湍动等离子体散射对天体X射线谱的作用

天体(包括太阳)活动区常常伴随着出现等离子体湍动。这种湍动的散射作用,势必会大大改变该区产生出来的辐射谱的特征及“大气”结构。观测到的宇宙X射线源大多数具有较大的辐射谱指数,用通常的康普顿机制(或同步加速机制)来解释这种谱特征是困难的。但是,考虑到等离子体湍动散射对辐射转移过程的作用,这种困难即可克服,并可在很宽的谱指数范围内与观测谱相拟合。本文具体研究了等离子体湍动散射对康普顿过程的作用,得到了甚宽的X射线辐射谱,并从理论上得出了对应活动区的大气结构模型,与经验模型相吻合。这表明,考虑等离子体湍动散射对天体活动区所产生的辐射的作用是很重要的。     

边缘耀斑中HeI 10830 A的加宽计算

讨论了HeI 10830 A的Doppler和Stark加宽机制以及各种加宽参数的计算,并得到以下一些结论辐射阻尼对HeI 10830 A的加宽作用与Doppler效应相比可以忽略;在公认的耀斑电子密度(Ne=3.2×1013 cm-3)的情况下,所有阻尼项均不可能产生可以觉察的加宽;直到Ne=1015 cm-3,各种阻尼对线心半宽的增加都不起作用,其值最多在10-aA的量级,因此,线心都可以看作是Doppler加宽;当Ne＞1014 cm-3时,Stark加宽,特别是电子碰撞的Stark加宽将在HeI 10830 A的加宽中起主要作用;如要Stark加宽谱线的线翼比纯Doppler加宽大1-2倍,则阻尼加宽半宽与△λD可以相比拟;如果用Stark加宽来解释1989年边缘耀斑的观测轮廓,则电子密度将达1017cm-3;与氦原子的碰撞阻尼(γ3)造成的加宽对I12和I3两分量明显不同,它们对I12的影响比对I3的影响大近一个量级.我们的观测显示I12和I3线翼的延伸基本一样,因而我们的观测轮廓不可能是γ3造成的.     

两个大环状日珥群H_α单色光与光谱的同时观测

利用南京大学太阳塔,我们观测到1982年12月20日和1983年2月9日出现在日面西边缘的两个大环状日珥群。由同时获得的H_α单色光照相资料H_α、CallH·K线光谱资料测出了环内物质的视向速度分布,该分布与假定物质沿环无粘滞的自由下落推算出的视向速度分布相一致。利用H_α和K线的半宽求出了环内物质的运动温度及湍动速度,温度分布比较均匀,湍动速度随日面高度而增加。利用K线和H线线心强度之比,推算了环内物质的密度,得到氢原子密度为1.3—2.6×10~(10)cm~(-3),另外,还通过估算环珥群的总能量来讨论了环珥群与耀斑的关系。     

活动星系核中相对论电子束的物理效应

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。     

小质量X射线双星铁发射线观测特征的理论分析

小质量Ｘ射线双星在６－７ｋｅＶ的铁发射线具有一些明显观测特征，如谱线展宽、红移和轮廓非对称性。这些性质可能是由高价Ｆｅ离子发射线光子穿过致密天体周围较“冷”等离子体介质时的康普软化过程所造成，本文按此模型求解了康普软化扩散方程，所得理论谱线轮廓与观测线拟合得很好。拟合参量（等离子体的汤姆孙散射光深）取为τｅ～３，由此定出散射等离子体电子密度Ｎｅ≈１０＾１６ｃｍ＾－３，散射球半径Ｒ≈１０＾９ｃｍ．     

