球层，从而提供了新的见解太阳黑子的数值模型。
We study the long-term behaviour of sunspot penumbra to umbra area ratio by analyzing the recently digitized Kodaikanal white-light data (1923-2011). We implement an automatic umbra extraction method and compute the ratio over eight solar cycles (Cycles 16-23). Although the average ratio doesn't show any variation with spot latitudes, cycle phases and strengths, it increases from 5.5 to 6 as the sunspot size increases from 100 $μ$hem to 2000 $μ$hem. Interestingly, our analysis also reveals that this ratio for smaller sunspots (area $<$ 100 $μ$hem) does not have any long-term systematic trend w…
Context. It has been reported that the boundary between the umbra and the penumbra of sunspots occurs at a canonical value of the strength of the vertical magnetic field, independently of the size of the spot. This critical field strength is interpreted as to be the threshold for the onset of magnetoconvection. Aims. Here we investigate the reasons why this criterion, also called the Jurčák criterion in the literature, does not always identify the boundary between umbra and penumbra. Methods. We perform a statistical analysis of 23 sunspots observed with Hinode/SOT. We compare the properties o…
It was empirically determined that the umbra-penumbra boundaries of stable sunspots are characterized by a constant value of the vertical magnetic field. We analyzed the evolution of the photospheric magnetic field properties of a decaying sunspot belonging to NOAA 11277 between August 28 - September 3, 2011. The observations were acquired with the spectropolarimeter on-board of the Hinode satellite. We aim to proof the validity of the constant vertical magnetic-field boundary between the umbra and penumbra in decaying sunspots. A spectral-line inversion technique was used to infer the magneti…
To better understand the formation and decay of sunspot penumbra, we studied the evolution of sunspots in the three regions of the active-region NOAA 12673 in detail. The evolution of sunspots in the three regions were all involved in the interaction of two magnetic field systems: the pre-existing magnetic field system and the later emerging magnetic field system. Through analyzing the photospheric magnetic field properties, it is found that the formation of the penumbra originated from the newly emerging magnetic bipole that were trapped in the photosphere. The change of magnetic fields in pe…
The magnetograms of sixteen Active Regions, observed during June - November 2015, were obtained from the Joint Science Operations Center and used to determine the fractal dimensions of various magnetic field groups. The fields were divided into strong (positive and negative) and weak (positive and negative) groupings. The area-perimeter method was used to determine the fractal dimensions for the umbral and penumbral regions of the magnetograms. The fractal dimensions were found to be 1.79 \pm 0.49 and 1.96 \pm 0.29 for strong and weak magnetic fields respectively. When compared to the umbral a…
We analyse a sunspot simulation in an effort to understand the origin of the convective instabilities giving rise to the penumbral and umbral distinct regimes. We applied the criterion from Gough \& Tayler (1966), accounting for the stabilising effect of the vertical magnetic field to investigate the convective instabilities in a MURaM sunspot simulation. We find: (1) a highly unstable shallow layer right beneath the surface extending all over the simulation box in which convection is triggered by radiative cooling in the photosphere; (2) a deep umbral core (beneath -5 Mm) stabilised against o…
