共查询到20条相似文献,搜索用时 105 毫秒
1.
G. Malcheva R. Mayo M. Ortiz J. Ruiz L. Engström H. Lundberg H. Nilsson P. Quinet É. Biémont K. Blagoev 《Monthly notices of the Royal Astronomical Society》2009,395(3):1523-1528
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 4d2 5s5p, 4d3 5p and 4d5s2 5p electronic configurations and were excited in a single-step process from either the ground term, 4d2 5s2 a 3 F, or from the low-lying 4d2 5s2 a 3 P and a 5 F 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
2.
A. Alonso-Medina C. Colón A. Zanón 《Monthly notices of the Royal Astronomical Society》2009,395(1):567-579
Transition probabilities and oscillator strengths of 382 lines with astrophysical interest arising from 5d9 6s2 6p, 5d10 6s n l, 5d10 6s2 , 5d10 6p2 , 5d10 6p7s and 5d10 6p6d configurations and some levels radiative lifetimes of Pb iii have been calculated. These values were obtained in intermediate coupling (IC) and using relativistic Hartree–Fock calculations including core-polarization effects. We use for the IC calculations the standard method of least-square fitting from experimental energy levels by means of Cowan computer code. The inclusion in these calculations of the 5d10 6p7s and 5d10 6p6d configurations has facilitated us a complete assignment of the levels of energy in the Pb iii . Transition probabilities, oscillator strengths and radiative lifetimes obtained are generally in good agreement with the experimental data. 相似文献
3.
J. Campos M. Ortiz R. Mayo E. Biémont † P. Quinet K. Blagoev G. Malcheva 《Monthly notices of the Royal Astronomical Society》2005,363(3):905-910
Radiative parameters for transitions depopulating the levels belonging to the 4d8 5s2 , 4d9 6s and 4d9 5d configurations of Ag ii have been obtained from a combination of theoretical lifetimes and experimental branching fractions. On the experimental side, a laser-produced plasma was used as a source of Ag+ ions. The light emitted by the plasma was analysed by a grating monochromator coupled with a time-resolved optical multichannel analyser system. Spectral response calibration of the experimental system was performed using a deuterium lamp in the wavelength range from 200 to 400 nm, and a standard tungsten lamp in the range from 350 to 600 nm. The transition probabilities were obtained from measured branching ratios and theoretical radiative lifetimes of the corresponding states calculated with a relativistic Hartree–Fock approach including core-polarization effects and configuration interaction in an extensive way. Theoretical and experimental data have been compared and the new data have also been compared with the few previous results available in the literature. 相似文献
4.
The neighbouring lines a 6 D5/2 – x 6 Po 3/2 (1272.617 Å) and a 6 D5/2 – w 2 Po 3/2 (1272.657 Å) have been observed in the UV spectrum of χ Lupi to be of comparable intensity. The latter, Δ S = 2, transition would be expected to be very weak. The two upper states should display negligible mixing. We give a detailed, quantitative discussion of how the two upper states are in fact strongly mixed through their mixing with 3d6 (3 D)4p 4 Po 3/2 , and hence we explain the relative strengths of the two UV lines. 相似文献
5.
F. P. Keenan D. B. Jess K. M. Aggarwal R. J. Thomas J. W. Brosius J. M. Davila 《Monthly notices of the Royal Astronomical Society》2007,376(1):205-214
Recent fully relativistic calculations of radiative rates and electron impact excitation cross-sections for Fe xiii are used to generate emission-line ratios involving 3s2 3p2 –3s3p3 and 3s2 3p2 –3s2 3p3d transitions in the 170–225 and 235–450 Å wavelength ranges covered by the Solar Extreme-Ultraviolet Research Telescope and Spectrograph (SERTS). A comparison of these line ratios with SERTS active region observations from rocket flights in 1989 and 1995 reveals generally very good agreement between theory and experiment. Several new Fe xiii emission features are identified, at wavelengths of 203.79, 259.94, 288.56 and 290.81 Å. However, major discrepancies between theory and observation remain for several Fe xiii transitions, as previously found by Landi and others, which cannot be explained by blending. Errors in the adopted atomic data appear to be the most likely explanation, in particular for transitions which have 3s2 3p3d 1 D2 as their upper level. The most useful Fe xiii electron-density diagnostics in the SERTS spectral regions are assessed, in terms of the line pairs involved being (i) apparently free of atomic physics problems and blends, (ii) close in wavelength to reduce the effects of possible errors in the instrumental intensity calibration, and (iii) very sensitive to changes in N e over the range 108 –1011 cm−3 . It is concluded that the ratios which best satisfy these conditions are 200.03/202.04 and 203.17/202.04 for the 170–225 Å wavelength region, and 348.18/320.80, 348.18/368.16, 359.64/348.18 and 359.83/368.16 for 235–450 Å. 相似文献
6.
