Density and temperature diagnostics of solar emission lines from Navii and Alix

Line intensity ratios of EUV emission lines from Navii and Alix have been considered for electron density and temperature determinations within the chromosphere-corona transition region and the corona. The electron pressure within the emission region has been assumed to be a constant parameter. Theoretical line intensities for these ions have been computed using a model solar atmosphere and compared with the values as observed by ATM ultraviolet spectrometer. The observed intensities correspond to the average quiet-Sun conditions near solar minimum.     

Dust acoustic solitary waves in dusty plasma with nonthermal ions

In this paper, the characteristics of the dust acoustic solitary waves in dusty plasmas are studied. The distribution of ions is nonthermal, and the nonthermal parameter is treated as a variable. The pseudo-potential method has been used to investigate the possibility of soliton formation. We show that for some values of the nonthermal parameter there is no soliton.     

Observations of photospheric faculae at the center of the solar disk

Methods for the determination of the average optical depth of formation of weak Fraunhofer lines are compared, and their relative merits are discussed. Distinction should be made between the region of origin of the emergent radiation, and of the line depression. For weak or fairly weak lines the average optical depth of formation of the line depression is the relevant quantity; it should be determined by using a computational scheme based on the classical weighting functions of line formation; other methods give physically unsignificant or conflicting results.

     

Analytical solutions for saturated P Cygni type profiles

Analytical formulae for single P Cygni type saturated resonance line profiles in stellar winds have been derived. The limbdarkening and presence of underlying intrinsic atmospheric profile have been ignored. The Sobolev approximation for radiative transfer has been used and the general velocity law has been specified by widely used β parameter. The analytical formulae for the saturated resonance line profiles can be found for cases when 2β is an integer. The formulae for 2β = 1,2, 3 and 4 have been found by us. Also the formulae for calculating the line profiles in the cases of external and internal sharp truncation (cutoff) of the scattering shell have been given. Some characteristic line profiles have been presented. It has been shown that the turbulence-generated isotropic dominant backscattering of radiation in stellar winds generates wide dark plateaux in the blue wings of spectral lines, and the slopes of plateaux are shaped by turbulence. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of Strömgren spheres on the line formation inζ Aur systems

Aur binaries are particularly well suited for the study of the winds of late type supergiants. The analysis technique is based on theoretical modelling of flux profiles which are formed by resonance scattering in the expanding envelope. However, the hot B star ionizes the wind and can produce a considerable H II region around the B star. In order to investigate the influence of the Strömgren sphere on the line formation we have calculated theoretical P Cyg line profiles with an H II region. The line source function is solved with the Sobolev method followed by a correct formal integration (Hempe, 1982). The ionization of metals within the H II region is described by an ionization parameter which mimics the typical ionization fraction of the relevant ions. The resulting line profiles are dependent on the geometric shape of the H II region, the velocity distribution, and the opacity parameter. The reduced absorber density within the H II region produces weakened line profiles and the specific geometry of the H II region influences the emission and the absorption component in different ways. The careful analysis of model computations suggests that the region of the line formation is not only restricted to the vicinity of the B star, hence the outer integration boundary has to be taken to a sufficiently large radius in the calculation of line profiles.     

Bianchi type-V bulk viscous cosmological models with particle creation in Brans-Dicke theory

The Bianchi type-V cosmological model with viscous fluid and creation particle in Brans-Dicke theory has been considered. The present paper deals with Bianchi type-V cosmological model with bulk viscosity and particle creation described by full causal thermodynamics in Brans-Dicke theory. We have discussed two types of solutions of the average scale factor for a Bianchi type-V model by using a variation law of Hubble’s parameter, which yields a constant value of the deceleration parameter. The exact solutions to the corresponding field equations are obtained in quadrature form. The solutions to the Einstein field equations are obtained for power law and exponential form. The cosmological parameters have been discussed in detail.     