Precursor of Sunspot Penumbral Formation discovered with Hinode SOT Observations
我们目前的观测的一个间接的签名，这将有助于了解太阳黑子半影的形成过程。日之出太阳光学望远镜成功地捕捉到了一个太阳黑子从小孔到一个大的发育良好的太阳黑子的整个演化过程，其中半影出现在NOAA活动区11039的一个新兴通量区。我们发现在Ca II H图像中，在本影周围形成半影之前，围绕本影（孔）的环形区（宽度为3”-5”）。半影的发展似乎是为了填补环形区。环形带显示弱磁图信号，意味着那里的磁通量较小或磁场高度倾斜。移动预先存在的环境磁场岛，使其分布在环形区的外边缘，并且不进入该区域。在该区域没有强烈的系统性流动模式，但我们偶尔观察到小的磁通量斑块流出。观测结果表明，环形带不同于黑子沟流区，它代表了色球层的结构。我们的结论是，环形带反映了形成的磁冠覆盖在周围的区域在色球水平的本影，在光球水平的半影形成之前。半影的形成过程需要考虑色球层中的磁场结构。
Context. The solar chromosphere and the lower transition region is believed to play a crucial role in the heating of the solar corona. Models that describe the chromosphere (and the lower transition region), accounting for its highly dynamic and structured character are, so far, found to be lacking. This is partly due to the breakdown of complete frequency redistribution in the chromospheric layers and also because of the difficulty in obtaining complete sets of observations that adequately constrain the solar atmosphere at all relevant heights. Aims. We aim to obtain semi-empirical model atmo…
The aim of the present study is to show the varying asymmetries during the decay of sunspot groups. The source of input data is the SoHO/MDI-Debrecen Database (SDD) sunspot catalog that contains the magnetic polarity data for time interval 1996-2010. Several types of asymmetries were examined on the selected sample of 142 sunspot groups. The leading-following asymmetry increases in three phases during the decay and exhibits anticorrelation with size. It is also related to a hemispheric asymmetry, during the decay the area asymmetry index has higher values in the southern hemisphere which may b…
The analyses of sunspot observations revealed a fundamental magnetic property of the umbral boundary, the invariance of the vertical component of the magnetic field. We aim to analyse the magnetic properties of the umbra-penumbra boundary in simulated sunspots and thus assess their similarity to observed sunspots. Also, we aim to investigate the role of plasma $β$ and the ratio of kinetic to magnetic energy in simulated sunspots on the convective motions. We use a set of non-grey simulation runs of sunspots with the MURaM code. These data are used to synthesise the Stokes profiles that are the…
Upper Chromospheric Magnetic Field of a Sunspot Penumbra: Observations of Fine Structure
本文将探讨上色球层黑子半影磁场的精细结构，并与光球层的磁场进行比较。高空间分辨率分光偏振观测是用1.5米的GREGOR望远镜使用GREGOR红外光谱仪（GRIS）记录的。观测到的谱域包括色球上部He I三重态（1083.0 nm）和光球Si I 1082.7 nm和Ca I 1083.3 nm谱线。在Milne-Eddington型大气模型下，通过反演He I三重态得到了色球上层磁场。对Si I 1082.7 nm和Ca I 1083.3 nm谱线进行了与高度相关的反演，得到了光球磁场。我们发现磁场的倾角在光球层和上色球层都表现出方位角方向的变化。色球层的变化与光球场倾角的变化非常吻合，并且与半影光球层中众所周知的脊和脊间结构相似。发现上色球层磁场倾角的典型峰-峰变化为10-15度，即，大约是光球层变化的一半。相反，观测到的半影的磁场强度在上色球层的小空间尺度上并没有表现出变化。由于高空间分辨率的观测可能与格雷戈里望远镜在1.08微米，我们发现，突出的小尺度波动的磁场倾斜，这是一个显着的一部分，太阳黑子半影光球的属性，也坚持在色球层，虽然在有些减少的幅度。这种复杂的磁结构可能会促进半影色球动力学现象，如半影微喷流或瞬态亮点。
Solar active regions show a wide variety of oscillatory phenomena. The presence of the magnetic field leads to the appearance of several wave modes, whose behavior is determined by the sunspot thermal and magnetic structure. We aim to study the relation between the umbral and penumbral waves observed at the high photosphere and the magnetic field topology of the sunspot. Observations of the sunspot in active region NOAA 12662 obtained with the GREGOR telescope (Observatorio del Teide, Spain) were acquired on 2017 June 17. The data set includes a temporal series in the Fe I 5435 Å line obtained…
KRONOS II: Solar-like Umbra and Penumbra Properties on the Young Sun V1298~Tau
