Photospheric and Chromospheric Oscillations in Solar Faculae

The differences between physical conditions in solar faculae and those in sunspots and quiet photosphere (increased temperature and different magnetic field topology) suggest that oscillation characteristics in facula areas may also have different properties. The analysis of 28 time series of simultaneous spectropolarimetric observations in facula photosphere (Fe?i 6569 Å, 8538 Å) and chromosphere (Hα, Ca?ii 8542 Å) yields the following results. The amplitude of five-minute oscillations of line-of-sight (LOS) velocity decreases by 20?–?40% in facula photosphere. There are only some cases revealing the inverse effect. The amplitude of four- to five-minute LOS velocity oscillations increases significantly in the chromosphere above faculae, and power spectra fairly often show pronounced peaks in a frequency range of 1.3?–?2.5 mHz. Evidence of propagating oscillations can be seen from space?–?time diagrams. We have found oscillations of the longitudinal magnetic field (1.5?–?2 mHz and 5.2 mHz) inside faculae.     

Application of Non-linear Analysis to Intensity Oscillations of the Chromospheric Bright Points

We have applied several nonlinear techniques to the intensity oscillations of the chromospheric bright points observed at the Vacuum Tower Telescope (VTT) of the Sacramento Peak Observatory. A 35-min time sequence obtained in the Caii H line over a quiet region at the center of the solar disk under high spatial, spectral, and temporal resolution has been used. A relatively new approach is used to detect the hidden periodicity and to extract the associated periodic component(s) from an apparently irregular time series. The unique feature of this approach is that the constituent component(s) can be non-sinusoidal in nature. The periodicity analysis shows that time series of intensity oscillations of most of the bright points can be composed of two non-sinusoidal periodic components with periodicity varying between 2.4 min and 5.8 min. With the help of a multivariate embedding technique, globally significant spatial nonlinear correlation is found. The identification of the nonlinear interaction between bright points is performed by using the methods of dynamical phase synchronization and the similarity index. The analysis indicates that bright points are interconnected in the sense that some bright points are more active and can influence the other relatively passive bright points.     

Chromospheric Internetwork Oscillations at Various Locations of the Quiet Sun

We analyze oscillation behaviours in chromospheric internetwork regions using spectral observations of the CⅡ1334 A line obtained with the Solar Ultraviolet Measurements of Emitted Radiation spectrograph (SUMER) aboard Solar and Heliospheric Observatory (SOHO). Three areas, 26 ×120arcsec2 each, at the various latitudes from the disk center to the north polar coronal hole, were rastered with a cadence of about 40-60 s in the solar minimum year. We obtained the time evolution of two-dimensional (2D) line intensity, continuum and line core shift. The continuum and the line shift show -3 min chromospheric oscillations in the internetwork regions underlying the coronal hole as well as at the disk center. We find that the CⅡ1334A line shift oscillates with an average speed of -1.7 km s-1, independent of the latitude, while its coherent scale decreases with latitude. On the other hand, the oscillation amplitude of the continuum around the 1334 A and the phase delay between the Doppler shift and continuum sli     

Oscillations in Solar Faculae. III. The Phase Relations Between Chromospheric and Photospheric Line-of-Sight Velocities

An analysis of line-of-sight velocity oscillation in nine solar faculae was undertaken with the aim of studying phase relations between chromospheric (He?i 10830?Å line) and photospheric (Si?i 10827 Å line) five-minute oscillations. We found that the time lag of the chromospheric signal relative to photospheric one varies from ?12 to 100 seconds and is about 50 seconds on average. We assume that the small observed lag can have three possible explanations: i) convergence of formation levels of He?i 10830?Å and Si?i 10827?Å in faculae; ii) significant increase of five-minute oscillation propagation velocity above faculae; iii) simultaneous presence of standing and travelling waves.     