Holographic dark energy model with linearly varying deceleration parameter and generalised Chaplygin gas dark energy model in Bianchi type-I universe

The paper deals with a spatially homogeneous and anisotropic Bianchi type-I universe filled with two minimally interacting fluids; matter and holographic dark energy components. The nature of the holographic dark energy for Bianchi type-I space time is discussed. An exact solution to Einstein’s field equations in Bianchi type-I line element is obtained using the assumption of linearly varying deceleration parameter. Under the suitable condition, it is observed that the anisotropy parameter of the universe approaches to zero for large cosmic time and the coincidence parameter increases with increasing time. We established a correspondence between the holographic dark energy models with the generalised Chaplygin gas dark energy model. We also reconstructed the potential and dynamics of the scalar field which describes the Chaplygin cosmology. Solution of the field equations shows that a big rip type future singularity will occur for this model. It has been observed that the solutions are compatible with the results of recent observations.     

An analytical model of the SiO maser velocity spectrum

SiO maser sources associated with Mira variables show a wide velocity spread in the spectral line and a variety of profiles. We think this velocity spread may be ultimately traced to the star's pulsation. We consider the propagation of a perturbation generated by the pulsation in the circumstellar envelope, regarded as a compressible fluid. Using observed average parameter values for the Mira stars, our model gives, at the distance of the SiO maser, a velocity spread of ±6 km/s, in good agreement with the observed widths. The question of a correlated variation of the line width with the optical phase is also discussed     

太阳大气中氢原子的赖曼谱线

氢是太阳大气中最主要的元素。氢原子的赖曼(Lyman)谱线,尤其是赖曼阿尔法(Ly-α)谱线的辐射,是太阳色球和低过渡区能量损失的主要形式。在太阳的赖曼α像中,网络组织的辐射比较强,而辐射最强的地方是活动区。由于存在辐射转移效应,在宁静区,低阶赖曼谱线的谱形中央一般会形成一个凹陷,而在中央两侧则形成两个峰,两峰往往呈现出一定的不对称性。数值模拟和观测研究表明,赖曼谱线双峰的不对称性与高层大气中各种系统性流动有关。在太阳活动区,赖曼谱形在谱斑区与在宁静区类似;而在黑子区,赖曼谱形几乎没有中央凹陷。赖曼谱形也可用于诊断日珥、耀斑和日冕物质抛射等结构和现象的等离子体特性。该文回顾了赖曼谱线的观测历史,阐明了观测与模拟结果所揭示的物理过程,并结合笔者的认识进行了相应的评论。     

Non-LTE resonance line polarization with partial redistribution: The solar Ca II K line

The non-LTE equations for the transfer of polarized radiation are solved for a two-level model of the Ca ii K ion in the atmospheric models of Gingerich et al. (1971) and Vernazza et al. (1981). The line formation model treats partial redistribution effects, including collisions. The effects of magnetic fields and of quantum mechanical interference are neglected. The response of the intensity, percentage polarization and Q Stokes parameter to changes in the calcium abundance, van der Waals damping parameter and atmospheric models is discussed.     

A generalized theory for line formation in a homogeneous magnetic field

The formation of spectral lines in a homogeneous magnetic field has been studied. A new method for solving the transfer equations for polarized light has been found. Using this method, the Stokes parameters may be derived without any special assumptions regarding the model atmosphere. With the line formed by pure absorption, the expressions for the Stokes parameters may easily be adapted to numerical calculations. In order to illustrate the method, the line profile for the Zeeman triplet 5250 has been calculated using a photospheric model atmosphere.     

Scaling-law equilibria for calcium in canopy-type models of the solar chromosphere

Scaling laws for resonance line formation are used to obtain approximate excitation and ionization equilibria for a three-level model of singly ionized calcium. The method has been developed for and is applied to the study of magnetograph response in the 8542 Å infrared triplet line to magnetostatic canopies which schematically model diffuse, nearly horizontal fields in the low solar chromosphere. For this application, the method is shown to be efficient and semi-quantitative, and the results indicate the type and range of effects on calcium-line radiation which result from reduced gas pressure inside the magnetic regions.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.     

