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1.
We continue a systematic study of chemical abundances of the strontium filament found in the ejecta of η Carinae. To this end we interpret the emission spectrum of Sc  ii and Cr  ii using multilevel non-local thermodynamic equilibrium models. Since the atomic data for these ions were previously unavailable, we carry out ab initio calculations of radiative transition rates and electron impact excitation rate coefficients. The observed spectrum is consistent with an electron density of the order of 107 cm−3 and a temperature between 6000 and 7000 K, conditions previously determined from [Ni  ii ], [Ti  ii ] and [Sr  ii ] diagnostics. The observed spectrum indicates an abundance of Sc relative to Ni more than 40 times the solar value, while the Cr/Ni abundance ratio is roughly solar. Various scenarios of depletion and dust destruction are suggested to explain such abnormal abundances.  相似文献   

2.
According to the theory of spectral line formation in the state of non-local thermodynamic equilibrium and by using the software package FAC for the relativistic multi-configuration atomic processes, the X-ray and EUV spectra of Be-like oxygen ions are simulated. The effects of indirect processes on the X-ray and EUV spectra of Be-like O ions are probed. In the situation of the typical cosmical plasma density (ne = 1010/cm3), three models are adopted. For different temperatures, the processes of formation of X-ray and EUV spectra are simulated, and the contributions of indirect processes to the formation of spectral lines are analyzed and compared. Besides, their rate coefficients are given. It is found that in the process of spectral line formation, the indirect processes have exceedingly important effects.  相似文献   

3.
New, more detailed calculations of the emission spectra of the He-like Kα complex of calcium, iron and nickel have been carried out using data from both distorted-wave and R-matrix calculations. The value of the GD ratio (an extended definition of the G ratio that accounts for the effect of resolved and unresolved satellite lines) is significantly enhanced at temperatures below the temperature of He-like maximum abundance. Furthermore, it is shown that satellite lines are important contributors to the GD ratio such that   GD / G > 1  at temperatures well above the temperature of maximum abundance. These new calculations demonstrate, with an improved treatment of the KLn     satellite lines, that Kα satellite lines need to be included in models of He-like spectra even at relatively high temperatures. The excellent agreement between spectra and line ratios calculated from R-matrix and distorted-wave data also confirms the validity of models based on distorted-wave data for highly charged systems, provided the effect of resonances is taken into account as independent processes.  相似文献   

4.
We study the nature of the [Ti  ii ] and [Ni  ii ] emission from the so-called strontium filament found in the ejecta of η Carinae. To this purpose, we employ multilevel models of the Ti  ii and Ni  ii systems, which are used to investigate the physical condition of the filament and the excitation mechanisms of the observed lines. For the Ti  ii ion, for which no atomic data were previously available, we carry out ab initio calculations of radiative transition rates and electron impact excitation rate coefficients. It is found that the observed spectrum is consistent with the lines being excited in a mostly neutral region with an electron density of the order of 107 cm−3 and a temperature around 6000 K. In analysing three observations with different slit orientations recorded between 2000 March and 2001 November, we find line ratios that change among various observations, in a way consistent with changes of up to an order of magnitude in the strength of the continuum radiation field. These changes result from different samplings of the extended filament due to the different slit orientations used for each observation, and yield clues on the spatial extent and optical depth of the filament. The observed emission indicates a large Ti/Ni abundance ratio relative to solar abundances. It is suggested that the observed high Ti/Ni ratio in gas is caused by dust–gas fractionation processes and does not reflect the absolute Ti/Ni ratio in the ejecta of η Carinae. We study the condensation chemistry of Ti, Ni and Fe within the filament and suggest that the observed gas phase overabundance of Ti is likely the result of selective photoevaporation of Ti-bearing grains. Some mechanisms for such a scenario are proposed.  相似文献   

5.
The solar photospheric abundance of ruthenium is revised on the basis of a new set of oscillator strengths derived for Ru  i transitions with wavelengths in the spectral range 2250–4710 Å. The new abundance value (in the usual logarithmic scale where the solar hydrogen abundance is equal to 12.00),   A Ru= 1.72 ± 0.10  , is in agreement with the most recent meteoritic result,   A Ru= 1.76 ± 0.03  . The accuracy of the transition probabilities, obtained using a relativistic Hartree–Fock model including core-polarization effects, has been assessed by comparing the theoretical lifetimes with previous experimental results. A comparison is also made with new measurements performed in this work by the time-resolved laser-induced fluorescence spectroscopy for 10 highly excited odd-parity levels of Ru  i .  相似文献   

6.
时间和频率技术新进展   总被引：5，自引：0，他引：5  
张昱  翟造成 《天文学进展》1997,15(4):285-292
概述了最近几年时间和频率技术的最新进展，给出了各种实用的原子频率标准的最新发展以及它们的性能指标的最新结果，介绍了国际原子时的归算方法和所达到的新水平，并对各种原子钟在归算子中的应用概况和所起的作用进行了比较，强调了氢原子钟的特殊作用和地位，同时也综述了高精度的时间同步和时频计量新技术的进展，特别是对为提高ＧＰＳ这一国际时间同步辐射技术的应用水平进行的各种实验研究工作的最新进展作了进行描述，对目前  相似文献   