Michigan State University（密歇根州立大学）；Massachusetts Institute of Technology（麻省理工学院）；Arizona State University（亚利桑那州立大学）；Vanderbilt University（范德堡大学）；Max Planck Institute for Astronomy (MPIA)（马克斯·普朗克天文学研究所）；National Astronomical Observatory of Japan（日本国立天文台）
利用 JWST NIRISS/SOSS 掩星观测年轻行星 V1298 Tau bcd，通过星食事件光谱分析，发现宿主星 V1298~Tau 的黑子具有类似太阳的本影和半影结构，温度分别为 3265-3436 K 和 4388-4659 K，且本影面积占比约 30%。
Detection of emission in the Si i 1082.7 nm line core in sunspot umbrae
我们分析了分光偏振太阳黑子本影观测在近红外Si i 1082.7 nm线考虑NLTE效应。这些数据是用安装在德国GREGOR望远镜上的GRIS仪器获得的。一个点扩散函数（PSF）的构造使用之前的水星观测与GRIS和由自适应光学系统的GREGOR望远镜提供的信息。然后使用主成分分析反卷积方法从PSF中对数据进行反卷积，并通过NICOLE反演代码进行分析。在去除散射光的影响后，Si i 1082.7nm谱线似乎是在观测到的黑子本影中发射的。我们展示了本影轮廓的谱线形状如何随着散射光的量而发生显着变化。事实上，连续谱的强度范围平均从安静太阳连续谱强度的44%到大约20%。推断的水平与当前模型预测和经验本影模型一致。目前的本影经验模型不能再现在去卷积本影斯托克斯轮廓的排放。NLTE反演的结果表明，为了获得Si i 1082.7 nm谱线中的发射，温度分层应首先具有位于约log τ-2处的峰，并且当移动到过渡区时在较低的高度处开始上升。据我们所知，这是第一次在太阳黑子本影区的发射中看到Si i 1082.7 nm线。结果表明，目前本影模式的温度层结可能比预期的更复杂，过渡区位于太阳黑子本影上方较低的高度。我们的发现可能会提供深入了解为什么太阳黑子本影辐射在毫米光谱范围内是小于目前的经验本影模型预测。
12 stable single sunspots were investigated in two aspects. The outer boundaries of the sunspots umbra were determined by an independent mathematical method and the vertical component of the magnetic field at these boundaries was found. We analyzed data from the SDO station using the segments of the continuum and magnetic field. It is shown that in a wide range of sunspot fields, the field average along the contour changes weakly, while the vertical component of the magnetic field itself, in a particular spot, changes significantly along the defined contour which reflects the fibrous structure…
Leibniz-Institut für Astrophysik Potsdam (AIP)（波茨坦阿斯特罗物理莱布尼茨研究所）；Institut für Physik und Astronomie, Universität Potsdam（波茨坦大学物理与天文学研究所）；Institut für Sonnenphysik (KIS)（太阳物理研究所）；Hansa-Gymnasium（汉萨中学）；Instituto de Astrofísica de Canarias（加那利群岛天体物理研究所）；Universidad de La Laguna（拉古纳大学）；Udaipur Solar Observatory, Physical Research Laboratory（乌代浦尔太阳观测站，物理研究实验室）；Astronomical Institute of the Czech Academy of Sciences（捷克科学院天文研究所）
Physical Properties of a Sunspot Chromosphere with Umbral Flashes
我们提出了对太阳黑子本影闪光的新的高分辨率分光偏振Ca II 8542观测结果。在近0.18”，并跨越约一个小时的连续观察，这是迄今为止公布的最详细的数据集。我们的研究涉及LTE和非LTE反演（但也包括弱场分析作为健全性检查），以量化温度，质量流量和完整的磁场矢量几何形状。我们证实了早先的报道，超高频有非常精细的结构，热和冷的材料在亚弧秒尺度上混合。冲击波阵面比周围的物质热大约1000 K。我们没有观察到本影中的场的显著波动。然而，在半影中，运行的半影波的通过使磁场强度改变约200 G（峰-峰幅度），但它不改变场的方向（至少在我们几度的灵敏度内不显著）。我们发现对于视线速度和磁场强度，随着磁场倾斜度的增加，高频调制功率有减小的趋势。在外部半影中，我们发现没有高频功率，而朝向本影的高频功率越来越多。
There are no direct spatially resolved observations of spots on stars other than the Sun and starspot properties are inferred indirectly through lightcurves and spectropolarimetric data. We present the first self-consistent 3D radiative MHD computations of starspots on G2V, K0V and M0V stars, which will help to better understand observations of activity, variability and magnetic fields in late-type main-sequence stars. We used the MURaM code, which has been extensively used to compute "realistic" sunspots, for our simulations. We aim to study how fundamental starspot properties such as intensi…
We present a study of wave processes in the sunspot region NOAA 12670 on 2017 August 10 observed by the Goode Solar Telescope in the TiO 7057 A and Ha 6563 A spectral lines. To study the distribution of power oscillations and their dynamics, we applied the pixelized wavelet filtering (PWF) technique. For the first time, the spatial structure of oscillation sources as a footpoints of fine magnetic tubes, anchored in the sunspot umbra was obtained. We found that at the chromosphere level, emission variation is a combination of numerous independent oscillations located in the sources with small a…
