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1.
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
2.
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
3.
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
4.
Alan Hibbert Tomas Brage Janine Fleming 《Monthly notices of the Royal Astronomical Society》2002,333(4):885-893
We use both the civ3 and mchf codes to calculate oscillator strengths of allowed and intercombination lines in the 3s2 3p–3s3p2 multiplets. Valence, core–valence and some core–core correlation effects are included. The two approaches give results in excellent agreement. Core effects are particularly important for the intercombination lines, though relatively minor for allowed transitions.
We obtain a branching ratio of 1.42 with an estimated accuracy of 0.02 for the transitions, compared with an experimental value of 1.12±0.1 . The A -values of the intercombination lines are substantially different from those of previous calculations. 相似文献
We obtain a branching ratio of 1.42 with an estimated accuracy of 0.02 for the transitions, compared with an experimental value of 1.12±0.1 . The A -values of the intercombination lines are substantially different from those of previous calculations. 相似文献
5.
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 ) 3 P, 1 D and 1 S terms are included as well as three pseudo-states chosen to represent the dipole polarizability of the 3 P 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 3 P 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
6.
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
7.
Elodie A. Engel Natasha Doss Gregory J. Harris Jonathan Tennyson 《Monthly notices of the Royal Astronomical Society》2005,357(2):471-477
The wavelength and Einstein A coefficient are calculated for all rotation–vibration transitions of 4 He1 H+ , 3 He1 H+ , 4 He2 H+ and 3 He2 H+ , giving a complete line list and the partition function for 4 HeH+ and its isotopologues. This opacity is included in the calculation of the total opacity of low-metallicity stars and its effect is analysed for different conditions of temperature, density and hydrogen number fraction. For a low helium number fraction (as in the Sun), it is found that HeH+ has a visible but small effect for very low densities (ρ≤ 10−10 g cm−3 ) , at temperatures around 3500 K. However, for high helium number fraction, the effect of HeH+ becomes important for higher densities (ρ≤ 10−6 g cm−3 ) , its effect being most important for a temperature around 3500 K. Synthetic spectra for a variety of different conditions are presented. 相似文献
8.
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
9.
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
10.
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
11.
The rates of rotational transitions for HCO+ , the most abundant ion in interstellar space, induced by collision with helium are obtained for temperatures ranging from 10 to 80 K. The calculations are based on a new potential energy surface for the He–HCO+ interaction and on a scattering matrix whose accuracy was checked by pressure broadening and shift measurements. The rates decrease for increasing values of j and Δ j , with a temperature trend depending on the energy involved in the transitions: if it is small, the rates are almost constant, while an increase with T is found for other cases. Comparison with previous and less accurate results shows an agreement within 50 per cent. Comparison between state-to-state and pressure broadening cross-sections allows us to discuss importance and influence of elastic and inelastic collisions. 相似文献
12.
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
13.
We have used the Ultra-High-Resolution Facility (UHRF) at the AAT, operating at a resolution of 0.35 km s−1 (FWHM), to observe K i and C2 absorption lines arising in the circumstellar environment of the post-AGB star HD 56126. We find three narrow circumstellar absorption components in K i , two of which are also present in C2 . We attribute this velocity structure to discrete shells resulting from multiple mass-loss events from the star. The very high spectral resolution has enabled us to resolve the intrinsic linewidths of these narrow lines for the first time, and we obtain velocity dispersions ( b -values) of 0.2–0.3 km s−1 for the K i components, and 0.54±0.03 km s−1 for the strongest (and best defined) C2 component. These correspond to rigorous kinetic temperature upper limits of 211 K for K i and 420 K for C2 , although the b -value ratio implies that these two species do not co-exist spatially. The observed degree of rotational excitation of C2 implies low kinetic temperatures ( T k ≈10 K) and high densities ( n ≈106 to 107 cm−3 ) within the shell responsible for the main C2 component. Given this low temperature, the line profiles then imply either mildly supersonic turbulence or an unresolved velocity gradient through the shell. 相似文献
14.
