共查询到20条相似文献，搜索用时 93 毫秒
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恒星起源的早期阶段与双极分子流出物有关。这种集束流的典型例子可在暗云L1551中找到。从它的中心源IRS5向着蓝移了的流出物方向,有一窄条喷流射出。喷流的光谱类似于低激发度HerbigHaro天体的光谱,为激波激发型。喷流中流出物的 相似文献
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随着探测设备角分辨率和灵敏度的提高,喷流、喷流节点和热斑等活动星系核延展结构在射电、红外、光学、X射线等越来越多的波段被探测到,分辨出其更细致的结构,促进了理论研究热潮的兴起,使该领域成为当今天体物理研究的活跃领域之一。喷流是由活动星系核中心产生的准直等离子体外流,由中心黑洞驱动。至今,对喷流的成分、产生、准直原理和加速机制等基本问题并不清楚。另一方面,对于喷流、喷流节点和热斑等活动星系核延展区的辐射机制,一般认为其射电和光学辐射由相对论电子的同步辐射产生,但X射线的起源就存在着一定的争议。简单概述该领域近年来观测和理论研究进展。 相似文献
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钱善瑎 《中国天文和天体物理学报》1992,(4)
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。 相似文献
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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． 相似文献
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钱善瑎 《中国天文和天体物理学报》1996,(2)
本文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νm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∝ν，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△Smax（ν）和△t（ν），都具有Blazar天体中观测到的射电爆发的普遍形式．本文提出的激波模型，考虑到驱动气体的持续注入和激波后等离子体的绝热膨胀．因此提供了对相对论喷流中激波形成和演化的物理原因更深入的理解．并对Blazar天体中视超光速节点频谱演化提出了新的解释． 相似文献
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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. 相似文献
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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。 相似文献
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报告分子外流源Ｌ１２１１ 中新发现的１２ 个近红外ＨＨ 天体．在Ｌ１２１１ 的～４’区域,取得了ＪＨＫ’宽带和Ｈ２ ｖ ＝ １０ Ｓ（１） 发射线窄带的近红外图像．分析表明,新探测到的许多红外源与浓密分子云物理成协,其中有２０ 多个源表现出典型的Ｔ Ｔａｕｒｉ 星、Ｈｅｒｂｉｇ Ａｅ／Ｂｅ星和原恒星的红外超．Ｌ１２１１ 中的ＩＲＡＳ点源没有被观测到,可能是更深地埋于分子云中．对红外观测和分子线观测消光估计的比较显示,小于２μｍ 的近红外观测还不足以揭示深埋于分子云的整个年轻星团．根据近红外ＨＨ 天体的形态分布和红外源性质,能进一步证认这些ＨＨ 天体的激发源．其结果表明,Ｌ１２１１ 分子云中具有多个红外源驱动的多个外流活动 相似文献
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本文研究了Ｂｌａｚａｒ天体的辐射性质，提出一种新的喷流模型，即具有幂律分布的极端相对论电子团从中心核注入喷流等离子体中，它在一定的注入速度下，不仅能在喷流等离子体中激发等离子体湍动，产生电磁波的相干辐射，而且能产生强的同步辐射。利用等离子体的弱湍理论，我们研究了极端相对论电子团在喷流等离子体中的辐射过程，并详细研究了它在解释Ｂｌａｚａｒ天体辐射特性中的应用，本文认为，Ｂｌａｚａｒ天体的不稳定辐射与极端相对论电子团的无规注入、喷流等离子体的物理环境瞬息变化有关。Ｂｌａｚａｒ中快速变化的辐射偏振角摆动。产生于相对论电子团在湍动等离子体中的同步辐射过程。另外，Ｘ选和射电选的ＢＬＬａｃ天体之间的区别取决于喷流等离子体的运动状态和物理环境。 相似文献
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This paper reviews the numerical simulations of radiative jets with concrete predictions of the emitted radiation, which can be compared directly with observations of individual HH objects. The only models that have been developed to this point are the “internal working surface model” (in which the structures along HH jets are interpreted as working surfaces resulting from a time-variability in the ejection) or the “Kelvin-Helmholtz instability model” (in which the HH knots are associated with shocks resulting from K-H instabilities in the jet beam/environment boundary). The predictions of intensity maps, line ratios, line profiles and proper motions are discussed. 相似文献
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X. Ribeyre P. Nicolaï S. Galera V. T. Tikhonchuk 《Astrophysics and Space Science》2009,322(1-4):85-90