W51M分子云中H和He复合线的观测研究

W51M (W51 Main)是一个和HⅡ区成协的大质量恒星形成区,在其中可以探测到众多的分子谱线和H、He射电复合线.中国科学院上海天文台基于天马65 m望远镜对W51M的观测数据,证认了主量子数在74–117之间的H、He复合发射线,其中主量子数在74–78之间的H和He的α复合线均被探测到.结合H和He复合线的多普勒致宽,算出该HⅡ区的电子温度约为7400 K, He+/H+的离子丰度比约为0.09,这与已有的研究基本吻合.考虑高信噪比的复合线,即H(n)α(74n78),计算得出W51M的平均湍动速度是13.767 km·s-1.通过确定W51M或其他HⅡ区中的复合线,获取电子温度、湍动速度以及其他物理参量,在电子数密度、元素丰度、恒星形成率等方面进行了探讨,对分子谱线以及其他波段的复合线研究具有借鉴意义.     

天体H_2O分子谱线的观测和研究

本文评述了1968年发现天体H_2O分子谱线以来其观测和研究的进展。内容包括(1)天体H_2O脉泽和正常H_2O分子的观测特征;(2)在恒星早期和晚期演化过程中H_2O分子所起的作用和它们可能的状态;(3)利用H_2O分子谱线的观测,研究晚型星拱星包层结构和速度流场、恒星质量损失率以及恒星早期演化过程中的分子云能量平衡等理论研究成果;(4)H_2O脉泽时变特征的观测和研究;(5)银河系天体H_2O(6_(16)-5_(23))脉泽源巡视和H_2O脉泽源星表以及河外H_2O脉泽源的探测。     

质子耀斑爆发相的粒子加速

本文从粒子分布函数所满足的带有规则电场的准线性方程出发,得到了包含有规则电场与湍动起伏场相互耦合作用在内的等效动量空间扩散系数,提出了太阳质子耀斑中性片中的规则电场与湍动起伏场的联合加速机制。根据太阳质子耀斑的物理条件,计算表明荷电粒子在中性片中可以被有效地加速,能量可以达到～20MeV,甚至～1GeV。本文证明了离子声湍动起伏场与规则电场的联合加速机制有效地使质子和其它重离子注入到Langmuir湍动加速区中去;并且表明,在Langmuir湍动起伏场与规则电场联合加速的情形下,可以得到与观测事实符合得较好的高能质子的谱以及高能电子的幂律分布的谱。     

类铍氧离子X射线及EUV光谱理论模拟

根据非局域热动平衡状态下谱线形成理论，利用相对论多组态原子程序软件包FAC模拟了类铍氧离子的X射线及EUV光谱．分析了间接过程对类铍氧离子X射线及EUV光谱形成的影响．在典型天体等离子体密度(ne=10加／立方厘米)情况下，采用了3种模型，在不同温度下模拟X射线及EUV光谱形成过程，分析比较了间接过程对谱线形成的贡献，并给出了它们的速率系数，得出了在谱线形成过程中，间接过程具有非常重要的作用．     

Line formation in magnetic fields

Hyder (1968) has suggested that longitudinal magnetograph measurements of weak magnetic fields in prominences have underestimated field strengths as the result of zero-field levelcrossing interference (the Hanle effect). Hyder (1968) also suggested that resonance polarization effects have sometimes led to errors in measurements of the transverse component of magnetic fields. Stenflo (1969) has pointed out some errors in Hyder's paper, while contending that the Hanle effect is implicitly included in current theories of line formation in the presence of Zeeman splitting.In the present Note these questions are re-examined using the results of a density matrix treatment of absorption, emission, and scattering processes. The basic conclusions are as follows: (1) Longitudinal magnetograph measurements using optically thin lines are not influenced by the Hanle effect. (2) Although present theories of line formation in magnetic fields do not include the Hanle effect, this omission is generally unimportant for lines formed in the photosphere and lower chromosphere due to rapid collisional depolarization of atomic levels. (3) For the same reason, other resonance polarization effects are probably too small to cause significant errors in magnetograph measurements of all but the very weakest magnetic fields, when photospheric and lower chromospheric lines are used. (4) By contrast, the general phenomenon of atomic level polarization is quite important in most prominences. As emphasized by Hyder, extreme care must be used in selecting lines for magnetograph studies of solar magnetic fields.     