A review of diagnostic emission line ratios in the Narrow Line Region of Active Galactic Nuclei

The availability of new observing facilities both from ground and space such as the Keck 10m telescope and the Hubble Space Telescope is casting new light on the spectroscopic investigation of emission line galaxies. In particular, it is now possible to detect spectra with a significantly improved signal to noise ratio in a very wide wavelength range, from the ultraviolet to the near infrared (HST, Keck) and beyond (ISO is unveiling the far infrared domain). As we move to high redshifts, however, it is more likely that the observed spectra are given by the contribution of different components in the galaxy: in particular, this may be the case if an Active Galactic Nucleus (AGN hereafter) emitting a power-law continuum is surrounded by regions with strong star formation activity. The identification of the source which ionizes the line emitting regions is then complicated by the fact that we are observing the integrated spectrum from regions which are ionized by different sources. In this paper we wish to review which line ratios may be used in order to discriminate between photoionization by young stars and power-law continuum in the wavelength range from 1200 Å to 100 μm. To this aim we used the photoionization code Cloudy (Ferland 1996) to present a series of diagnostic diagrams showing the dependence of emission line ratios on the main input parameters of photoionization models in the case of one component models with gaseous clouds ionized by (1) a stellar continuum typical of an HII region and (2) a power-law continuum typical of an AGN: these line ratios are plotted as isoratio maps for different values of the hydrogen density, ionization parameter and slope of the power-law continuum. We then show how the results may be affected by more realistic assumptions about the environment of the ionized gas: to this aim, we show the effects on selected line ratios of (a) the presence of two populations of clouds with different densities and (b) an AGN surrounded by regions with strong star formation activity.     

Illuminating protogalaxies? The discovery of extended Lyman-α emission around a QSO at z=4.5

We have discovered extended Lyman-α emission around a z=4.5 QSO in a deep long-slit spectrum with Keck/LRIS at moderate spectral resolution (R≈ 1000). The line emission extends 5 arcsec beyond the continuum of the QSO and is spatially asymmetric. This extended line emission has a spectral extent of 1000km/s, much narrower in velocity spread than the broad Lyman-α from the QSO itself and slightly offset in redshift. No evidence of continuum is seen for the extended emission line region, suggesting that this recombination line is powered by reprocessed QSO Lyman continuum flux rather than by local star formation. This phenomenon is rare in QSOs which are not radio loud, and this is the first time it has been observed at z>4. It seems likely that the QSO is illuminating the surrounding cold gas of the host galaxy, with the ionizing photons producing Lyman-α fluorescence. As suggested by Haiman and Rees (2001), this `fuzz' around a distant quasar may place strong constraints on galaxy formation and the extended distribution of cold, neutral gas. This revised version was published online in August 2006 with corrections to the Cover Date.     

The effect of electron scattering on curves of growth

A new exact solution of the macroscopic line transfer equation including electron scattering terms has been obtained for a Milne-Eddington Model atmosphere, and curves of growth based on this solution have been calculated. The results indicate that for lines formed by scattering there is a systematic change in the appropriate theoretical curve of growth as electron scattering becomes an increasingly important source of continuous opacity. In a case where electron scattering is the dominant opacity source, the abundance necessary to produce a given line strength may be decreased by a factor of 2–5 and the derived velocity parameter decreased by 20–30% due to the shifts in the theoretical curves.Contributions from the Kitt Peak National Observatory No. 416.Operated by the Association of Universities for Research in Astronomy, Inc. under contract with the National Science Foundation.     

