视超光速射电节点的频谱演化：持续供能的喷流—激波模型

本提出一个持续供能的喷流－激波模型来解释视超光速射电节点频谱演化的普遍特性。理论计算指出，射电爆发频谱的反转频率Ｖｍ和频谱极大流量Ｓｍ之间的关系具有典型的３阶段演化方式，并且与类星体３Ｃ３４５中观测到的视超光速节点Ｃ４的演化行为相当好地符合。令Ｓｍ∝Ｖｍ＾ζ，则在上升阶段ζ〈￣－３；在平坦变化阶段ζ≈０，而在衰减阶段ζ≈１，爆发幅度和流量极大的迟后时间对频率的关系ΔＳｍａｘ（Ｖ）和Δｔ（Ｖ），都     

Blazar天体射电爆发的持续注入喷流模型

为了解释Blazar天体射电爆发的普遍演化特性，本文提出一个持续注入的喷流模型．假定在喷流基底上以相对论性速度持续地注入相对记等离子体（由磁场和相对论电子组成）．这一等离子体在沿喷流向外运动时经受绝热膨胀损耗．理论计算表明，射电爆发的频谱演化具有Valtaoja等人所建议的典型的3阶段演化形式.它们非常好地重现了Blazar天体中观测到的射电爆发的普遍行为．     

Blazar喷流节点运动视速度的统计研究

VLBI观测表明,TeV伽马射线Blazar(耀变体)的喷流运动视速度远小于MeV/GeV伽马射线Blazar,然而TeV伽马射线辐射流量的快速变化却要求这些Blazar的相对论喷流速度与MeV/GeV Blazar的相当.对于这一矛盾,目前有多种解释.为了检验这些模型,我们收集了VLBI对Blazar喷流运动的监测数据,样本包括86个FSRQs(平谱射电类星体)、22个BL Lac天体,共108个Blazar;从统计上研究了,该样本中各Blazar最大视速度喷流节点的位置与射电光度相关关系.结果表明,Blazar最大视速度喷流节点的位置与射电光度有较强的相关关系,随着Blazar射电光度的减小,喷流中最大视速度VLBI节点的位置到VLBI核的距离逐渐变小.这意味着,TeV伽马源(低光度Blazar)的喷流减速区距离VLBI核较近,喷流从高能辐射区到VLBI可分辨尺度已经减速,支持减速喷流模型对TeV伽马射线Blazar上述矛盾的解释.     

Blazar天体中光学射电大爆发的频谱演化

本文讨论Ｂｌａｚａｒ天体中光学射电大爆发频谱演化的理论模型．考虑沿喷流传播的相对论性激波所注入或加速的相对论性电子，受到康普顿、同步辐射和绝热膨胀三种损耗，并计及相对论电子能谱的高能截断．假定喷流轴线与观测者方向构成很小角度．文中给出了大爆发频谱三阶段连续演化的特性，即康普顿阶段，同步辐射阶段和绝热膨胀阶段的爆发特性．频谱演化用（Ｓｍ－ｖｍ）关系表达（见图２，图中Ｓｍ为频谱反转流量，ｖｍ为反转频率），它与一些Ｂｌａｚａｒ天体中观测到的典型形式相符合．     

Blazar天体射电爆发的持续注入喷流模型

为了解释Ｂｌａｚａｒ天体射电爆发的普遍演化特性，本提出一个持续注入的喷流模型。假定在喷流基底上以相对论性速度持续地注入相对论等离子体（由磁场和相对论电子组成）。这一等离子体在沿喷流向外运动时经受绝热膨胀损耗。理论计算表明，射电爆发的频谱演化具有Ｖａｌｔａｏｊａ等人所建议的典型的３阶段演化形式。它们非常好地重现了Ｂｌａｚａｒ天体中观测到的射电爆发的普遍行为。     

相对论电子的物理效应及其在高能天体中的应用

本文对相对论电子的辐射性质、能谱演化和加速机制等进行了简要的介绍。同时，对相对论电子在高能天体中的辐射作用和特性进行了简要的综述。本文给出了相对论电子在Blazar天体的射电辐射机制、光变机制、BL Lac天体的辐射机制以及γ暴的辐射机制等方面的应用研究成果。1、提出了相对论电子的光学薄同步辐射模型：解释Blazar天体的射电平谱：Blazar中心体的剧烈活动，使射电辐射区处于等离子体湍动状态，其中的相对论电子在湍动等离子体波的二交费米加速、激波加速、辐射损失、粒子逃逸和辐射区的绝热减速等物理过程作用下，形成较平的能谱，产生射电平谱。2、提出了新的Blazar天体光变模型：当Blazar天体爆发时，中心天体产生大量的相对论电子，注入喷流中；相对论电子产生同步辐射，并不断损失能量和逃逸辐射区，使它们的能谱快速变化，引起辐射发生快速光变。3、给出了BL Lac天体的等离子体反应堆模型：大量相对论电子从中心天体注入周围的等离子体反应堆中，通过同步辐射快速损失能量，同时这些电子同步吸收反应堆中不透明的光子，产生一个稳定、各向同性的幂律分布，其谱指数为γ＝3；然后，这些相对论电子通过等离子体反应堆的爆发或其表面扩散过程逃逸出来，辐射低频的同步辐射。模型解释了BL Lac天体的高频辐射表现出快速的谱变化性质，即流量减小时谱变陡。4、提出了相对论电子的内激波加速模型，解释γ暴的尖峰光变特性：在γ暴产生的相对论运动的壳层中，有内激波产生；激波在壳层中传播，耗散壳层的运动能，使其中的部分电子加速成为相对论电子。然后，这些电子通过同步辐射产生观测到的γ辐射。模型认为，γ暴中的每个尖峰辐射是一对内激波加速相对论电子的辐射过程，复杂的γ暴光变曲线是多对内激波辐射过程的叠加。     