Correlation Height of the Source Region of Si II Emission Lines in Coronal Hole Regions

The height of the source region of Si II emission lines characterizes the height of the bottom layer of solar atmosphere's transition region. The correlation analysis of the intensities of ultraviolet spectral lines and the threedimensional structure of magnetic field yielded by force-free extrapolation is a new method for determining the height of ultraviolet emission lines’ source region. It has been found that the height thus obtained is larger than that given by traditional viewpoint. Because the existing numerical analyses with this method are scarce, this result has to be further verified with more observational materials. In this work, this method is applied to the Si II emission lines observed by SOHO/SUMER for the solar surface region beneath the solar coronal hole at southern pole and to the magnetic fields measured by National Solar Observatory/Kitt Peak (NSO/KP) in U.S.A. The correlation height of the source region of Si II emission lines in coronal hole region is approximately 5.0 Mm. This result supports the conclusion that the height of the bottom layer of transition region in coronal hole region is larger than that in quiet regions. Moreover, some new phenomena have been discovered and their causes are probed.     

VLBI Observations of OH stars: S Persei

The masers in three stars, S Per, OH53.6-0.2 and VXSgr, were observed in the main lines of OH at λ18 cm in March 1997 with a VLBI array consisting of 6 EVN antennas and 3 in the USA. Both S Per and VX Sgr were detected on transatlantic baselines, showing that at least some of the maser spots are very compact with sizes less than around 2 mas. The observations confirm that in S Per there is main line OH emission close to star at a similar distance (≈ 100 AU) as the H₂O shell. The most blue-shifted emission comes from the centre of the object suggesting radial amplification of the maser radiation, whilst most of the remainder comes from a thick shell, some 100 AU from the star. This contrasts with the 1612 MHz OH emission that comes from an outer shell some 1000 AU from the star. Estimates of the magnetic fields in the shell from Zeeman pairs in S Per show fields of a few hundred nT.     

Computation of inner coronal magnetic fields from longitudinal field components on a spherical photosphere

A method is developed which for a certain day permits the approximate calculation of closed small and large scale magnetic field lines. From the photospheric longitudinal components of the magnetic field measured at this day normal components are derived taking into account the curvature of the solar surface. The magnetic fields are assumed to be potential or force-free fields.The method is applied to observations of September 5 and September 7, 1973. The projected magnetic field lines are compared with the loop structures which are visible in XUV pictures taken on these days. In the cases where no good agreement could be obtained for potential fields, force-free fields are calculated and fitted to the observed structures.     

Line formation in microturbulent magnetic fields

The formation of Zeeman lines in Gaussian microturbulent magnetic fields is considered assuming LTE. General formulae are derived for the local mean values of the transfer matrix elements. The cases of one-dimensional (longitudinal), isotropic, and two-dimensional (transversal) magnetic microturbulence are studied in some detail. Asymptotic formulae are given for small mean as well as for small microturbulent magnetic fields. Characteristic effects of magnetic microturbulence on the transfer coefficients are: (i) the broadening of the frequency contours, although only for the case of longitudinal Zeeman effect and longitudinal magnetic microturbulence this effect can be described analogous to Doppler broadening, (ii) the appearance of a pseudo-Zeeman structure for nonlongitudinal magnetic microturbulence, (iii) the reduction of maximal values of circular polarization, and (iv) the appearance of characteristic linear polarization effects due to the anisotropy of the magnetic microturbulence.Line contours and polarization of Zeeman triplets are computed for Milne-Edddington atmospheres. It is shown that magnetic intensification due to microturbulent magnetic fields may be much more efficient than that due to regular fields. The gravity center of a Zeeman line observed in circularly polarized light remains a reasonable measure of the line of sight component of the mean magnetic field for a line strength47-1. For saturated lines, the gravity center distance depends significantly on the magnetic microturbulence and its anisotropy. The influence of magnetic microturbulence on the ratio of longitudinal field magnetographic signals shows that unique conclusions about the magnetic microstructure can be drawn from the line ratio measurement only in combination with further spectroscopic data or physical reasoning.     

