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1.
It is shown that the dielectronic satellites (DES) dominate X-ray spectral formation in the 6.7-keV K α complex of Fe  xxv at temperatures below that of maximum abundance in collisional ionization equilibrium T m. Owing to their extreme temperature sensitivity, the DES are excellent spectral diagnostics for     in photoionized, collisional or hybrid plasmas; whereas the forbidden, intercombination and resonance lines of Fe  xxv are not. A diagnostic line ratio GD ( T ) is defined including the DES and the lines, with parameters from new relativistic atomic calculations. The DES absorption resonance strengths may be obtained from differential oscillator strengths, possibly to yield the     column densities. The DES contribution to highly ionized Fe should be of interest for models of redward broadening of K α features, ionized accretion discs, accretion flows and K α temporal-temperature variability in AGN.  相似文献   

2.
仲佳勇  张杰  赵刚  鲁欣 《天文学报》2004,45(1):16-24
利用原子数据模拟程序RCN／RCG、AUTOSTRUCTURE(AS)、GRASP分别对类氖铁的离子结构进行计算，计算过程包含了对波函数的相对论修正，计算结果包括电偶级光谱跃迁的能级间隔，谐振子强度，跃迁几率，并与实验值进行了比较，分析了3种原子数据模拟程序在计算原子结构上的精确度．  相似文献   

3.
Absolute transition probabilities have been measured for lines originating from the 5d96d and 5d97s electronic configurations in the spectrum of singly ionized gold (Au  ii ). The laser-induced breakdown spectroscopy has been applied to free gold atoms and ions produced by laser ablation. Absolute transition probabilities have been determined using the branching fraction and the Boltzmann plot methods. Theoretical branching fractions as well as radiative lifetime values have also been obtained by a relativistic Hartree–Fock method taking core polarization and configuration interaction effects into account. The new results are compared with previous results when available.  相似文献   

4.
The theory of Anstee &38; O'Mara is extended to the line broadening of transitions of singly ionized atoms by collisions with neutral hydrogen atoms. The theory is used to calculate broadening cross-sections for strong lines of singly ionized calcium, magnesium and barium. The broadening cross-sections calculated are compared with both theoretical and empirical results of other workers.  相似文献   

5.
We have studied the kinematics of the ionized gas in the nearly face-on galaxy NGC 3938 by means of observations made with theFabry–Perot interferometer TAURUS II at the William Herschel Telescope, using the Hα line. We have been able to produce high-resolution velocity and velocity-dispersion maps which allow us to make a detailed study of the kinematics of the ionized gas. In particular we have found that the vertical velocity dispersion is constant with galactocentric radius, as has already been found for the atomic and molecular gas in this galaxy. This suggests the existence of several heating mechanisms in the disc acting simultaneously to produce the observed behaviour. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

6.
Radiative lifetimes of 17 excited levels in Zr  i , in the energy interval 29 000–40 974 cm−1, have been investigated using the time-resolved laser-induced fluorescence method. The levels belong to the 4d25s5p, 4d35p and 4d5s25p electronic configurations and were excited in a single-step process from either the ground term, 4d25s2 a 3F, or from the low-lying 4d25s2 a 3P and a 5F terms. For three levels, we confirm previous measurements while for 14 of the levels the lifetimes have been measured for the first time. The experimental results are compared to theoretical calculations performed with a multiconfiguration relativistic Hartree–Fock method including core-polarization effects. Theoretical transition probabilities of astrophysical interest, scaled by the experimental lifetimes, for the depopulating channels of the investigated levels are also presented.  相似文献   

7.
The magnetic-dipole probabilities for the 1D2–3P2 and 1D2–3P1 transitions in carbon-like and oxygen-like ions are calculated up to atomic number Z =12, including relativistic corrections to the magnetic dipole operator. The ratio of the probabilities for these two transitions is found to change by up to 5 per cent compared with previous theoretical work, none of which included these relativistic corrections, with the effect being largest for the near neutral ions. The transition probability ratio for the [O  iii ] 5007 and 4959 Å lines is found to be 3.01, implying an intensity ratio of 2.98, in significantly better agreement with the observed ratio than the earlier theoretical work.  相似文献   

