Particle Acceleration in Relativistic Outflows

In this review we confront the current theoretical understanding of particle acceleration at relativistic outflows with recent observational results on various source classes thought to involve such outflows, e.g. gamma-ray bursts, active galactic nuclei, and pulsar wind nebulae. We highlight the possible contributions of these sources to ultra-high-energy cosmic rays.     

An Overview of Jets and Outflows in Stellar Mass Black Holes

In this article, we will briefly review the current empirical understanding of the relation between accretion state and outflows in accreting stellar mass black holes. The focus will be on the empirical connections between X-ray states and relativistic (‘radio’) jets, although we are now also able to draw accretion disc winds into the picture in a systematic way. We will furthermore consider the latest attempts to measure/order jet power, and to compare it to other (potentially) measurable quantities, most importantly black hole spin.     

Numerical 3-D time-dependent MHD model of the solar wind

A fully three-dimensional, time-dependent MHD model of the solar corona and the solar wind is developed. The proposed model is an upgrading of the steady-state model (Usmanov, 1993a,b). A numerical self-consistent solution for 3-D MHD equations is constructed for the region between the solar photosphere and 1.5 AU. The unique features of the proposed model are: (i) uniform coverage and self-consistent treatment of the regions of subsonic/sub-Alfvénic and supersonic/super-Alfvénic flows, (ii) as a background for transients, a steady-state solution for the ambient solar wind is used. The parameters of the initial pulses are prescribed in terms of the near-Sun shock velocities (as inferred from the metric Type II radio burst observations) relative to the preshock steady-state flow parameters.     

Towards a Unified View of Inhomogeneous Stellar Winds in Isolated Supergiant Stars and Supergiant High Mass X-Ray Binaries

Massive stars, at least \(\sim10\) times more massive than the Sun, have two key properties that make them the main drivers of evolution of star clusters, galaxies, and the Universe as a whole. On the one hand, the outer layers of massive stars are so hot that they produce most of the ionizing ultraviolet radiation of galaxies; in fact, the first massive stars helped to re-ionize the Universe after its Dark Ages. Another important property of massive stars are the strong stellar winds and outflows they produce. This mass loss, and finally the explosion of a massive star as a supernova or a gamma-ray burst, provide a significant input of mechanical and radiative energy into the interstellar space. These two properties together make massive stars one of the most important cosmic engines: they trigger the star formation and enrich the interstellar medium with heavy elements, that ultimately leads to formation of Earth-like rocky planets and the development of complex life. The study of massive star winds is thus a truly multidisciplinary field and has a wide impact on different areas of astronomy.In recent years observational and theoretical evidences have been growing that these winds are not smooth and homogeneous as previously assumed, but rather populated by dense “clumps”. The presence of these structures dramatically affects the mass loss rates derived from the study of stellar winds. Clump properties in isolated stars are nowadays inferred mostly through indirect methods (i.e., spectroscopic observations of line profiles in various wavelength regimes, and their analysis based on tailored, inhomogeneous wind models). The limited characterization of the clump physical properties (mass, size) obtained so far have led to large uncertainties in the mass loss rates from massive stars. Such uncertainties limit our understanding of the role of massive star winds in galactic and cosmic evolution.Supergiant high mass X-ray binaries (SgXBs) are among the brightest X-ray sources in the sky. A large number of them consist of a neutron star accreting from the wind of a massive companion and producing a powerful X-ray source. The characteristics of the stellar wind together with the complex interactions between the compact object and the donor star determine the observed X-ray output from all these systems. Consequently, the use of SgXBs for studies of massive stars is only possible when the physics of the stellar winds, the compact objects, and accretion mechanisms are combined together and confronted with observations.This detailed review summarises the current knowledge on the theory and observations of winds from massive stars, as well as on observations and accretion processes in wind-fed high mass X-ray binaries. The aim is to combine in the near future all available theoretical diagnostics and observational measurements to achieve a unified picture of massive star winds in isolated objects and in binary systems.     

Driving mechanisms for the solar wind

In this review, we consider the central physical aspects pertinent to the acceleration of the solar wind. Special importance is placed on the high-speed streams since the properties of these structures seem to strain the various theoretical explanations the most. Heavy emphasis is also given to the observations — particularly as to what constraints they place on the theories. We also discuss certain sporadic events such as spicules, macrospicules, X-ray bright points, and outflows seen in the EUV associated with the explosive events, jets, and coronal bullets which could be of relevance to this problem.Three theoretical concepts pertaining to the solar wind acceleration process are examined — purely thermal acceleration with and without extended heating, acceleration due to Alfvén wave pressure, and diamagnetic acceleration. Emphasis is given to how well these theories meet the constraints imposed by the observations. Diamagnetism is argued to be a powerful ingredient in solar wind theory, both in the light of observed sporatic outflows seen in the chromosphere and transition region and also because of its effectiveness in increasing the flow speed and producing strong acceleration near the Sun in line with coronal hole observations.     

