AR5395:精细结构,磁剪切和耀斑

用26cm太阳望远镜的高分辨光球色球照片和北京夭文台怀柔站的太阳磁图证认出AR5395活动区中5段剪切的磁极性反转线(中性线)。考察这些线段与黑子精细结构,活动区暗条以及耀斑活动之间的关系。结果表明,多数观测到的耀斑发生在磁剪切     

太阳的磁绳暗条和一个Ⅲb级耀斑

2000年9月14－18日在紫金山天文台赣榆观测站观测到太阳上有一个中小型活动区，黑子面积不大，但有一个奇特的活动区暗条，16日产生了一个Ⅲb级耀斑，有较强的地球物理效应。计算该区的磁结构，结果发现此磁绳状暗条与磁中性线附近低磁弧系相关，磁场在磁绳附近有强剪切，QSL分析显示三维磁重联能够在暗条附近出现，这可解释大耀斑的形成。     

1989年7月5日耀斑活动区的磁场特征

本文详细分析了1989年7月5日有连续发射的耀斑对应的活动区磁场。得出:磁场强度和黑子面积分布都有“前导大后随小”的特征;两异极黑子挤压位置的中性线呈“V”形;产生连续发射的四个耀斑核,除一个位于宁静背景上外,其余三个均位于中性线两侧;连续发射最明显的B点耀斑核位于磁剪切和磁挤压的交点以及磁场梯度最大(0.52高斯公里~(-1))的位置上。     

1984年2月25日日面大耀斑光学特性

1984年2月25日,日面爆发了一个高能大耀斑。我们取得了该耀斑过程的光球黑子活动区强磁场以及黑子、H_α色球等光学资料。分析表明:1.这种高能大耀斑是产生在有黑子剪切运动、新浮磁流和磁场梯度大的磁中性线(H_n=0)两侧;2.耀斑发展到极大前后,不但会掩盖部分后随黑子半影,而且还会进一步掩盖这些后随黑子本影;3.在高能大耀斑爆发过程中,相应的光球黑子活动区的强磁场会出现变化,磁通量增长率为1.0×10~8韦伯/秒,磁场梯度最大为0.2高斯/公里;4.黑子间的相对运动速度最大可达0.3公里/秒。     

太阳耀斑的一种发电机机制的设想

当太阳黑子磁环从太阳对流层深层上浮到太阳表面时,便形成了一个双极黑子群的活动区。在活动区内,纵向磁场为零的中性线区域为高压区,垂直向上气流把黑子磁弧吹入日冕。同时在磁弧的顶部,即在中性线上空产生了感应电流,它的焦耳耗散形成了H_α耀斑。然而,因两个黑子区内为低压区,吸注气流从黑子磁弧的两条腿部顺磁力线流向黑子,它与位于中性线的上升气流形成了两个对称环流,随着环流和磁弧的发展,耀斑区向中性线两旁分离,因而呈现出双带耀斑的特征。本文还估计了耀斑的能量,只要横越磁场的速度,v_⊥～0.3—3公里。秒~(-1),磁场强度B～10—100高斯,这就足以产生耀斑所需要的10~(29)～10~(33)尔格的能量。     

质子耀斑活动区特征与无力磁场

本文在综合分析质子耀斑活动区观测特点的基础上,指出在密集的多极黑子构成的局部区域中,同极黑子分裂,互相排斥,异极黑子相互靠近,向异极区中场强较弱部分的挤压和渗入,是一大批质子耀斑活动区的共同特点.这种黑子间的相对运动,使中性线严重扭曲,呈现出质子耀斑活动区特有的“S”型。根据这些观测特点,寻找到了一种定量估计无力因子的方法。对三个典型的质子耀斑活动区估计了无力因子的变化,并在常无力因子的假定下进行了无力场结构和势场磁能的计算。计算表明质子耀斑发生前无力因子逐渐增加,而势场磁能逐渐减小,减少的势场能量可能正是无力场得到发展的能源,足够质子耀斑的需要。     