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
15.
16.
Anton Lipovka Ramona Núñez-López Vladimir Avila-Reese 《Monthly notices of the Royal Astronomical Society》2005,361(3):850-854
We report new calculations of the cooling rate of primordial gas by the HD molecule, taking into account its ro-vibrational structure. The HD cooling function is calculated including radiative and collisional transitions for J ≤ 8 rotational levels, and for the vibrational levels v = 0, 1, 2 and 3. The ro-vibrational level population is calculated from the balance equation assuming steady state. The cooling function is evaluated in the ranges of the kinetic temperatures, T k , from 102 to 2 × 104 K and the number densities, n H , from 1 to 108 cm−3 . We find that the inclusion of collisional ro-vibrational transitions increases significantly the HD cooling efficiency, in particular for high densities and temperatures. For n H ≳ 105 and T k ∼ 104 K the cooling function becomes more than an order of magnitude higher than previously reported. We give also the HD cooling rate in the presence of the cosmic microwave radiation field for radiation temperatures of 30, 85 and 276 K (redshifts of 10, 30 and 100). The tabulated cooling functions are available at http://www.cifus.uson.mx/Personal_Pages/anton/DATA/HD_cooling/HD_cool.html . We discuss the relevance to explore the effects of including our results into models and simulations of galaxy formation, especially in the regime when gas cools down from temperatures above ∼3000 K. 相似文献
17.
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
18.
We study the prospects for observing H2 emission during the assembly of primordial molecular cloud kernels. The primordial molecular cloud cores, which resemble those at the present epoch, can emerge around 1+ z ∼20 according to recent numerical simulations. The kernels form inside the cores, and the first stars will appear inside the kernels. A kernel typically contracts to form one of the first generation stars with an accretion rate that is as large as ∼0.01 M⊙ yr−1 . This occurs owing to the primordial abundances, which result in a kernel temperature of order 1000 K, and the collapsing kernel emits H2 line radiation at a rate ∼1035 erg s−1 . Predominantly J =5-3 ( v =0) rotational emission of H2 is expected. At redshift 1+ z ∼20 , the expected flux is ∼0.01 μJy for a single kernel. While an individual object is not observable by any facilities available in the near future, the expected assembly of primordial star clusters on subgalactic scales can result in fluxes at the sub-mJy level. This is marginally observable with ASTRO-F and ALMA. We also examine the rotational J =2-0 ( v =0) and vibrational δv =1 emission lines. The former may possibly be detectable with ALMA. 相似文献
19.
Cesare Cecchi-Pestellini Alexander Dalgarno 《Monthly notices of the Royal Astronomical Society》2000,313(1):L6-L8
A model is constructed of the material in front of the star Cygnus OB2 no. 12 in which dense cores are embedded in diffuse clumps of gas. The model reproduces the measured abundances of C2 and CO, and predicts a column density of 91010 cm2 for HCO+ . 相似文献
20.
Itziar Aretxaga † S. Benetti R. J. Terlevich ‡ A. C. Fabian E. Cappellaro M. Turatto M. Della Valle 《Monthly notices of the Royal Astronomical Society》1999,309(2):343-354
We present a spectro-photometric catalogue of the evolution of supernova 1988Z, which combines new and published observations in the radio, optical and X-ray bands, with the aim of offering a comprehensive view of the evolution of this object and deriving the total energy radiated since its discovery. The major contribution to the total radiated energy comes at optical to X-ray frequencies, with a total emission of at least 2×1051 erg (for H0 =50 km s−1 Mpc−1 ) in 8.5 yr. A model-dependent extrapolation of this value indicates that the total radiated energy may be as high as 1052 erg. The high value of the radiated energy supports a scenario in which most of the kinetic energy of the ejecta is thermalized and radiated in a short interaction with a dense circumstellar medium of nearly constant density. In this sense, 1988Z is not a supernova but a young and compact supernova remnant. 相似文献