Supersonic plasma jets are ubiquitous in astrophysics. Our study focus on the jets emanated from Herbig-Haro (HH) objects. They have velocities of a few hundred km/s and are extending over the distances more than a parsec. Interaction of the jets with surrounding matter produces two specific structures in the jet head: the bow shock and the Mach disk. The radiative cooling of these shocks affects strongly the jet dynamics. A tool to understand the physics of these jets is the laboratory experiment. A supersonic jet interaction with surrounding plasma was studied on the PALS laser facility. A collimated high-Z plasma jet with a velocity exceeding 400 km/s was generated and propagated over a few millimeters length. Here we report on study the effect of radiative cooling on the head jet structure with a 2D radiative hydrodynamic code. The simulation results demonstrated the scalability of the experimental observations to the HH jets. 相似文献
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D. C. Gabuzda A. B. Pushkarev T. V. Cawthorne 《Monthly notices of the Royal Astronomical Society》2000,319(4):1109-1124
The results of very long baseline interferometry (VLBI) total intensity ( I ) and linear polarization ( P ) observations at are presented for 10 radio bright BL Lacertae objects. These images complete first-epoch polarization observations for the 1-Jy sample of northern BL Lacertae objects defined by Kühr & Schmidt. Estimates of superluminal speeds are presented for several sources, bringing the total number of sources in the sample for which such estimates are available to 16. Second-epoch observations currently being reduced should yield speed estimates for VLBI features in essentially all the sources in the sample. The jet magnetic fields of these BL Lacertae objects are usually transverse to the local jet direction, but a sizeable minority (about 30 per cent) have VLBI jet components with longitudinal magnetic fields. This may suggest that the conditions in the VLBI jets of BL Lacertae objects are favourable for the formation of relativistic shocks; alternatively, it may be that the toroidal component of the intrinsic jet magnetic field is characteristically dominant in these sources. 相似文献
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Juan P. Madrid William B. Sparks D. E. Harris Eric S. Perlman Duccio Macchetto John Biretta 《Astrophysics and Space Science》2007,311(1-3):329-333
Near-ultraviolet imaging with HST offers the best possible spatial resolution currently available for optical/UV astronomical
imaging. The giant elliptical galaxy M87 hosts one of the most spectacular, best studied and nearest (d=16 Mpc) galactic-scale relativistic (synchrotron emitting plasma) jets. We have extracted from the HST archive all 220 nm
images of the jet of M87, taken with the STIS MAMA camera and co-added them to provide the deepest image ever at this wavelength.