22周强质子耀斑活动区的特征

本文研究了22周中的9个强质子耀斑活动区的共同特征,研究结果表明:单个团状结构黑子,即众多异极性黑子本影核紧锁在同一半影结构中的δ型黑子是强质子耀斑活动区的典型形态特征。黑子群的旋转是质子耀斑活动区的又一重要特征,黑子群的旋转方向与日面南、北半球无关。强质子耀斑的爆发总是在黑子群旋转角度达到正或负相极大之后出现。质子耀斑后,磁绳的松弛,黑子群可能会出现反向旋转,强的剪切过程和质子耀斑可能会再度出现。     

AR5229活动区中耀斑和磁场的关系(英文)

本文研究了活动区5229中的H_β耀斑和磁场的关系。所用资料为北京天文台怀柔太阳观测站1988年11月13—18日期间获得的(时值活动区5229位于E40°W40°)。按活动区磁场演化情况,考察了新浮现磁流、磁剪切和磁对消与耀斑形成的关系。 图1a-1f给出了怀柔站观测到的11个H_β耀斑及87个耀斑核在纵向磁图上的情况。磁图以等高斯线形式给出,图中虚线表示负极,实线表示正极,等高斯线由外向内分别为20,40,80,160,320,640,960,1280,1600,1920,2240,2580,2800高斯。黑色小块表示Hβ耀斑核。其中有四分之三的Hβ耀斑核离开极性反变线的距离在10弧秒之内。发生在该活动区的耀斑超过80个,而怀柔站观测的仅是很小一部分。这对于耀斑建立过程的研究是很不够的,必需补充其他天文台的资料。注意到周报上已列出该活动区的软X射线(1～8A)M1.0级以上的高能耀斑事件,将它们补充进图1,用黑色三角形表示,画其位置时考虑到耀斑、黑子及磁特征之间的关系和它们彼此之间的时间差,并按Howard和Harvey给出的较差自转公式进行了改正。10个高能耀斑事件中有6个可能与磁特征N_3,N_7和P_2的衰减(即对消,另一极性在复杂活动区中衰减不明显)有关;另外的事件可能与发生在磁特征N_2、P_2之间的磁剪切有关。     

X级耀斑过程中的磁剪切变化(英文)

通过对活动区NOAA 6891中三个X级耀斑前后的向量磁场分析 ,研究耀斑发生条件与耀斑发生前后横向磁场和磁剪切变化的关系。我们发现与Hagyard的耀斑发生条件不同的是 ,强的横向磁场和磁剪切不是活动区中耀斑发生的充要条件。我们的结果表明 ,活动区NOAA 6891 1 991年 30日的耀斑发生在横向磁场和磁剪切剧烈下降后。尽管 1 0月 2 7日的耀斑发生后横向磁场和磁剪切变化很大 ,但由于有新磁流浮现 ,造成磁中性线的改变 ,使得横向磁场和磁剪切变化与耀斑发生的联系变得比较复杂。     

太阳黑子运动引起的耀斑与活动区的耦合

利用紫台赣榆站太阳精细结构望远镜拍摄的色球和光球照片，研究了1990年11月6日至13日NOAA6361活动区的磁位形演化和耀斑产生区域，发现该活动区的活动主要集中在11日和12日两天还观测到新老活动区的碰撞耦合及耦合界面处小纤维（fibril）的快速变化，这些现象是由于前导黑子之一的p1黑子的连续几天的运动造成的．所有的活动也主要集中在P1黑子的周围．     

Instructions for authors

正Research in Astronomy and Astrophysics publishes original research papers and reviews 011 all liranchcs of astronoiriy and astrophysics.Reviews arc by invitation only.Important new results that require rapid publication can be submitted as a Letter(Letters must be restricted in length     

