Photospheric Stratification of a Central Umbral Dot Using Stokes Profiles Recorded by Hinode: A Different Single-Case Study

We aim to study the physical nature of a central umbral dot (UD) close to disk center by analyzing full-Stokes spectra of the two Fe?i lines at 630 nm recorded by the spectropolarimeter on Hinode. Thermal and magnetic properties of the UD were directly inferred from Stokes profiles. Then, we applied the inversion code SIR to retrieve a single-component magnetic model atmosphere that recovers the observed full-Stokes profiles. The inversion results and direct inferences from the iron line pair are consistent. The studied UD does not show any signatures of upflows, but tends to show downflows. At the deeper-half of the photosphere (logτ>?1.0), the UD exhibits rapid changes in temperature with respect to its surroundings. The UD has a large magnetic field strength of about 3000 G without significant reduction at its center. Magnetic field lines are more vertical and twisted in the UD area than in the magnetic field of its surroundings. To explain the observational findings, we propose that the UD perturbs the funnel magnetic field of the umbra, making a tilt-ankle-knee configuration. A new interesting inference, deduced from the blending spectral lines in the observed wavelength interval, is that the shape and surface span of the UD in normalized intensity filtergrams computed at the core of the blending lines differ from the UD area seen in continuum intensity and in the filtergrams computed at the core of the iron line pair.     

Umbral flares

H flare patches usually do not occur in sunspot umbrae. Presented here are cases of a type of umbral flare in which the flare patch originated in, and was confined to, the p spot umbra. All are H subflares. Two of the four flares were accompanied by type III radio bursts. The simplicity and similarity of the magnetic fields of these regions were striking.     

太阳黑子本影振荡的多波段观测

基于多波段的观测数据, 研究了黑子本影振荡在太阳大气不同高度或温度的振荡特征. 目标黑子发生在2017年9月15日, 位于活动区12680. 多波段的观测数据包括AIA (Atmospheric Imaging Assembly)的极紫外成像及IRIS (Interface Region Imaging Spectrograph)的紫外光谱和成像. 在太阳黑子的本影位置, AIA 1700 Å 光变曲线的振荡周期约为(4.2士0.8) min,而AIA 1600 Å、171 Å和193 Å光变曲线的振荡周期约为(2.8士0.3)min. IRIS的Mg II h和k谱线及远紫外成像(2796 Å)都表现为(3.1士0.5) min的准周期振荡,而谱线Si IV 1393.76 Å的振荡周期约为(2.9+0.4)min.观测结果说明黑子本影的振荡周期随着太阳大气高度的升高而逐渐减小.较短的周期可认为是3 min振荡,很可能与黑子本影上方的慢磁声波有关,它起源于温度极小区并向上传播到日冕.较长的周期可解释为光球的5 min振荡,与太阳的P模振荡有关.     

Umbral oscillations in a detailed model umbra

Our theory of umbral oscillations as resonant modes of magneto-atmospheric waves (Scheuer and Thomas, 1981) is extended and confirmed by calculating the resonant modes in a much more detailed model of the umbral atmosphere. The depths of forcing required to produce observed oscillation periods (roughly 140 to 185 s) are in good agreement with the depths of overstable convection found in other studies (Moore, 1973; Mullan and Yun, 1973).     

A Flare and Umbral Flashes in a Sunspot

We studied the evolution and dynamic processes in the chromosphere above a sunspot umbra. A relatively rarely occurring phenomenon of bright long-lasting emission observed in the umbra of a unipolar sunspot of the AR 9570 group on August 11, 2001 was investigated. It was found that during the course of the observation, emission was spreading, gradually occupying nearly the entire sunspot umbra. Based on the analysis of the observations from other observatories, we arrived at the conclusion that the bright emission was a sympathetic flare that occurred in the sunspot umbra. It was assumed that there occurred an interaction with a neighboring, rapidly evolving group that exhibited subflares on the day of observation. In the same umbra, there was taking place an oscillatory process of the type of umbral flash (observations from August 11 and 12, 2001). The characteristics of the oscillatory process in the presence of the flare were studied. As the bright emission propagated in the sunspot umbra, brightness fluctuations ceased to be seen in the umbral flashes against the background of this brighter emission. The character of velocity variations did not change substantially, although the oscillation amplitude did decrease.     

Umbral intensities of large sunspots

It is proposed that present observations of the chromosphere and transition region in EUV, optical and mm wavelengths are best described by a three-component concept. The three components are taken to be: the interiors of supergranular cells, the hot plagettes overlying faculae, and the cooler, transient mottles which surround them in the network boundaries. The enhanced emission of the hot plagettes in transition ions is interpreted as a direct result of the increased pressure scale height over faculae relative to the cell interiors.     

Physical Characteristics of Umbral Dots Derived from a High-Resolution Observations

Solar Physics - We study the features of the magnetic field variations within the 2011 June 7 eruptive event that includes a large filament eruption, a flare, and a CME formation. The magnetic...     