C. A. Ramsbottom K. L. Bell F. P. Keenan 《Monthly notices of the Royal Astronomical Society》1999,307(3):669-676
Effective collision strengths for the 10 astrophysically important fine-structure forbidden transitions among the 4 So , 2 Do and 2 Po levels in the 3s2 3p3 configuration of Cl iii are presented. The calculation employs the multichannel R-matrix method to compute the electron-impact excitation collision strengths in a close-coupling expansion, which incorporates the lowest 23 LS target eigenstates of Cl iii . These states are formed from the 3s2 3p3 , 3s3p4 , 3s2 3p2 3d and 3s2 3p2 4s configurations. The Maxwellian-averaged effective collision strengths are presented graphically for all 10 fine-structure transitions over a wide range of electron temperatures appropriate for astrophysical applications [log T (K)=3.3−log T (K)=5.9]. Comparisons are made with the earlier seven-state close-coupling calculation of Butler & Zeippen, and in general excellent agreement is found in the low-temperature region where a comparison is possible [log T (K)=3.3−log T (K)=4.7]. However, discrepancies of up to 30 per cent are found to occur for the forbidden transitions which involve the 4 So ground state level, particularly for the lowest temperatures considered. At the higher temperatures, the present data are the only reliable results currently available. 相似文献
7.
E. Olalla N. J. Wilson K. L. Bell I. Martin A. Hibbert 《Monthly notices of the Royal Astronomical Society》2002,332(4):1005-1008
A 25-state R -matrix calculation is performed to obtain photoionization cross-sections for transitions from the 1s2 2s2 2p2 3 P ground state of the O iii ion. Results are obtained for a range of photon energies, including those at which K-shell photoionization processes take place. We compare our results with those from previous calculations. Excellent agreement is obtained. We also consider resonances owing to transitions of a 1s electron excited into the 2p orbital and compare with a recent calculation. 相似文献
8.
É. Biémont K. Blagoev V. Fivet G. Malcheva R. Mayo M. Ortiz P. Quinet 《Monthly notices of the Royal Astronomical Society》2007,380(4):1581-1588
Absolute transition probabilities have been measured for lines originating from the 5d9 6d and 5d9 7s 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
9.
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 4 So , 2 Do and 2 Po levels in the 2s2 2p3 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 2s2 2p3 , 2s2p4 and 2p5 , together with three n = 3 states of configuration 2s2 2p2 3s. 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
10.
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 4 So , 2 Do and 2 Po levels in the 2s2 2p3 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
11.
F.P. Keenan K.M. Aggarwal D.R. Williams M. Mathioudakis K.J.H. Phillips 《Monthly notices of the Royal Astronomical Society》2001,326(4):1387-1390
Recent R -matrix calculations of electron impact excitation rates for transitions among the 2s2 2p2 , 2s2p3 and 2p4 levels of Fe xxi are used to derive theoretical electron density ( N e ) sensitive emission-line ratios involving 2s2 2p2 –2s2p3 transitions in the ∼98–146Å wavelength range. A comparison of these with observations from the PLT tokamak plasma, for which the electron density has been independently determined, reveals generally very good agreement between theory and experiment, and in some instances removes discrepancies found previously. The observed Fe xxi ratios for a solar flare, obtained with the OSO–5 satellite, imply electron densities which are consistent, with discrepancies that do not exceed 0.2 dex. In addition, the derived values of N e are similar to those estimated for the high-temperature regions of other solar flares. The good agreement between theory and observation, in particular for the tokamak spectra, provides experimental support for the accuracy of the present line-ratio calculations, and hence for the atomic data on which they are based. 相似文献
12.
Z. G. Zhang S. Svanberg P. Palmeri P. Quinet E. Biémont 《Monthly notices of the Royal Astronomical Society》2002,334(1):1-10
The lifetimes of three short-lived levels belonging to the 4f9 6p configuration and of two long-lived levels of the 4f9 5d 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
13.
The magnetic-dipole probabilities for the 1 D2 –3 P2 and 1 D2 –3 P1 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
14.
We present the excitation energies and lifetimes for the 3 s 3 p 3 d 4 F 7/2,9/2 levels for five aluminium-like ions of the iron group. Apart from the wavelengths, this also includes the transition probabilities and branching ratios for the electric-dipole allowed (E1) and forbidden (M1, E2, M2) lines into the energetically lower lying levels of the 3 s 2 3 d , 3 s 3 p 2 and 3 s 3 p 3 d configurations. Applying systematically enlarged multiconfiguration Dirac–Fock (MCDF) wavefunctions, here the effects of relativity and the electron–electron correlation are treated within the same (computational) model. 相似文献
15.