A thermodynamic model of high temperature lava vaporization on Io

We modified the MAGMA chemical equilibrium code developed by Fegley and Cameron (1987, Earth Planet. Sci. Lett. 82, 207-222) and used it to model vaporization of high temperature silicate lavas on Io. The MAGMA code computes chemical equilibria in a melt, between melt and its equilibrium vapor, and in the gas phase. The good agreement of MAGMA code results with experimental data and with other computer codes is demonstrated. The temperature-dependent pressure and composition of vapor in equilibrium with lava is calculated from 1700 to 2400 K for 109 different silicate lavas in the ONaKFeSiMgCaAlTi system. Results for five lavas (tholeiitic basalt, alkali basalt, Barberton komatiite, dunite, and a molten type B1 Ca, Al-rich inclusion) are discussed in detail. The effects of continuous fractional vaporization on chemistry of these lavas and their equilibrium vapor are presented. The predicted abundances (relative to Na) of K, Fe, Si, Al, Ca, and Ti in the vapor equilibrated with lavas at 1900 K are lower than published upper limits for Io's atmosphere (which do not include Mg). We predict evaporative loss of alkalis, Fe, and Si during volcanic eruptions. Sodium is more volatile than K, and the Na/K ratio in the gas is decreased by fractional vaporization. This process can match Io's atmospheric Na/K ratio of 10±3 reported by Brown (2001, Icarus 151, 190-195). Silicon monoxide is an abundant species in the vapor above lavas. Spectroscopic searches are recommended for SiO at IR and mm wavelengths. Reactions of metallic vapors with S- and Cl-bearing volcanic gases may form other unusual gases including MgCl₂, MgS, MgCl, FeCl₂, FeS, FeCl, and SiS.     

Instructions for authors

正Research in Astronomy and Astrophysics publishes original research papers and reviews on all branches of astronomy and astrophysics.Reviews are by invitation only.Important new results that require rapid publication can be submitted as a Letter(Letters must be restricted in length to 6 printed pages).Authors who submit a paper are expected to be able to certify that the paper is original work,     

Alkali and halogen chemistry in volcanic gases on Io

We use chemical equilibrium calculations to model the speciation of alkalis and halogens in volcanic gases emitted on Io. The calculations cover wide temperature (500-2000 K) and pressure (10⁻⁶ to 10⁺¹ bars) ranges, which overlap the nominal conditions at Pele (T=1760 K, P=0.01 bars). About 230 compounds of 11 elements (O, S, Li, Na, K, Rb, Cs, F, Cl, Br, I) are considered. The elemental abundances for O, S, Na, K, and Cl are based upon observations. CI chondritic elemental abundances relative to sulfur are used for the other alkalis and halogens (as yet unobserved on Io). We predict the major alkali species in Pele-like volcanic gases and the percentage distribution of each alkali are LiCl (73%), LiF (27%); NaCl (81%), Na (16%), NaF (3%); KCl (91%), K (5%), KF (4%); RbCl (93%), Rb (4%), RbF (3%); CsCl (92%), CsF (6%), Cs (2%). Likewise the major halogen species and the percentage distribution of each halogen are NaF (88%), KF (10%), LiF (2%); NaCl (89%), KCl (11%); NaBr (89%), KBr (10%), Br (1%); NaI (61%), I (30%), KI (9%). We predict the major halogen condensates and their condensation temperatures at P=0.01 bar are NaF (1115 K), LiF (970 K); NaCl (1050 K), KCl (950 K); KBr (750 K), RbBr (730 K), CsBr (645 K); and solid I₂ (200 K). We also model disequilibrium chemistry of the alkalis and halogens in the volcanic plume. Based on this work and our prior modeling for Na, K, and Cl in a volcanic plume, we predict the major loss processes for the alkali halide gases are photolysis and/or condensation onto grains. Their estimated photochemical lifetimes range from a few minutes for alkali iodides to a few hours for alkali fluorides. Condensation is apparently the only loss process for elemental iodine. On the basis of elemental abundances and photochemical lifetimes, we recommend searching for gaseous KCl, NaF, LiF, LiCl, RbF, RbCl, CsF, and CsCl around volcanic vents during eruptions. Based on abundance considerations and observations of brown dwarfs we also recommend a search of Io's extended atmosphere and the Io plasma torus for neutral and ionized Li, Cs, Rb, and F.     

The climatic and physiographic controls of the eastern Mediterranean over the late Pleistocene climates in the southern Levant and its neighboring deserts