矢通量分裂-TVD杂交新格式及其应用

在贴体曲线坐标系中,本文提出了一个高分辨率的新格式,它是Steger-Warming的矢通量分裂与Harten的TVD(Total Variation Diminishing)格式的杂交,用于计算跨音速定常流动和捕获激波。典型的跨音速内流和叶栅流的算例表明:在60×15网格下捕获的激波过渡区不超过两个网格,证明其分辨率较高;分析激波附近的数值结果,没出现“低亏、过跳”、伪振荡现象;与实验结果的比较表明,对定常流在无人为附加耗散项的条件下它能给出较高质量无数值波动的激波流场解。     

The Calculation of Frequency-Modulation Distortion in Linear Networks

A numerical method is developed for the calculation of steady-state FM distortion in a linear passive network from the character of the FM signal input and the steady-state transfer characteristics of the network. The method of calculating FM distortion requires the solution of a finite set of linear equations which is accomplished readily by a digital computer. To illustrate the use of the method, the FM distortion introduced by a Chebyshev-response bandpass filter is calculated for a range of network and input signal parameters.     

Numerical simulation of a boiling up fluid flow in the variable cross-section channels

A physical and mathematical model of a boiling-up fluid flow in the variable crosssection channels is proposed. The numerical model is based on the solution of the Navier-Stokes nonstationary equations for compressible fluid by the implicit finite-difference method. We present the results of the numerical modeling for two-phase flow characteristics at the initial stage of the evaporation process and the steady-state quasistationary flow of a two-phase medium.     

Presolar Grains in Meteorites and Their Compositions

Small amounts of pre-solar “stardust” grains have survived in the matrices of primitive meteorites and interplanetary dust particles. These grains—formed directly in the outflows of or from the ejecta of stars—include thermally and chemically refractory carbon materials such as diamond, graphite and silicon carbide; as well as refractory oxides and nitrides. Pre-solar silicates, which have only recently been identified, are the most abundant type except for possibly diamond. The detailed study with modern analytical tools, of isotopic signatures in particular, provides highly accurate and detailed information with regard to stellar nucleosynthesis and grain formation in stellar atmospheres. Important stellar sources are Red Giant (RG) and Asymptotic Giant Branch (AGB) stars, with supernova contributions apparently small. The survival of those grains puts constraints on conditions they were exposed to in the interstellar medium and in the early solar system.     

Protostellar Winds and Chondritic Meteorites

We discuss the interaction between the magnetosphere of a young star and its surrounding accretion disk. We consider how an X-wind can be driven magnetocentrifugally from the inner edge of the disk where accreting gas is diverted onto stellar field lines either to flow onto the Sun or to be flung outwards with the wind. The X-wind satisfies many observational tests concerning optical jets, Herbig-Haro objects, and molecular outflows. Connections may exist between primitive solar system materials and X-winds. Chondrules and calcium-aluminum-rich inclusions (CAIs) experienced short melting events uncharacteristic of the asteroid belt where meteorites originate. The inner edge of the solar nebula has the shortest orbital timescale available to the system, a few days. Protosolar flares introduce another timescale, tens of minutes to hours. CAIs may form when solids are lifted from shaded portions of the disk close to the Sun and are exposed to its intense light for a day or so before they are flung by the X-wind to much larger distances. Chondrules were melted, perhaps many times, by flares at larger distances from the Sun before being launched and annealed, but not remelted, in the X-wind. Aerodynamic sorting explains the narrow range of sizes with which CAIs and chondrules are found in chondritic meteorites. Flare-generated cosmic-rays may induce spallation reactions that produce some of the short-lived radioactivities associated with primitive solar system rocks. This revised version was published online in June 2006 with corrections to the Cover Date.     

The nature of the luminous blue variable AG carinae

After many years of permanence at minimum, the luminous blue variable AG Car started in mid 1990 a new brightening phase. We review the spectroscopic variations of the star since 1949, and discuss the nature of the circumstellar nebula. We give evidence that, like in Car, also in AG Car dust is continuously condensing from the stellar wind. We suggest that the star could be partially reddened by the circumstellar dust, which could affect the estimates of the stellar distance. An extended HII halo is present outside the ring nebula, which should be associated with the wind of a previous cooler evolutionary stage of AG Car.     