How To Use Magnetic Field Information For Coronal Loop Identification

The structure of the solar corona is dominated by the magnetic field because the magnetic pressure is about four orders of magnitude higher than the plasma pressure. Due to the high conductivity the emitting coronal plasma (visible, e.g., in SOHO/EIT) outlines the magnetic field lines. The gradient of the emitting plasma structures is significantly lower parallel to the magnetic field lines than in the perpendicular direction. Consequently information regarding the coronal magnetic field can be used for the interpretation of coronal plasma structures. We extrapolate the coronal magnetic field from photospheric magnetic field measurements into the corona. The extrapolation method depends on assumptions regarding coronal currents, e.g., potential fields (current-free) or force-free fields (current parallel to magnetic field). As a next step we project the reconstructed 3D magnetic field lines on an EIT-image and compare with the emitting plasma structures. Coronal loops are identified as closed magnetic field lines with a high emissivity in EIT and a small gradient of the emissivity along the magnetic field.     

A possible lunar outcrop: a study of lunokhod-2 data

The remotely controlled vehicle Lunokhod-2 travelled extensively around the edges of a linear depression unofficially called Fossa Recta. The edges of the Fossa are marked by elongated boulder fields. Three lines of reasoning suggest that the boulder fields are not the usual erratic boulders found on a normal mare surface, but are bedrock protuberances: (1) The morphology of many boulders is reminiscent of primary lava features, (2) toward the edge of the Fossa the regolith thins out; (3) a model of lunar gardening indicates that no regolith is to be expected in the upper portion of a non-impact cliff.Part of the research was conducted while L.B.R. was a participant of an exchange program between the Academy of Sciences, U.S.S.R. and the Academy of Sciences, U.S.A.     

Magnetic field measurements of CP stars from hydrogen line cores

We present the results of measurements of magnetic fields of chemically peculiar (CP) stars, performed from the shifts between the circularly polarized components of metal and hydrogen lines (the Babcock method). The observations are carried out with an analyzer of circular polarization at the 6‐m telescope of the SAO RAS. We found that for the absolute majority of the objects studied (in 22 CP stars out of 23), the magnetic fields, determined from the Zeeman shifts in the hydrogen line cores, are significantly lower than those obtained from metal lines in the same spectra. This disparity varies between the stars. We show that instrumental effects can not produce the above features, and discuss the possible causes of the observed effect. The discovered condition reveals a more complicated structure of magnetic fields of CP stars than a simple dipole, in particular, a reduction of the field strength in the upper atmosphere with the vertical gradient, significantly higher than the dipole (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Latitude dependence of magnetic field-line inclinations

It is shown that leading and following magnetic field lines are inclined toward each other by a few degrees at nearly all latitudes in both the north and south hemispheres. The amplitudes of these inclinations are lower by about a factor 3 for weak fields than for strong fields. There are significant differences between the hemispheres and from one activity cycle to the next in the leading and following polarity field-line inclinations at latitudes poleward of the activity latitudes. In a narrow latitude zone just south of the solar equator the inclinations of both the leading and following fields reduce to zero (or perhaps slightly negative values). Although one would expect such a zone at the equator, where diffusion will mix field lines with opposite inclinations from the two hemispheres, it is not clear why this zone should be on one side of the equator only. The results discussed here were obtained with Mount Wilson magnetograph data (1967–1992), and are confirmed in many respects with National Solar Observatory/Kitt Peak (NSO/KP) data (1976–1986).Operated by the Association of Universities for Research in Astronomy, Inc., under Cooperative Agreement with the National Science Foundation.