Modern-day synoptic-scale eastern Mediterranean climatology provides a useful context to synthesize the diverse late Pleistocene (60–12 ka) paleohydrologic and paleoenvironmental indicators of past climatic conditions in the Levant and the deserts to its south and east. We first critically evaluate, extract, and summarize paleoenvironmental and paleohydrologic records. Then, we propose a framework of eastern Mediterranean atmospheric circulation features interacting with the morphology and location of the southeast Mediterranean coast. Together they strongly control the spatial distribution of rainfall and wind pattern. This cyclone–physiography interaction enforces the observed rainfall patterns by hampering rainfall generation south and southeast of the latitude of the north Sinai coast, currently at 31°15′.The proposed framework explains the much-increased rains in Lebanon and northern Israel and Jordan as deduced from pollen, rise and maintenance of Lake Lisan, and speleothem formation in areas currently arid and semiarid. The proposed framework also accounts for the southward and eastward transition into semiarid, arid, and hyperarid deserts as expressed in thick loess accumulation at the deserts' margins, dune migration from west to east in the Sinai and the western Negev, and the formation of hyperarid (< 80 mm yr^− 1) gypsic–salic soils in the southern Negev and Sinai. Our climatic synthesis explains the hyperarid condition in the southern Negev, located only 200–250 km south of the much-increased rains in the north, probably reflecting a steeper rainfall gradient than the present-day gradient from the wetter Levant into its bordering southern and eastern deserts.At present, the rainiest winter seasons in Lebanon and northern and central Israel are associated with more frequent (+ 20%), deeper Cyprus Lows traversing the eastern Mediterranean at approximately the latitude of southern Turkey. Even these wettest years in northern Israel do not yield above average annual rainfall amounts in the hyperarid southern Negev. This region is mainly influenced by the Active Red Sea Troughs that produce only localized rains. The eastern Mediterranean Cyprus Lows also produce more dust storms and transport higher amounts of suspended dust to the loess area than any other atmospheric pattern. Concurrent rainfall and dust are essential to the late Pleistocene formation of the elongated thick loess zone along the desert northern margin. Even with existing dust storms, the lack of rain and very sparse vegetation account for the absence of late Pleistocene loess sequences from the southern Negev and the formation of hyperarid soils.When the north Sinai coast shifted 30–70 km northwest due to last glacial global sea level lowering, the newly exposed coastal areas supplied the sand and dust to these active eastern Mediterranean cyclones. This enforced the latitude of the northern boundary of the loess zone to be directly due east of the LGM shoreline. This shift of coast to the northwest inhibited rainfall in the southern Levant deserts and maintained their hyperaridity. Concurrently, frequent deep eastern Mediterranean Cyprus Lows were funneled along the northern Mediterranean increasing (probably doubling) the rains in central and northern Israel, Lebanon, southwestern Syria and northern Jordan. These storms and rains formed lakes, forests, and speleothems only a short distance north of the deserts in the southern Levant.     

Active hot star shells

Interferometry in the visible provides milliarcsecond spatial resolution and thus has been used for studying the circumstellar environment of active hot stars. In this paper I will illustrate how the visibility modulus and phase can be used to better constrain the physics of Be disks through results from the VLA, the MkII and the GI2T interferometers. I will insist on the importance and the potential of coupling high angular resolution with high spectral resolution to the study of Be shells. Finally I will present a possible study of the circumstellar disk of Be stars using the VLTI. This revised version was published online in July 2006 with corrections to the Cover Date.     

Fitting X-ray Afterglow Light curves of Gamma-ray Bursts by Using the Magnetar Energy Injection Model

The central compact object for some gamma-ray bursts (GRBs) may be a strongly magnetized millisecond pulsar. It can inject energy to the outer shock of the GRB by through the magnetic dipole radiation, and therefore causes the shallow decay of the early afterglow. Recently, from a large number of GRB X-ray afterglows observed by Swift/XRT(X-ray telescope), it is revealed that many of them exhibit the shallow decay about 10²∼10⁴ s after the burst prompt emission. We have fitted the X-ray afterglow light curves of 11 GRBs by using the energy injection model of a magnetar with the rotation period in the millisecond order of magnitude. The obtained result shows the validity and universality of the magnetar energy injection model in explaining the shallow decay of afterglows, and simultaneously provides some constraints on the magnetic field strength and rotation period of the central magnetar.     

Natural superrotation of a rarefied planetary atmosphere

We consider the kinetics of a rarefied rotating planetary atmosphere. The spatial distributions of the atmospheric-gas density and mean angular velocity were determined by analyzing the exact solution of the two-dimensional kinetic equation. We show that the angular velocity of the gas at some distance from the planet could be higher than that in the initial layer starting from which the atmosphere is rarefied. Our model calculations elucidate the superrotation mechanism under consideration.