High-resolution observations of the solar photosphere have recently revealed the presence of elongated filamentary bright structures inside sunspot umbrae. These features, which have been called umbral filaments (UFs), differ in morphology, evolution, and magnetic configuration from light bridges that are usually observed to intrude in sunspots.
To study an UF observed in the leading sunspot of active region NOAA 12529, we have analyzed spectro-polarimetric observations taken in the photosphere with the spectropolarimeter (SP) aboard the Hinode satellite. High-resolution observations in the upper chromosphere and transition region taken with the IRIS telescope and observations acquired by SDO/HMI and SDO/AIA have been used to complement the spectro-polarimetric analysis.
The results obtained from the inversion of the Hinode/SP measurements allow us to discard the hypothesis that UFs are a kind of light bridge. In fact, we find no field-free or low-field strength region cospatial to the observed UF. In contrast, we detect in the structure Stokes profiles that indicate the presence of strong horizontal fields, larger than 2500 G. Furthermore, a significant portion of the UF has opposite polarity with respect to the hosting umbra. In the upper atmospheric layers, we observe filaments being cospatial to the UF in the photosphere. We interpret these findings as suggesting that the UF could be the photospheric manifestation of a flux rope hanging above the sunspot, which triggers the formation of penumbral-like filaments within the umbra via magneto-convection.
Umbral flashes are periodic brightness increases routinely observed in the core of chromospheric lines within sunspot umbrae and are attributed to propagating shock fronts. In this work we quantify the shock heating energy of these umbral flashes using observations in the near infrared He I triplet obtained on 2014 December 7 with the SpectroPolarimetric Imager for the Energetic Sun (SPIES), which is a novel integral field unit spectrograph at the Dunn Solar Telescope. We determine the shock properties (the Mach number and the propagation speed) by fitting the measured He I spectral profiles w…
Umbral flashes (UFs) are emissions in the core of chromospheric lines caused by upward propagating waves steepening into shocks. UFs are followed by an expanding blue shifted umbral wave (UW) and red-shifted plasma returning to the initial state. Here we use 5 s cadence images acquired at $\pm$0.04~nm off the Halpha line center by the Visible Imaging Spectrometer (VIS) installed on the Goode Solar Telescope (GST) to detect the origin of UFs and UWs in a sunspot with a uniform umbra free of LBs and clusters of umbral dots. The data showed that UFs do not randomly originate over the umbra. Inste…
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。
Combining high-resolution spectropolarimetric and imaging data is key to understanding the decay process of sunspots as it allows us scrutinizing the velocity and magnetic fields of sunspots and their surroundings. Active region NOAA 12597 was observed on 24/09/2016 with the 1.5-m GREGOR solar telescope using high-spatial resolution imaging as well as imaging spectroscopy and near-infrared (NIR) spectropolarimetry. Horizontal proper motions were estimated with LCT, whereas LOS velocities were computed with spectral line fitting methods. The magnetic field properties were inferred with the SIR …
Chromospheric observations of sunspot umbrae offer an exceptional view of magneto-acoustic shock phenomena and the impact they have on the surrounding magnetically-dominated plasma. We employ simultaneous slit-based spectro-polarimetry and spectral imaging observations of the chromospheric He I 10830Å and Ca II 8542Å lines to examine fluctuations in the umbral magnetic field caused by the steepening of magneto-acoustic waves into umbral flashes. Following the application of modern inversion routines, we find evidence to support the scenario that umbral shock events cause expansion of the embed…
Spectro-polarimetric simulations of the solar limb: absorption-emission FeI $6301.5\mathrmÅ$ and $6302.5\mathrmÅ$ line profiles and torsional flows in the intergranular magnetic flux concentrations
Recent observations of the solar photosphere revealed the presence of elongated filamentary bright structures inside sunspot umbrae, called umbral filaments (UFs). These features differ in morphology, magnetic configuration, and evolution from light bridges that are usually observed to intrude in sunspots. To characterize an UF observed in the umbra of the giant leading sunspot of active region NOAA 12529, we analyze high-resolution observations taken in the photosphere with the spectropolarimeter aboard the Hinode satellite and in the upper chromosphere and transition region with the IRIS tel…