Oscillations in the Umbral Atmosphere

The results of simultaneous observations of oscillations in the chromosphere, transition region, and corona above nine sunspots are presented. The data are obtained through coordinated observing with the Solar and Heliospheric Observatory — SOHO and the Transition Region And Coronal Explorer — TRACE. Oscillations are detected above each umbra. The power spectra show one dominant frequency corresponding to a period close to 3 min. We show that the oscillations in the sunspot transition region can be modeled by upwardly propagating acoustic waves. In the corona the oscillations are limited to small regions that often coincide with the endpoints of sunspot coronal loops. Spectral observations show that oscillations in the corona contribute to the observed oscillations in the TRACE 171 Å channel observations. We show that a recent suggestion regarding a connection between sunspot plumes and 3-min oscillations conflicts with the observations.     

Umbral oscillations in the presence of a spreading magnetic field

Résumé Des onze observatoires qui, depuis 1947, ont à des degrés divers participé à l'obtention de données coronales au coronographe, six seulement sont encore en service. Rendues homogènes à partir d'un traitement statistique, ces données permettraient de couvrir trente cinq années d'activité solaire, soit près de quatre cycles complets. Une exploitation intéressante de ces mesures est la recherche des trous coronaux (autre que polaires), sources du vent solaire à haute vitesse dont les retombées en matière d'accroissement de nos connaissances sur la physique de la haute atmosphère et relations avec le climat terrestre sont primordiales. De nombreuses résolutions récentes de symposium ont conclu en ce sens et il serait bon que les commissions spécialisées concernées de l'UAI se prononcent sur ce problème au cours de l'une de ses prochaines réunions.

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Thirty-five years of patrol measurements of the intensity of the solar corona outside eclipses

A review of the various observatories having done daily measurements of the activity of the solar corona and having regularly published their results is being given hereby. Out of eleven observatories having taken out to the observation campaign since 1947, only six are still working in this field. Due to the fact that the scales, the focus and photometric systems are not always the same, the measurements are not homogeneous and directly comparable. However, astronomers can find there a great lot of statistical data covering thirty five years of coronal activity, that is more than three solar cycles. Some of these data, such as those of the Pic-du-Midi observatory, are readily available on magnetic tapes and may be asked from the authors. One of the most interesting exploitations of these data is the search of coronal holes (other than polar holes which are simply the signature of the periodic activity of corona) and it is shown here that such features are easily detectable. So, it will be vital for future research in solar physics, and especially in solar weather and climate relationships (bearing in mind that coronal holes are the sources of high speed streamers of the solar wind which interacts with the Earth magnetosphere), to ensure continuity and quality of patrol ground-based corona intensities outside eclipses. A number of recent conclusions of symposia in this field have led to such recommendations, and it would be suitable if next specialized commissions of IAU meetings were to think about that matter.

     

Enhanced Joule Heating in Umbral Dots

We present a study of magnetic fields in umbral dots (UDs) and its consequences on the Joule heating of the UDs. Hamedivafa (Astron. Astrophys. 407, 761, 2003) studied the Joule heating using the vertical component of the magnetic field. In this paper the magnetic field profile in the UDs is investigated by including a new azimuthal component of the magnetic field that might explain a relatively large enhancement of Joule heating causing higher brightness near the circumference of the UDs.     

Umbral oscillations measured in the Stokes-V inversion point

The inversion point of the circular Zeeman polarization profile (V-Stokes) parameter is used to observe umbral Doppler oscillations free from disturbing influences of parasitic light. In a second step, purely umbral lines are used to avoid remaining influences from the V-profile of the (oscillating) penumbra. Among a total of nine sunspot umbrae, three exhibit oscillations within the various 1.5 to 2.5 hr samples. The periods differ significantly from 300 s, vary with time, and occur within time intervals of high tranquility thus explaining the lack of oscillations in the remaining sunspots.     

Umbral oscillations as resonant modes of magneto-atmospheric waves

Umbral oscillations in sunspots are identified as a resonant response of the umbral atmosphere to forcing by oscillatory convection in the subphotosphere. The full, linearized equations for magneto-atmospheric waves are solved numerically for a detailed model of the umbral atmosphere, for both forced and free oscillations. Resonant fast modes are found, the lowest mode having a period of 153 s, typical of umbral oscillations. A comparison is made with a similar analysis by Uchida and Sakurai (1975), who calculated resonant modes using an approximate (quasi-Alfvén) form of the wave equations. Whereas both analyses give an appropriate value for the period of oscillation, several new features of the motion follow from the full equations. The resonant modes are due to upward reflection in the subphotosphere (due to increasing sound speed) and downward reflection in the photosphere and low chromosphere (due to increasing Alfvén speed); downward reflection at the chromosphere-corona transition is unimportant for these modes.     