Observations of Ions in Comets: A Contribution Towards Understanding the Comet-Solar Wind Interaction

Since many years cometary ions have been observed by the authors and their coworkers in order to study the comet-solar wind interaction. Comets with water production rates ranging from 10²⁸(46P/Wirtanen) to 6 10³⁰molecules s⁻¹(C/1995 O1 Hale-Bopp) have been observed. In this paper we briefly introduce the physics of the comet-solar wind interaction. New observations of comet C/1996 Q1 (Tabur) are presented, where for the first time H₂O⁺and CO⁺ions have been recorded exactly simultaneously with a two-channel system. They are compared with previous observations of comets C/1989 X1 (Austin), 46P (Wirtanen) and 109P (Swift-Tuttle). We use a new method of Wegmann et al. (1998), based on the MHD scaling law, to determine the water production of comet Tabur from its H₂O⁺column density map and obtain a value of 3.3 10²⁸water molecules s⁻¹. Nonstationary phenomena like tail rays and so-called tail disconnections are very briefly reviewed. A movie of plasma envelopes observed in the light of OH⁺in comet 1995 O1 (Hale-Bopp) is presented on the attached CD-ROM. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the Geometrical Properties of the Chromospheric Network

A sequence of Ca-K images obtained in a period of minimum solar activity, from July to November 1996, at the Rome Observatory with the PSPT (Precision Solar Photometric Telescope) prototype instrument have been used to analyze the geometrical properties of cells identified by the chromospheric network. In particular, we used 256 × 256 sub-arrays of the calibrated full-disk PSPT images. These sub-arrays, centered on the solar disk, are reduced to two-levels (binary) images by means of a suitable threshold after an FFT high-pass filtering. A medial axis transform, better known as skeleton, combined with a cellular automaton, is applied to the two-level images, in order to derive the cell boundaries. The regions corresponding to the cells are then filled by a growing algorithm. In this way we can derive a set of output parameters describing the cells geometry. The size distribution of the identified cells shows a continuous increase toward the smaller scales, rather than a small dispersion around a characteristic scale. Nevertheless the analysis of the inter-cell distances and of the area distribution pointed out a characteristic scale (square root of the area) of ± 24 Mm. To describe the cells irregularity and to probe the nature of solar turbulence, we apply a Mandelbrot fractal analysis to such irregularly shaped features. Examining the cell perimeter–area relationship we found the existence of a critical area at which a change in the geometrical properties occurs. This area corresponds to the scale of ± 24 Mm. The estimated fractal dimension for cells with area greater than the critical one is 1.35. This value, close to that predicted for isobars in the Kolmogorov 3-D turbulent theory, does not exclude a turbulent origin for such cells. The analysis seems to point to a common origin for solar granulation and supergranulation.     

太阳耀斑色球蒸发现象的研究进展

色球蒸发是耀斑能量释放后所导致的一种动力学现象,耀斑发生时,太阳大气被加热,形成的高压驱动等离子体物质向上运动,在观测上表现为高温谱线的多普勒蓝移,有时出现硬X射线足点源逐渐向环顶源的并合过程.数值模拟在理论上验证了色球蒸发理论.色球蒸发的加热机制主要包括热传导和非热粒子束加热.回顾了色球蒸发的研究进展,介绍了不同时期空间仪器对色球蒸发的观测结果,以及数值模拟方面的研究进展,并概括了目前存在的一些主要问题,最后给出简     

Chromospheric and coronal heating due to the dissipation of fast magnetoacoustic waves

The dissipation of ducted, fast, magnetoacoustic waves by ion viscosity and electron heat conduction in a radiating, optically thin atmosphere has been re-examined and the results compared with two previously published, conflicting sets of results. In general, the dissipation length of the waves increases with magnetic field strength and decreases with increase in density, and is a few wavelengths for waves of periods of several seconds in the active corona. Oscillations with such periods have been observed in the corona, so waves could, given the right conditions, be dissipated there, the energy so released being a contributory factor to coronal heating.     