8.
In a previous paper by the present authors the theory of Anstee and O'Mara for the broadening of spectral lines of neutral atoms by collisions with hydrogen atoms was extended to singly ionized atoms. In this paper we apply the method to the resonance and triplet lines of ionized strontium, the infrared triplet of ionized barium, and the resonance lines of ionized beryllium. Analysis of five lines of ionized strontium, previously regarded as too strong for an abundance analysis, and two lines of neutral strontium results in a solar abundance of strontium of log( N Sr N H)+12=2.92±0.05, which is entirely consistent with the meteoritic value.  相似文献   

9.
A new calculation of photoionization cross-sections is described for the ground and excited states of atomic helium up to principal quantum number n =25 and angular momentum quantum number l =5. These cross-sections are used to calculate total recombination and cooling coefficients for atomic helium for electron temperatures given by log( T )=1(0.2)4.4. A comparison of the threshold photoionization cross-sections obtained here with extrapolations of the highly accurate bound–bound oscillator strength calculations by Drake shows that the new calculations are in error by no more than 1 per cent. The accuracy of the photoionization cross-sections used by previous workers to derive recombination coefficients is also discussed.  相似文献   

10.
The difficulties encountered in attempts to study the spectra of very late stars inspired us to prepare this spectral atlas containing essentially spectral features of M7III stars in the optical spectral region. As representative star we took the cool component of the binary symbiotic CH Cygni during one of its quiescent phases. Total number of 920 atomic lines and molecular bands have been identified with different degrees of reliability. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

11.
Radiative lifetime measurements were performed with time-resolved laser-induced fluorescence techniques for 24 levels of Nd  ii in the energy range 20 500–32 500 cm−1. For 17 levels, no previous experimental data exist. These results have allowed the testing of new theoretical calculations with the relativistic Hartree–Fock method taking configuration interactions and core-polarization effects into account, and a satisfying agreement has been found for this complex ion. A new set of calculated oscillator strengths, accurate within a few per cent for the strongest transitions, is presented for 107 lines of astrophysical interest appearing in the wavelength range 358.0–1100.0 nm. These results will be useful to evaluate abundance values of neodymium in chemically peculiar stars in relation with cosmochronology.  相似文献   

12.
The relative intensities of the most prominent extreme-ultraviolet lines of Fe  ix , seen in the outer atmospheres of the Sun and other stars, have been shown to be inconsistent with the best available atomic data. The density-sensitive Fe  ix λ 241.7/ λ 244.9 line intensity ratio, for example, yields electron densities in the solar corona that disagree with those obtained from ratios in other ions, particularly at higher densities. We show here that these differences can be largely removed by using newly calculated atomic data, in particular electron impact collision strengths that include pronounced resonance features, and by incorporating a measure of line excitation by collisional excitation and cascading.  相似文献   

13.
We present a new analysis of the main empirical calibrators of oxygen abundance for ionized gas nebulae. With that aim we have compiled an extensive sample of objects with emission-line data including the near-infrared [S  iii ] lines and the weak auroral lines which allow for the determination of the gas electron temperature. For all the objects the oxygen abundances have been derived in a homogenous way, using the most recent sets of atomic coefficients and taking into the account the effect of particle density on the temperature of O+. The residuals between directly and empirically derived abundances as a function of abundance have been studied. A grid of photoionization models, covering the range of physical properties of the gas, has been used to explain the origin of the uncertainties affecting each abundance calibrator. The range of validity for each abundance parameter has been identified and its average uncertainty has been quantified.  相似文献   

14.
Fine-structure collision strengths are calculated for transitions between the ground-state levels of atomic oxygen. The R -matrix method is used in which the (2p4) 3P, 1D and 1S terms are included as well as three pseudo-states chosen to represent the dipole polarizability of the 3P ground state. Very sophisticated configuration–interaction wavefunctions are used for the target states and a recoupling transformation to pair coupling is applied to the inner-region Hamiltonian matrix, with the 3P fine-structure energy levels being adjusted to match the observed splitting prior to diagonalization. Effective collision strengths are obtained by integrating over a Maxwellian distribution and the rate coefficient of the cooling of electron gas is determined. The cooling rates are significantly lower than those currently available, in confirmation of the result deduced from measurements of the Earth's ionosphere electron gas.  相似文献   