We report the discovery of a brightness enhancement in the center of a large sunspot umbra at a wavelength of 3 mm using the Atacama Large Millimeter/sub-millimeter Array (ALMA). Sunspots are amongst the most prominent features on the solar surface, but many of their aspects are surprisingly poorly understood. We analyzed a λ=3 mm (100 GHz) mosaic image obtained by ALMA, which includes a large sunspot within the active region AR12470 on December 16, 2015. The 3 mm map has a field-of-view and spatial resolution, which is the highest spatial-resolution map of an entire sunspot in this frequency …
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…
Spectro-Polarimetric Properties of Small-Scale Plasma Eruptions Driven by Magnetic Vortex Tubes
太阳对流的高度湍流性质导致了次表层与光球层和色球层之间强烈的多尺度相互作用。根据真实的三维辐射MHD数值模拟无处不在的小尺度涡管产生的湍流下可见的表面和集中在颗粒间的车道。涡管可以捕获和放大磁场，穿透色球层，并引发准周期性的流动爆发，产生Alfvénic波，将质量和能量输送到太阳大气中。模拟揭示了高速流动模式，复杂的热力学和磁结构的爆发涡流管。近地层强烈的压力梯度是自发喷发的启动和驱动力，而低色球层的洛伦兹力则加速了自发喷发。在本文中，模拟数据被用来进一步调查的喷发，其光谱偏振特性的Fe I 6301.5和6302.5 A谱线的动力学，并展示预期的签名的喷发日出SP数据。我们发现，复杂的动力学结构的涡管（在涡核和周边的上升流下降）可以捕捉到的斯托克斯I型。在喷发过程中，下降流和上升流的比例会突然改变，这种效应可以在斯托克斯V剖面中观察到。此外，在喷发期间，线偏振信号增加，这也可以用Hinode SP检测到。
New assignments of the CaH $A^{2}Π-X^{2}Σ^{+}$ transitions in the sunspot umbral spectrum and effective temperature estimation using molecular lines
The Graduate University for Advanced Studies, SOKENDAI（高级研究大学院大学）；National Astronomical Observatory of Japan（日本国立天文台）；Astrobiology Center（天体生物学中心）；University of Toyama（富山大学）；Subaru Telescope, National Astronomical Observatory of Japan（昴星望远镜，日本国立天文台）；Kyoto University（京都大学）
We analyze spectropolarimetric sunspot umbra observations taken in the near-infrared Si i 1082.7 nm line taking NLTE effects into account. The data were obtained with the GRIS instrument installed at the German GREGOR telescope. A point spread function (PSF) was constructed using prior Mercury observations with GRIS and the information provided by the adaptive optics system of the GREGOR telescope. The data were then deconvolved from the PSF using a principal component analysis deconvolution method and were analyzed via the NICOLE inversion code. The Si i 1082.7 nm line seems to be in emission…
In sunspot umbrae, convection is largely suppressed by the strong magnetic field. Previous measurements reported on negligible convective flows in umbral cores. Based on this, numerous studies have taken the umbra as zero reference to calculate Doppler velocities of the ambient active region. To clarify the amount of convective motion in the darkest part of umbrae, we directly measured Doppler velocities with an unprecedented accuracy and precision. We performed spectroscopic observations of sunspot umbrae with the Laser Absolute Reference Spectrograph (LARS) at the German Vacuum Tower Telesco…
The umbral oscillations of velocity are commonly observed in the chromosphere of a sunspot. Their sources are considered to be either the external p-mode driving or the internal excitation by magnetoconvection. Even though the possibility of the p-mode driving has been often considered, the internal excitation has been rarely investigated. We report the identification of the oscillation patterns that may be closely related to the events of internal excitation from the observations of velocity oscillations in the temperature minimum region of two sunspots. The velocities were determined from th…
This paper is devoted to the primary spectro-polarimetric observation performed at the New Vacuum Solar Telescope of China since 2017, and our aim is to precisely evaluate the real polarimetric accuracy and sensitivity of this polarimetry by using full Stokes spectro-polarimetric observations of the photospheric line Fe I 532.4 nm. In the work, we briefly describe the salient characteristic of the NVST as a polarimeter in technology and then characterize its instrumental polarization based on the operation in 2017 and 2019. It is verified that the calibration method making use of the instrumen…
The Visible Spectro-Polarimeter (ViSP) of the NSF Daniel K. Inouye Solar Telescope (DKIST) collected its Science Verification data on May 7-8, 2021. The instrument observed multiple layers of a sunspot atmosphere simultaneously, in passbands of Ca-II 397 nm (H-line), Fe-I 630 nm, and Ca-II 854 nm, scanning the region with a spatial sampling of 0.041" and average temporal cadence of 7.76 seconds, for a 38.8 minute duration. The slit moves southward across the plane-of-the-sky at 3.83 km/s. The spectropolarimetric scans exhibit prominent oscillatory 'ridge' structures which lie nearly perpendicu…