F. P. Keenan B. R. Espey M. Mathioudakis K. M. Aggarwal F. L. Crawford W. A. Feibelman F. C. McKenna 《Monthly notices of the Royal Astronomical Society》1999,309(1):195-198
An inspection of a GHRS/ HST spectrum of the symbiotic star RR Telescopii reveals the presence of the [Al ii ] 3s2 1 S – 3s3p 3 P2 line at a vacuum wavelength of 2661.06±0.08 Å, 8.89±0.08 Å away from the Al ii ] 3s2 1 S – 3s3p 3 P1 intercombination transition at 2669.95 Å, in good agreement with the theoretical prediction of Δ λ =8.80 Å. We also find that the Al ii ] line profile is asymmetric, showing a strong low-density component with a weak high-density wing, redshifted by 30 km s−1 , in agreement with the findings of Schild & Schmid, which were based on optical observations. Our measurement of the emission-line ratio R I (2661.06 Å)/ I (2669.95 Å)=0.027±0.003 implies log N e =5.8±0.2, in good agreement with the densities found from other ions, such as Si iii . These results provide strong evidence that we have detected the [Al ii ] line, the first time (to our knowledge) that this feature has been reliably identified in an astrophysical or laboratory spectrum. 相似文献
16.
R. C. North T. R. Marsh C. K. J. Moran U. Kolb R. C. Smith R. Stehle 《Monthly notices of the Royal Astronomical Society》2000,313(2):383-391
We have discovered that the spectrum of the well-known dwarf nova EM Cyg is contaminated by light from a K25V star (in addition to the K-type mass donor star). The K25V star contributes approximately 16 per cent of the light from the system and if not taken into account has a considerable effect upon radial velocity measurements of the mass donor star. We obtain a new radial velocity amplitude for the mass donor star of K 2 =202±3 km s1 , compared with the value of K 2 =135±3 km s1 obtained in Stover, Robinson & Nather's classic study of EM Cyg. The revised value of the amplitude, combined with a measurement of rotational broadening of the mass donor, v sin i =140±6 km s1 , leads to a new mass ratio of q M 2 M 1 =0.88±0.05. This solves a long-standing problem with EM Cyg, because Stover et al.'s measurements indicated a mass ratio q >1, a value that should have led to dynamically unstable mass transfer for the secondary mass deduced by Stover et al. The revised value of the mass ratio, combined with the orbital inclination i =67±2°, leads to masses of 0.99±0.12 M and 1.12±0.08 M for the mass donor and white dwarf respectively. The mass donor is evolved, because it has a later spectral type (K3) than its mass would imply.
We discuss whether the K star could be physically associated with EM Cyg or not, and present the results of the spectroscopic study. 相似文献
We discuss whether the K star could be physically associated with EM Cyg or not, and present the results of the spectroscopic study. 相似文献
17.
E. Biémont D. C. Morton & P. Quinet 《Monthly notices of the Royal Astronomical Society》1998,297(3):713-731
An extensive set of oscillator strengths and transition probabilities has been obtained for the UV transitions originating from the ground 4s2 4p n ( n =1–3) states of Ge II , As II and Se II . These new data, calculated within the framework of a pseudo-relativistic Hartree–Fock (HFR) approach, fill in the gap existing in the atomic data needed for elemental abundance analysis of the interstellar medium. The f values are compared with the rather scarce results previously published in the literature. The astrophysical implications of the new transition rates regarding the interstellar medium are discussed. 相似文献
18.
The ab initio R -matrix method is used to calculate effective collision strengths for electron-impact excitation of the sulphur-like ion Cl ii in the close-coupling approximation. All 10 astrophysically important fine-structure forbidden transitions within the 3s2 3p4 , , ground configuration levels are considered. The 12 lowest LS target states are included in the calculation. Effective collision strengths are obtained by averaging the electron collision strengths over a Maxwellian distribution of electron velocities. Results are presented for electron temperatures in the range log T (K)=3.3 to log T (K)=5.5 , appropriate for astrophysical applications. These are the only effective collision strength data that are currently available. 相似文献
19.
E. Charro K. L. Bell I. Martin A. Hibbert 《Monthly notices of the Royal Astronomical Society》2000,313(2):247-251
An 11-state R -matrix calculation is performed to obtain cross-sections for the photoionization of the 1s2 2s 2 S ground states of N v and O vi . For both ions at low photon energies, corresponding solely to the 2s photoionization cross-section, excellent agreement is found with previous calculations. For higher photon energies, permitting inner-shell photoionization of the 1s electron, excellent accord is found with the recent calculation of Nahar for O vi , whilst for N v resonance structure is found which previous calculations omitted. 相似文献
20.
We have calculated oscillator strengths for the J – J ' levels of the a 6 D– z 6 Po , the a 6 D– z 6 Do and the a 6 D– z 6 Fo multiplets in Fe ii , using configuration interaction wave functions. The importance of the mixing of the 6 Po , 6 Do and 6 Fo states is shown, as is the effect of core polarization of both the 3 p and 3 s orbitals. Good agreement with recent experimental results is obtained. 相似文献