The Origin of Sequential Chromospheric Brightenings

Sequential chromospheric brightenings (SCBs) are often observed in the immediate vicinity of erupting flares and are associated with coronal mass ejections. Since their initial discovery in 2005, there have been several subsequent investigations of SCBs. These studies have used differing detection and analysis techniques, making it difficult to compare results between studies. This work employs the automated detection algorithm of Kirk et al. (Solar Phys. 283, 97, 2013) to extract the physical characteristics of SCBs in 11 flares of varying size and intensity. We demonstrate that the magnetic substructure within the SCB appears to have a significantly smaller area than the corresponding \(\mbox{H}\upalpha\) emission. We conclude that SCBs originate in the lower corona around \(0.1~R_{\odot}\) above the photosphere, propagate away from the flare center at speeds of \(35\,\mbox{--}\,85~\mbox{km}\,\mbox{s}^{-1}\), and have peak photosphere magnetic intensities of \(148\pm2.9~\mbox{G}\). In light of these measurements, we infer SCBs to be distinctive chromospheric signatures of erupting coronal mass ejections.     

Variations of the Chromospheric Network with the Solar Cycle

We have digitized a small sample of Caii K spectroheliograms from the photographic archive of Arcetri Observatory for the period 1950–1970. For each digitized plate, active regions have been automatically identified and masked by applying an algorithm based on the geometrical connection between active pixels. Contrast histograms have been derived for the full disk and for quiet regions. Both of them show a neat Gaussian profile on the dark side and a significant tail on the bright side, due to the brightness enhancements associated with magnetic fields. A solar cycle dependence of the histogram asymmetry is clearly evident in quiet region data, thus confirming that the network component might provide a significant contribution to long-term variations of the total irradiance.     

Brightness and Blue-shift of Chromospheric Foot

A phenomenon of thebrightness and blue shift of chromospheric foot-points of coronal loops in per-flare phaseobserved by the Fine Structure Telescope of Yunnan Observatory,is reported in the presentarticle.The 4 foot-points of two coronal loops were confirmed by Yohkoh/HXT/SXTobservations.In the pre-flare phase,the separated point-shaped bright chromosphericplages,which are counterparts of the foot-points of the coronal loops on thechromosphre,show the blue-shift feature on off-band photons.The blue-shift feature of theplages indicates that there exists the pre-heat of material and upward flow of thematerial from the foot-points along the loops.The observations also reveal activation ofthe filament,which is located under the coronal loops.These observed results indicate thatmaterial “evaporation” occurs in the pre-flare phase,and violent variation of thechromospheric magnetic field probably is one of the reasons of causing chromosphereevaporation     

Evidence of Chromospheric Activity on HR 1099

We present an observational evidence of the chromospheric activity on HR1099. The IUE spectra of HR 1099 were used for the ultraviolet photometry and for the intensity variation of chromospheric emission line. Ultraviolet light curves were made from the low and high dispersion IUE spectra and were compared with a optical light curve. We have analyzed the ultraviolet and optical light curves by the Wilson and Devinney computing code including dark spots. The intensity variation of Mg II emission line depends on the orbital phase. The maximum intensity of Mg II emission line occurs at the phase of light minimum where dark spot visibility is maximum due to strong chromospheric activity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Chromospheric Activity of Weak-Lined T Tauri Stars

A summary of our ongoing high and medium resolution optical observational program, devoted to the study of chromospheric activity of pre-main sequence stars, is reported here. The study is centered in bona-fid weak-lined T Tauri stars (WTTS) in Taurus with known rotational period, and in WTTS recently discovered by the ROSAT All-Sky Survey. It is our purpose to quantify the phenomenology of the chromospheric activity of each star determining stellar surface fluxes in the more important chromospheric activity indicators (Ca II H & K, Hβ, Hα, Ca II IRT) as well as to obtain the Li I abundance, a better determination of the stellar parameters, spectral type, and possible binarity. By using these chromospheric excess emissions we will study the flux-flux and rotation-activity relationships in order to get insights into the mechanisms which drive solar-like stellar activity in this kind of low mass pre-main sequence stars. This revised version was published online in July 2006 with corrections to the Cover Date.     