The combination of highest spatial resolution and long integration time, 42500 seconds, reveals a wealth of complex structure,
knots, filaments and shocks. We compare this image with deep X-ray observations obtained with the Chandra X-ray telescope. 相似文献
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A. C. Raga 《Astrophysics and Space Science》1993,208(2):163-189
A considerable amount of effort has been made towards obtaining a theoretical understanding of the collimated, optically detected outflows (Herbig-Haro objects) ejected by young stars. The most clear results have been obtained for the case of the Herbig-Haro jets, a loosely defined category which groups the Herbig-Haro (HH) objects with jet-like structures of aligned knots. In particular, it has recently been shown that at least some of the characteristics of the HH jets can be straightforwardly explained in terms of models of jets from variable sources. This paper presents a review of the properties of models of jet flows from sources with a variability in the ejection velocity, in the ejection direction, and with a general velocity+direction variability. Also, a comparison between the observational characteristics of HH jets and the predictions from variable source jet models is carried out. 相似文献
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F. Rubini C. Giovanardi S. Lorusso F. Leewin F. Bacciotti 《Astrophysics and Space Science》2004,293(1-2):181-187
Modelling the formation of the maximal emission regions in Herbig-Haro flows, the so-called ‘knots,’ remains a main challenge in the investigation of the YSO's outflows. Recent HST images of optical regions reveal their wide morphological variety. Knotty structures and arc-like regions coexist, suggesting that several mechanisms could be responsible for the global scenario. Arc-like emissions are probably due to other mini-working surfaces or non-axially symmetric interaction of the kinking jet matter with the external medium, while knots seen in [SII] are mostly axially symmetric objects and may have a different origin. In this paper we show that a pattern of regularly spaced, knotty emission regions forms in stationary jets, with emissivity and kinematic features consistent with observations. To this purpose, numerical simulations of non-equilibrium, radiative, hydrodynamical jets in axial symmetric geometry have been performed. 相似文献
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S. A. E. G. Falle 《Astrophysics and Space Science》1994,216(1-2):119-125
Despite its title, this paper is mainly concerned with some of the latest theoretical work on the Herbig-Haro (HH) objects associated with stellar jets. Recent measurements of the proper motions of HH objects show that even those near the source are moving at about the same speed as the jet fluid. This means that they cannot be due to steady shocks in the jet and the only obvious explanation is that the source is varying. 相似文献
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A. Raga L. López-Martín L. Binette J. A. López J. Cantó S. J. Arthur G. Mellema W. Steffen P. Ferruit 《Monthly notices of the Royal Astronomical Society》2000,314(4):681-688
Recent observations show the existence of an increasing number of collimated outflows ejected by young, low-mass stars which are embedded in H ii regions. At distances of a few tens of au from the star, at least one lobe of these outflows will be shielded from the ambient ionizing radiation by the compact, high-extinction circumstellar disc. Within these shielded regions, the jets are probably mostly neutral, similar to the jets in 'normal' Herbig–Haro (HH) objects. At larger distances, these jets emerge into the photoionized nebula, and start to be photoionized by the radiation from the ionizing photon source of the nebula.
In this paper, we model the photoionization of an initially neutral HH jet. This process begins as an ionization front at the side of the jet, which is directed towards the ionizing star of the nebula, and progresses into the beam of the jet. There are two possible solutions. In the first solution, the jet beam becomes fully ionized through the passage of an R-type ionization front. In the second solution, the ionization front slows down enough to become a D-type front (or is already a D-type front at the point in which the jet emerges into the photoionized nebula), forming a partially ionized jet beam, with an expanding photoionized region and a compressed neutral region.
We explore these two types of solutions both analytically and numerically, and discuss the observational effects introduced by this jet photoionization process, concentrating in a region of parameter space that straddles the parameters deduced for HH 444 (the jet from V 510 Orionis). 相似文献
In this paper, we model the photoionization of an initially neutral HH jet. This process begins as an ionization front at the side of the jet, which is directed towards the ionizing star of the nebula, and progresses into the beam of the jet. There are two possible solutions. In the first solution, the jet beam becomes fully ionized through the passage of an R-type ionization front. In the second solution, the ionization front slows down enough to become a D-type front (or is already a D-type front at the point in which the jet emerges into the photoionized nebula), forming a partially ionized jet beam, with an expanding photoionized region and a compressed neutral region.
We explore these two types of solutions both analytically and numerically, and discuss the observational effects introduced by this jet photoionization process, concentrating in a region of parameter space that straddles the parameters deduced for HH 444 (the jet from V 510 Orionis). 相似文献
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The internal structure of stellar jets arising from young stellar objects is characterized by a series of `knots' or condensations which have highly supersonic proper motions. These structures, we believe, are the result of a variable ejection from the source, which leads to the formation of internal working surfaces or small bowshock within the jet beam. In this paper we present a long-slit spectrum of Herbig-Haro object HH 111 obtained with STIS and an interpretation of this observation in terms of an ejection velocity variability model. 相似文献