Observations of the atmospheres and winds of O-stars,LBVs and Wolf-Rayet stars

This review summarises recent studies of O-stars, Luminous Blue Variables (LBVs) and Wolf-Rayet (WR) stars, emphasising observations and analyses of their atmospheres and stellar winds yielding determinations of their physical and chemical properties. Studies of these stellar groups provide important tests of both stellar wind theory and stellar evolution models incorporating mass-loss effects. Quantitative analyses of O-star spectra reveal enhanced helium abundances in Of and many luminous O-supergiants, together with CNO anomalies in OBN and Ofpe/WN9 stars, indicative of evolved objects. Enhanced helium, and CNO-cycle products are observed in several LBVs, implying a highly evolved status, whilst for the WR stars there is strong evidence for the exposition of CNO-cycle products in WN stars, and helium-burning products in WC and WO stars. The observed wind properties and mass-loss rates derived for O-stars show, in general terms, good agreement with predictions from the latest radiation-driven wind models, although some discrepancies are apparent. Several LBVs show similar mass-loss rates at maximum and minimum states, contrary to previous expectations, with the mechanism responsible for the variability and outbursts remaining unclear. WR stars exhibit the most extreme levels of mass-loss and stellar wind momenta. Whilst alternative mass-loss mechanisms have been proposed, recent calculations indicate that radiation pressure alone may be sufficient, given the strong ionization stratification present in their winds.     

高超声速化学非平衡粘性激波层方程的数值解

本文讨论了高超声速粘性激波层方程数值计算时差分格式引起的物理失真问题。具体分析了全隐格式格式粘性的影响,并作了数值试验。为了验证隐式结果的可靠性。在超声速激波风洞中测量了钝锥的表面压力分布,并与计算结果作了比较,两者基本一致。 本文采用隐式有限差分法数值计算了高超声速化学非平衡粘性激波层绕细长球锥的流动。计算时采用连续方程和法向动量方程耦合求解的方法以解决细长体远后身区计算中的问题。应用网格技术和加强系数矩阵主对角元素优势的方法提高了化学非平衡流计算的雷诺数范围。文中给出了高超声速化学非平衡流的计算结果,并与其它文献的结果作了比较。     

稳定状态下锥形伞结构分析

通过合理简化和假设确定轴对称锥形降落伞模型，建立了充满稳定状态下锥形伞受力平衡微分方程，然后根据空间几何关系和弹性力学，补充约束方程，通过数值方法求解方程，最终得到伞绳和伞衣的形状和应力。编成非线性迭代程序对锥形伞进行验证。算例表明，该模型可以用于锥形伞结构的初步分析和设计。     

飞机在变化风场中三维运动的数值仿真

本文在引入和定义了必要的坐标系和Euler角以后,推导了计及任意变化风场的飞机一般运动方程.所得的两组运动方程均适宜于在大气紊流和风切变中飞机三维飞行运动的数值仿真。还讨论了风梯度的气动力效应。     

低速实壁风洞壁压信息洞壁干扰修正法

本文简要介绍、推导了低速实壁风洞洞壁干扰修正壁压信息矩阵法的出发方程组及其具体的解,给出了试验结果修正公式及本文方法的数值模拟检验和模型试验检验结果与分析,并对模型后掠角、攻角,模型安装偏离风洞轴线的影响,洞壁干扰轴向迁移加速度效应的修正和试验段长度影响等问题作了计算、分析和讨论。     

一种求解透平叶栅三维流场的高精度TVD格式

本文提出了一种应用三阶精度Chakravarthy-OsherTVD格式求解环形透平叶栅三维定常流场的隐式近似因子分解方法。控制方程为柱座标速度分量表示的任意曲线座标系下的三维欧拉方程。采用Beam-Warming近似分解, 对隐式项进行迎风差分, 得到了时间精度为一阶、空间精度为5点三阶的隐式格式。算例对5点三阶和5点二阶精度的格式进行了比较。表明空间三阶精度隐格式对计算结果没有明显改进, 但收敛残差有较大降低。      

Toward an Understanding of the Systematic Uncertainties in Deriving the Primordial Helium Abundance from H II Region Observations

Recent determinations of the primordial He abundance have given significantly different results. We are attempting to identify some of the causes of these differences and propose observational solutions. Here we identify a systematic difference in how the data are interpreted (differences in corrections for the presence of neutral helium) and the importance of a systematic bias towards lower derived helium abundances (underestimating the presence of underlying stellar absorption).     

Radiation driven winds of hot stars: Theory of O-star atmospheres as a spectroscopic tool

The status of the continuing effort to construct radiation driven wind models for O-Stars atmospheres is reviewed. Emphasis is given to several problems relating to the fomation of UV line spectra the use of accurate atomic data, the inclusion of EUV radiation by shock heated matter, the simulation of photospheric line blocking.A new tool for O-star diagnostics is presented. This is based on the use of wind models to calculate synthetic high resolution spectra covering the observable UV region. A comparison with observed spectra then gives physical constraints on the properties of stellar winds and stellar parameters, additionally abundances can be determined.The astrophysical potential of this method is demonstrated by an application to two Of-stars, the galactic O4f-star -Puppis and the LMC O3f-star Melnick 42. With regard to effective temperatures and gravities, the results from the application of classical methods to the analysis of photospheric lines are only partially verified. Explanations for the shortcomings of classical NLTE methods are discussed.