Key Properties of Solar Chromospheric Line Formation Process

The distribution or wavelength-dependence of the formation regions of frequently used solar lines, Hα，Hβ，CaIIH and CaII8542,in quiet Sun,faint and bright flares is explored in the unpolarized case.We stress four aspects characterising the property of line formation process:1) width of line formation core;2) line formation region;3)influence of the temperature minimum region; and 4) wavelength ranges within which one can obtain pure chromospheric and photospheric filtergrams.It is shown that the above four aspects depend strongly on the atmospheric physical condition and the lines used. The formation regions of all the wavelength points within a line may be continuously distributed over one depth domain or discretely distributed because of no contribution coming from the temperature minimum region, an important domain in the solar atmosphere that determines the distribution pattern of escape photons. On the other hand, the formation region of one wavelength point may cover only one height range or spread over two domains which are separated again by the temperature minimum region. Different lines may form in different regions in the quiet Sun. However, these line formation regions become closer in solar flaring regions. Finally, though the stratification of line-of-sight velocity can alter the position of the line formation core within the line band and result in the asymmetry of the line formation core about the shifted line center, it can only lead to negligible changes in the line formation region or the line formation core width. All these results can be instructive to solar filtering observations.     

色球和日冕的MHD加热机制

扼要地介绍了色球和日冕加热问题的研究历史。随着空间太阳观测技术的进步，人们认识到色球和日冕加热机制主要与MHD过程有关。因此，在本文中着重介绍四种MHD色球和日冕加热机制：（1）阿尔芬波；（2）MHD湍动；（3）场向电流；（4）磁重联。由于这四种加热机制的有效性都需要通过高分辨率观测来判定，所以空间太阳观测对于研究色球和日冕加热问题具有重大意义。     

The Chromospheric Radiation on the Circumstellar Shell of Tx Piscium

Using the chromospheric UV flux based on IUE data, we have undertaken a wavelength calculation of the rates of photodissociation and the a abundances of the relevant molecules CO, SiS, HCN and C₂H₂ for the inner region of the circumstellar shell of the carbon-rich star TX Psc. Shielding by heavy elements and dust was taken into account. Further, for CO, the line self-shielding as an additional shielding process was included. We find that the large influence of the shielding prevents the molecules from photodissociation in the internal layer of the shell of TX Psc. The possibility of detecting C₂H₂ via the equivalent widths of the infrared lines in the circumstellar shell is discussed. Finally, we estimate the antenna temperature and the luminosity of the fine-structure lines of [CI]609µ and [CII]158µ of the envelope of TX Psc, respectively.     

2004年6月8日金星凌日Hα色球观测

介绍了2004年6月8日云南天文台全日面Hα色球望远镜观测金星凌日的情况，以及对太阳色球活动的监测，并直接给出不同时刻金星在太阳球面的投影和金星的实时图像资料。金星凌日时，Hα色球活动区均未发生耀斑爆发及其它伴随现象。整个凌日过程金星没有掩盖活动区。     

色球耀斑Hα谱线轮廓不对称性研究

Hα谱线轮廓的不对称性是色球耀斑光谱观测中的重要特征,也是耀斑动力学过程的重要观测事实之一．以紫金山天文台太阳光谱仪的观测资料为依据,给出Hα谱线不对称性的典型轮廓．在考虑氢原子非热激发、电离的作用下,经验性地计算了不同大气模型下谱线的不对称性特征,并在此基础上,对观测谱线进行半经验的研究．结果表明, 色球区的向下运动能够产生Hα谱线的红、蓝不对称性,并可以再生具体耀斑的谱线不对称性特征．此外,不仅非热粒子的能流、谱指数大小以及速度场所处的高度对谱线轮廓有影响,耀斑大气的背景模型对谱线的轮廓也有一定的影响．