7.
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8.
Recent advances in modelling the radiating character of dynamic laboratory and astrophysical plasmas are applied here in a new examination of the properties of the atmosphere of the classical T Tauri star BP Tau. We analyse archived International Ultraviolet Explorer ( IUE ) UV spectra of BP Tau. We adopt a collisional-radiative model and utilize emission measure (EM) and differential emission measure (DEM) techniques to try to constrain the distribution of emitting material in temperature in the atmosphere of this star. We use spectroscopic diagnostic techniques to probe atmospheric parameters such as electron density, and to set constraints on the volume of emission regions. This work is important for understanding the fundamental properties of BP Tau and other T Tauri stars, and for providing a more complete basis for models of their atmospheres.  相似文献   

9.
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10.
梁雅琼  仲佳勇 《天文学报》2005,46(2):151-157
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．  相似文献   

11.
Atomic models developed by the author and used to interpret the spectra of cool shells from old classical novae are reviewed. Some of the remaining problems relating to the spectra are discussed briefly. The use of these data in photoionization models is described, and the evolution of nova shells is discussed.  相似文献   

12.
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   

13.
The lifetimes of three short-lived levels belonging to the 4f96p configuration and of two long-lived levels of the 4f95d configuration of Dy  iii have been measured for the first time using time-resolved laser-induced fluorescence techniques. They are in good agreement with theoretical values calculated within the framework of a pseudo-relativistic configuration interaction approximation. Using the experimental lifetimes and the theoretical branching fractions, a first set of transition probabilities of astrophysical interest has been obtained for Dy  iii .  相似文献   

14.
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   

15.
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16.
Using three independent theoretical approaches (CA, HFR + CP, AUTOSTRUCTURE), oscillator strengths have been calculated for a set of Tc  ii transitions of astrophysical interest and the reliability of their absolute scale has been assessed. The examination of the spectra emitted by some Ap stars has allowed the identification of Tc  ii transitions in HD 125248. This Tc  ii detection should however await confirmation from spectral synthesis relying on dedicated model atmospheres. New partition functions are also provided for Tc  i , Tc  ii and Tc  iii for temperatures ranging between 4000 and 13 000 K.  相似文献   

17.
We study the nature of the peculiar [Sr  ii ] and Sr  ii emission filament found in the ejecta of Eta Carinae. To this purpose we carry out ab initio calculations of radiative transition probabilities and electron impact excitation rate coefficients for Sr  ii . Then we build a multilevel model for the system which is used to investigate the physical condition of the filament and the nature of the observed allowed and forbidden Sr  ii optical emission. It is found that the observed spectrum is consistent with the lines being pumped by the continuum radiation field in a mostly neutral region with electron density near 107 cm−3. Under these conditions, the observed emission can be explained without the need for a large Sr overabundance.  相似文献   

18.
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   

19.
Effective collision strengths for electron-impact excitation of the N-like ion Ne  iv are calculated in the close-coupling approximation using the multichannel R-matrix method. Specific attention is given to the 10 astrophysically important fine-structure forbidden transitions among the 4So, 2Do and 2Po levels in the 2s22p3 ground-state configuration. The expansion of the total wavefunction incorporates the lowest 11 LS eigenstates of Ne  iv , consisting of eight n  = 2 terms with configurations 2s22p3, 2s2p4 and 2p5, together with three n  = 3 states of configuration 2s22p23s. We present in graphical form the effective collision strengths obtained by thermally averaging the collision strengths over a Maxwellian distribution of velocities, for all 10 fine-structure transitions, over the range of electron temperatures log T (K) = 3.6 to log T (K) = 6.1 (the range appropriate for astrophysical applications). Comparisons are made with the earlier, less sophisticated close-coupling calculation of Giles, and excellent agreement is found in the limited temperature region where a comparison is possible [log T (K) = 3.7 to log T (K) = 4.3]. At higher temperatures the present data are the only reliable results currently available.  相似文献   

20.
Effective collision strengths for electron-impact excitation of the N-like ion S  x are calculated in the close-coupling approximation using the multichannel R -matrix method. Specific attention is given to the 10 astrophysically important fine-structure forbidden transitions among the 4So, 2Do and 2Po levels in the 2s22p3 ground configuration. The total (e−+ion) wavefunction is expanded in terms of the 11 lowest LS eigenstates of S  x , and each eigenstate is represented by extensive configuration-interaction wavefunctions. The collision strengths obtained are thermally averaged over a Maxwellian distribution of velocities, for all 10 fine-structure transitions, over the range of electron temperatures log  T (K)=4.6–6.7 (the range appropriate for astrophysical applications). The present effective collision strengths are the only results currently available for these fine-structure transition rates.  相似文献   

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