云南天文台观测到的黑子本影点

本文报道了国内首次对黑子本影细节的直接照相观测。通过对这些本影细节的形态的考察和对它们的平均视大小的粗略估计,认为其中一些是本影点。本文还讨论了它们与黑子发展演化过程的关系及其它有关问题。     

Occurrence of AlO Molecular Lines in Sunspot Umbral Spectra

Aluminium monoxide (AlO) is widely known for its astrophysical significance. An analysis of the prominent lines of the (2,3;3,2;3,4;4,5;4,3;5,6;6,7) bands of the B ²Σ⁺?X ²Σ⁺ transition with those of sunspot umbral spectral lines suggests that the AlO molecule appears to be a non-negligible component of sunspot umbrae. Results of a recent (2008) rotational analysis were used to carry out the study. The effective rotational temperature determined for the above lines in the sunspot umbral spectrum is found to be of the order of 2900 K. The radiative-transition parameters that include Franck–Condon (FC) factors, r-centroids, electronic-transition moment, Einstein coefficient, absorption–band oscillator strength, and radiative lifetime have been estimated for the experimentally known vibrational levels using the Rydberg–Klein–Rees (RKR) potential.     

Presence of C2 molecular Lines in Sunspot Umbral Spectra

The C₂ molecule is well known for its astrophysical importance. The radiative transition parameters that include Franck-Condon (FC) factor, r-centroid, electronic transition moment, Einstein coefficient, absorption band oscillator strength, effective temperatures and radiative life time have been estimated for the Swan band $(d^3{\Pi }_g-a^3{\Pi }_u)$ system of C₂ molecule for experimentally observed vibrational levels using RKR (Rydberg–Klein–Rees) potential energy curve. The lifetime for the d³Π_g state of C₂ molecule was found to be 82.36 ns for the $v^{\prime }=0$ level. A reliable numerical integration method has been used to solve the radial Schrödinger equation for the vibrational wave functions of upper and lower electronic states based on the latest available spectroscopic data and known wavelengths. The estimated radiative transition parameters are tabulated. The effective vibrational temperature of Swan band system of C₂ molecule is found agreed with the effective rotational temperature from photosphere spectrum. Hence, the radiative transition parameters and effective temperatures help us to ascertain the presence of C₂ molecule in the interstellar medium, photosphere and sunspots.     

Spatial Distribution and Temporal Evolution of Coronal Bright Points

Solar Physics - We present a statistical study of the spatial distribution and temporal evolution of coronal bright points (BPs) by analyzing a continuous set of observations of a quiet-Sun region...     

γ射线暴谱硬度比的时间演化特征

采用小波分析方法对康普顿γ射线天文台(CGRO)上的BATSE仪器观测到的γ暴光变曲线数据进行去噪处理,并提出时间分辨的谱硬度比定义,用包含有599个暴的样本研究谱硬度比随时间的演化规律,结果表明:(1)样本中77%暴的谱硬度比随时间按"硬到软"规律演化,而23%暴谱硬度比随时间按"软到硬"规律演化,尤其是3%暴在整个暴中呈现单调的"软到硬"趋势。(2)平均谱硬度比随时间单调地以"硬到软"规律演化。(3)持续时间不同的暴,其谱硬度比演化曲线有较大的差异,其中"硬到软"演化趋势最显著的是持续时间在23～35s之间的那些暴;持续时间在1～10s的暴的演化特征跟其它组差异最显著,呈现比较明显的"软到硬"演化规律;持续时间在35～53s之间的暴平均谱硬度比几乎没有随时间演化。(4)不同辐射强度的暴平均谱硬度比的演化特征不同,随着峰值流量的增大,谱硬度比演化由"硬-软-硬"逐渐转变为"软-硬-软":峰值流量越大,"软-硬-软"的趋势越显著,而峰值流量越小,其峰值流量"硬-软-硬"的趋势越显著。我们对这些结果进行了简单的讨论。     

Umbral boundaries,convection, and the depth of sunspots

The boundary between the umbra and penumbra of a sunspot is consistently observed to be very sharp, on the order of 500 km. Approximating the sunspot as a static region in a homogeneous medium with a radiative surface, temperature distributions resulting from a variety of convective motions exterior to the sunspot are calculated. The calculations suggest that, for the exterior convection to produce the observed boundary, the maximum depth of the region of inhibited convection below a sunspot umbra is on the order of 10³ km.     

Identification of AlF Molecular Lines in Sunspot Umbral Spectra

High resolution FTS sunspot umbral spectra from NSO/Kitt Peak were used to detect rotational lines due to 11 electronic transitions of the molecule AlF, in the wavelength region 4400 – 9000 Å. The presence of lines due to bands C – A (0,0), (0,1), (0,2) and (1,2), D – A (0,0) and (0,1), F – A (0,0), G – A (0,0), and F – B (0,0) is confirmed. Further, the presence of lines due to C – A (1,0) and (1,1) transitions is treated as doubtful because of heavy blending in the region, by rotational lines of TiO. Among the identified lines, those which are well resolved were selected for measurement of equivalent widths. The measured values for the bands D – A (0,0) and F – A (0,0) were used to estimate the respective effective rotational temperatures to be 1240 ± 120 K and 2390 ± 400 K.