Some of the white dwarfs exhibit among the strongest magnetic fields in the universe. Many of these degenerate magnetic stars are also rotating very slowly. Among these objects, Grw+70$^\circ$\,8247, with its century-long suspected rotation period and its 400\,MG magnetic field, stands as a particularly interesting object. Surprisingly, for this star, the first white dwarf in which a magnetic field was discovered, no spectropolarimetric observations have been discussed in the literature in the last 40 years. Here we present two sets of linear and circular polarisation spectra taken in 2015 and…
We analyze spectropolarimetric observations of the chromospheric Ca II 8542 line taken by the Interferometric Bidimensional Spectrometer (IBIS) at the Dunn Solar Telescope and photospheric Fe I 6302 lines obtained with the Solar Optical Telescope (SOT) of Spectro-polarimeter (SP) on board the Hinode satellite. The data were obtained on 2012 January 29 targeting NOAA active region (AR) 11408 and AR 11410. By using the center-of-gravity (COG) method we compute the line-of-sight (LOS) field strength for observed lines of Fe I 6301.5/6302.5 with SP spacecraft at every places in the active region. …
The Interface Region Imaging Spectrograph (IRIS) mission provides high-resolution observations of the chromosphere and transition region. We try to determine whether the light walls exist somewhere else in active regions besides light bridges. Employing half-year high tempo-spatial data from the IRIS, we find lots of light walls either around sunspots or above light bridges. For the first time, we report one light wall near an umbral-penumbral boundary and another along a neutral line between two small sunspots. These new observations reveal that these light walls are multi-layer and multi-the…
Polarimetric and spectropolarimetric observations with FoReRo2: Instrument overview and standard star monitoring
Institute of Astronomy and National Astronomical Observatory, Bulgarian Academy of Sciences（保加利亚科学院天文研究所和国家天文台）；Armagh Observatory and Planetarium（阿马赫天文馆和天文台）
Magnetic field couples the solar interior to the solar atmosphere, known as the corona. The coronal magnetic field is one of the crucial parameters which determines the coronal structures and regulates the space weather phenomena like flares, coronal mass ejections, energetic particle events, and solar winds. Measuring the magnetic field at middle and higher coronal heights are extremely difficult problem and to date there is no single measurement technique available to measure the higher coronal magnetic fields routinely. polarization measurements of the low-frequency radio emissions are an i…
Chromospheric Dynamics of an Umbral Flare Kernel - Based on Coordinated SUNRISE III SCIP and Domeless Solar Telescope Observations
Kyoto University（京都大学）；Nagoya University（名古屋大学）；Kanazawa University（金泽大学）；Max-Planck-Institut für Sonnensystemforschung（马克斯·普朗克太阳系统研究所）；National Astronomical Observatory of Japan（日本国立天文台）；The University of Tokyo（东京大学）；The Graduate University for Advanced Studies (SOKENDAI)（高级研究大学院大学）
本研究利用SUNRISE III SCIP与DST的协同观测，揭示了太阳黑子本影内M1.4级耀斑核的色球精细结构与等离子体运动，解释了耀斑红不对称性的成因。
Context. Magnetic reconnection during flares takes place in the corona but a substantial part of flare energy is deposited in the chromosphere. However, high-resolution spectro-polarimetric chromospheric observations of flares are very rare. The most used observables are Ca II 8542 Å and He I 10830 Å. Aims. We aim to study the chromosphere during a C3.6 class flare via spectro-polarimetric observations of the He I D3 line. Methods. We present the first SST/CRISP spectro-polarimetric observations of He I D3. We analyze the data using the inversion code HAZEL, and estimate the LOS velocity and t…
Exploring the long-term temporal variability in polarization through multi-epoch optical spectro-polarimetry - Part I: A sample of Herbig Ae/Be and classical Be stars
Physical Research Laboratory（物理研究实验室）；Indian Institute of Technology Gandhinagar（甘地纳加尔印度理工学院）
Observational astrophysics started when spectroscopy could be applied to astronomy. Similarly, observational work on stellar magnetic fields became possible with the application of spectro-polarimetry. In recent decades there have been dramatic advances in the observational tools for spectro-polarimetry. The four Stokes parameters that provide a complete representation of partially polarized light can now be simultaneously imaged with megapixel array detectors with high polarimetric precision (0.001% in the degree of polarization). This has led to new insights about the nature and properties o…
Exploring the long-term temporal variability in polarization through multi-epoch optical spectro-polarimetry - Part II: A sample of symbiotic and red-giant stars
Physical Research Laboratory（物理研究实验室）；Indian Institute of Technology Gandhinagar（甘地纳加尔印度理工学院）；Johns Hopkins University（约翰斯·霍普金斯大学）；NASA Goddard Space Flight Center（美国国家航空航天局戈达德航天飞行中心）