The molecular emission-line spectrum of IRC +10216 between 330 and 358 GHz

We have conducted a spectral line survey of IRC +10216 using the Caltech Submillimeter Observatory to an average sensitivity of < or approximately 95 mK. A deconvolution algorithm has been used to derive the continuous single-sideband spectrum from 330.2 to 358.1 GHz. A total of 56 spectral lines were detected of which 54 have been identified with 8 molecules and a total of 18 isotopomers. The observed lines are used to derive column densities and relative abundances for the detected species. Within this frequency range the spectral lines detected contribute the majority of the total flux emitted by IRC +10216. We use the derived column densities and excitation temperatures to simulate the molecular line emission (assuming LTE) at frequencies up to 1000 GHz. The observed and simulated flux from line emission is compared to broadband total flux measurements and to dust emission assuming a power-law variation of the dust emissivity. We conclude that significant corrections for the line flux must be made to broadband flux measurements of IRC +10216 at wavelengths longer than approximately 750 micrometers.     

13mm低温制冷谱线接收系统和星际水分子观测研究

为了开拓短厘米波单天线星际分子的观测和研究,在乌鲁木齐天文站２５ｍ射电望远镜１３ｍｍ低温制冷接收机的基础上,配置了声表面波频谱仪和谱线数据采集系统,组成了１３ｍｍ低温致冷谱线接收机．接收机前端是一个工作在低温２０Ｋ的低噪声放大器,本振是２２ＧＨｚ的锁相源．接收机的平均噪声温度为５０Ｋ．后端是一个宽带的（４０ＭＨｚ）高分辨率（４０ｋＨｚ）的声表波频谱仪．利用这套系统观测了一批已知的水脉泽源,观测系统正常,结果合理．观测结果表明,乌鲁木齐天文站良好的站址和２５ｍ射电望远镜给厘米波段星际分子谱线观测提供了一个很好的条件．     

双黑洞系统的不同起源及其参数分布

双黑洞组成的近密双星系统并合是激光干涉仪引力波天文台等地基引力波探测器的主要探测对象。随着探测器灵敏度的提高,大量该类信号的探测将成为进一步研究黑洞物理的有效工具。但是目前对双黑洞系统的起源机制和内禀参数分布等物理问题的研究还不够深入,例如由引力波探测得到的黑洞质量分布与X射线双星观测的结果存在较大差异,还未有很好的理论模型可解释该结果。目前普遍认为双黑洞系统主要有两种起源:大质量双星演化机制和动力学起源机制。基于这两类起源的双黑洞系统在质量、自旋分布等方面存在差异。因此可在贝叶斯理论框架下,利用引力波信号携带的波源质量和自旋等信息,推断波源起源,计算不同起源的双黑洞系统所占比例,以及检验质量自旋等参数分布的差异。     

Emission Line Profiles of Warped Disks in the Kerr Spacetime

The calculations of emission line pro?les of a warped disk in the Kerr spacetime have been discussed in this paper. The main content consists of two parts. In the ?rst part, the geodesic motion in the Kerr spacetime and the equations of motion in integral form, as well as the method to obtain the solution with the Weierstrass’ elliptic functions are presented. Using the Weierstrass’ elliptic functions, the Boyer-Lindquist (B-L) coordinates and the affine parameter o are semi-analytically expressed as the functions of a parameter p. Then a code named ynogk (Yunnan Observatory Geodesic Kerr) is introduced based on the above discussions to calculate very fast the null geodesic in the Kerr spacetime. As an application of ynogk, the emission line pro?les of warped disks are investigated in detail in the second part of this paper. Here the structure model of warped disks is based on the results of Bardeen and Petterson in 1975, and the line pro?les are computed with the ray tracing method. Finally, the discussions and conclusions of the calculated results are presented. It is indicated that the line pro?les are dependent mainly on the inclination and azimuthal angles of the observer, as well as the index of emissivity, and that they may have a triple-peaked even multi-peaked structure, different from the double-peaked structure in the line pro?les of a standard thin accretion disk.