激变射电源中偏振角快速旋转的解释

在许多激变射电源(Blazar天体)中,观测到一种非常特别的现象,即偏振角的快速旋转.在相对论喷流的框架下,这种偏振角的旋转可以用双成分模型来解释.在这个模型中,一个成分是作为背景喷流本身的辐射,是恒定不变的成分;另一个成分被认为是沿喷流传播的相对论性激波,它产生变化的流量和偏振.这两个成分的偏系辐射的叠加可以产生观测到的偏振角旋转。本文讨论了三个激变射电源(BL Lac,AO0235+164,0727-115)中发生的偏振角旋转.结果表明,用相对论喷流-激波双成分模型可以很好地拟合观测到的偏振角旋转、偏振度和流量变化。说明射电激变源中出现的快速偏振和流量变化可能是由于相对论激波沿喷流传播时,激波辐射区中磁场取向和有序性以及强度和电子密度的变化所引起的。     

M 87大尺度喷流的多波段研究

射电星系M87的大尺度喷流在射电、光学和X波段都已经具备高分辨率的成像观测和频谱观测。其各个节点的宽波段连续谱目前被认为是同步辐射主导的。文章采用相对论性电子同步辐射的Kardashev-Pacholczyk模型,对各节点的多波段连续谱进行了独立的最佳拟和,从而得到相应的多普勒因子。此外进一步结合各节点的视超光速运动的观测数据,导出了不同节点整体运动的Lorentz因子和对观测者的视角。计算结果表明,M87的大尺度喷流具有一定程度的弯曲,其整体动力学行为是减速的。     

6颗Blazar天体的长期光变和色指数变化

文中对6颗Blazar天体15年间的大量准同时性观测数据进行了处理分析,获得了长期的光变曲线和色指数变化曲线。对比分析光变曲线和色指数变化曲线,对色指数和亮度做相关分析,得出Blazar天体的光变包括长期的单色光变和有颜色变化的短期爆发两种成份,由光变的颜色差异我们提出引起Blazar天体光变的物理机制可能是几何效应调制的激波喷流模型。     

BLO 0716＋714射电和光学快速变化的相关性及其含义

本文讨论ＢＬＯ０７１６＋７１４中观测到的光学和射电快速变化（ＩＤＶ）的相关性及可能的解释。详细的分析表明，这种相关性有三个特点：（１）光学变化和５ＧＨｚ射电变化呈反相关，即光学极大和５ＧＨｚ射电极小相对应，反之亦然；（２）光学变化和射电频谱指数α＿５￣（８．３）的变化相关，具体他说，光学的增强和极大都与射电频谱反转频率向高频的位移有关；（３）光学和射电都有～１天的准周期变化，特别是射电频谱指数α８５·３的变化维持了大约７个准周期。上述相关的光学和射电快速变化可以在相对论喷流的框架下作出解释。作者提出，这类现象可能与激波在磁约束的准周期振荡的相对论喷流中的传播有关。     

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 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     

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.     

Born–Infeld type phantom model in the ω–ω′ plane

In this paper, we investigate the dynamics of Born–Infeld (B–I) phantom model in the ω–ω′ plane, which is defined by the equation of state parameter for the dark energy and its derivative with respect to N (the logarithm of the scale factor a). We find the scalar field equation of motion in ω–ω′ plane, and show mathematically the property of attractor solutions which correspond to ω _φ ∼−1, Ω _φ =1, which avoid the “Big rip” problem and meets the current observations well.      

A Comparison of Several Image Locating Algorithms in Astronomical Instruments

In astronomical observations at optical wavelengths, a fast image tracking system can be adopted to reduce the effects of the atmospheric seeing and telescopic tracking error, and therefore improve the observing efficiency. Aiming at the need of astronomical observations, totally 5 kinds of algorithms in two categories were selected to make a comparative study on their accuracies and stabilities under different noise conditions by both numerical experiment and laboratory test. The results indicate that the normalized cross-correlation method and barycenter method have not only a higher accuracy but also a better reliability against interferences, they will be applied to the high-resolution spectrograph of the Xinglong 2.16 m telescope and the scienti?c instruments of the SONG (Stellar Observations Network Group) project, respectively.     

Shear and vorticity in a combined Einstein-Cartan-Brans-Dicke inflationary lambda-Universe

A combined BCDE (Brans-Dicke and Einstein-Cartan) theory with lambda-term is developed through Raychaudhuri’s equation, for inflationary scenario. It involves a variable cosmological constant, which decreases with time, jointly with energy density, cosmic pressure, shear, vorticity, and Hubble’s parameter, while the scale factor, total spin and scalar field increase exponentially. The post-inflationary fluid resembles a perfect one, though total spin grows, but the angular speed does not (Astrophys. Space Sci. 312: 275, 2007d).      

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.