15.
Radiative lifetimes of nine odd levels in Hf III (5d6p z3P0,1, z1D2, z3D1,2,3, z3F2,3,4) and of two odd levels in Hf I (5d6s26p z3D2,3) have been determined using Time-Resolved Laser-Induced Fluorescence. The investigated levels in Hf I were excited in a single-step process from the ground term (5d26s2 a3F), whereas in Hf III we started from either the ground term 5d2 a3F or the low-lying 5d6s a3D term. For all of the investigated levels, the lifetimes have been measured for the first time. A multiconfiguration relativistic Hartree–Fock method, including core-polarization effects, has been used to compute radiative lifetimes of 15 Hf III levels, including those measured in this work. Transition probabilities for 55 transitions in Hf III are also given.  相似文献   

16.
The core of planetary nebula NGC 6302 is filled with high-excitation photoionized gas at low expansion velocities. It represents a unique astrophysical situation in which to search for hyperfine structure (HFS) in coronal emission lines from highly ionized species. HFS is otherwise blended by thermal or velocity broadening. Spectra containing  [Al  vi ] 3.66 μm 3P2←3P1  , obtained with Phoenix on Gemini South at resolving powers of up to 75 000, resolve the line into five hyperfine components separated by 20–60 km s−1 as a result of the coupling of the   I = 5/2  nuclear spin of 27Al with the total electronic angular momentum J . The isotope 26Al has a different nuclear spin of   I = 5  , and a different HFS, which allows us to place a 3σ upper limit on the 26Al/27Al abundance ratio of 1/33. We measure the HFS magnetic dipole coupling constants for [Al  vi ], and provide the first estimates of the electric quadrupole HFS coupling constants obtained through astronomical observations of an atomic transition.  相似文献   

17.
Electric and magnetic multipole transitions among low-lying states of doubly ionized vanadium were computed using the multi-configuration Hartree-Fock (MCHF) method with Breit-Pauli (BP) corrections to a non-relativistic Hamiltonian. Energy levels were determined up to and including 3d 2(1 G)4s b 2 G 7/2 and computed energies were found to be in good agreement with experiment and other theories. In addition to Einstein A ki coefficients for some E2 and M1 transitions, lifetime data and selected weighted oscillator strengths are also reported.  相似文献   

18.
Charge‐transfer is the main process linking neutrals and charged particles in the interaction regions of neutral (or partly ionized) gas with a plasma. In this paper we illustrate the importance of charge‐transfer with respect to the dynamics and the structure of neutral gas‐plasma interfaces. We consider the following phenomena: (1) the heliospheric interface ‐ region where the solar wind plasma interacts with the partly‐ionized local interstellar medium (LISM) and (2) neutral interstellar clouds embedded in a hot, tenuous plasma such as the million degree gas that fills the so‐called “Local Bubble”. In (1), we discuss several effects in the outer heliosphere caused by charge exchange of interstellar neutral atoms and plasma protons. In (2) we describe the role of charge exchange in the formation of a transition region between the cloud and the surrounding plasma based on a two‐component model of the cloud‐plasma interaction. In the model the cloud consists of relatively cold and dense atomic hydrogen gas, surrounded by hot, low density, fully ionized plasma. We discuss the structure of the cloud‐plasma interface and the effect of charge exchange on the lifetime of interstellar clouds. Charge transfer between neutral atoms and minor ions in the plasma produces X‐ray emission. Assuming standard abundances of minor ions in the hot gas surrounding the cold interstellar cloud, we estimate the X‐ray emissivity consecutive to the charge transfer reactions. Our model shows that the charge‐transfer X‐ray emission from the neutral cloud‐plasma interface may be comparable to the diffuse thermal X‐ray emission from the million degree gas cavity itself (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

19.
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20.
The radiation temperature–redshift relation for Friedmann–Robertson–Walker geometries is rediscussed in connection with recent observational data based on the fine-structure splitting of atomic and singly ionized carbon lines in quasar absorption-line systems. Indirect measurement of T ( z ) is one of the most powerful cosmological tests available because it may exclude even the presence of a cosmological constant. Unlike recent claims, we argue that the temperature at high z may be smaller than the standard prediction, thereby opening a window to alternative (big bang) models. By including new ingredients like a phenomenological decaying vacuum energy density and gravitational 'adiabatic' photon creation as well as late inflationary models driven by a scalar field, a new temperature law is deduced and its predictions are compared with the standard result.  相似文献   

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