共查询到20条相似文献,搜索用时 15 毫秒
1.
V. Fivet P. Quinet P. Palmeri É. Biémont M. Asplund N. Grevesse A. J. Sauval L. Engström H. Lundberg H. Hartman H. Nilsson 《Monthly notices of the Royal Astronomical Society》2009,396(4):2124-2132
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
2.
We report the first extensive measurements of hyperfine structure in Ta ii . Spectra of Ta ii were recorded by high-resolution Fourier transform spectrometry in the region 10 000–53 000 cm-1 (1886–10 000 Å) and the majority of observed lines show significant hyperfine structure. Computer fits to several hundred of these line profiles have yielded values of the magnetic dipole hyperfine interaction constant A for 88 energy levels with an uncertainty of between 0.5 and 10 per cent for the majority of A factors. The A factors range from −0.078 to +0.065 cm−1 for the even levels and from −0.064 to +0.083 cm−1 for the odd levels. For the majority of these A factors no previous measurements are known. Approximate values of the electric quadrupole hyperfine interaction constant B were found for 73 levels. These measurements of A and B factors allow, for the first time, the effects of hyperfine structure in Ta ii lines to be correctly accounted for both in abundance analysis and in the resolution of blended lines in astrophysical spectra. 相似文献
3.
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
4.
F. P. Keenan J. J. Drake K. M. Aggarwal 《Monthly notices of the Royal Astronomical Society》2007,381(4):1727-1732
New fully relativistic calculations of radiative rates and electron impact excitation cross-sections for Fe xvi are used to determine theoretical emission-line ratios applicable to the 251–361 and 32–77 Å portions of the extreme-ultraviolet (EUV) and soft X-ray spectral regions, respectively. A comparison of the EUV results with observations from the Solar Extreme-Ultraviolet Research Telescope and Spectrograph (SERTS) reveals excellent agreement between theory and experiment. However, for emission lines in the 32–49 Å portion of the soft X-ray spectral region, there are large discrepancies between theory and measurement for both a solar flare spectrum obtained with the X-Ray Spectrometer/Spectrograph Telescope (XSST) and for observations of Capella from the Low-Energy Transmission Grating Spectrometer (LETGS) on the Chandra X-ray Observatory . These are probably due to blending in the solar flare and Capella data from both first-order lines and from shorter wavelength transitions detected in second and third order. By contrast, there is very good agreement between our theoretical results and the XSST and LETGS observations in the 50–77 Å wavelength range, contrary to previous results. In particular, there is no evidence that the Fe xvi emission from the XSST flare arises from plasma at a much higher temperature than that expected for Fe xvi in ionization equilibrium, as suggested by earlier work. 相似文献
5.
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
6.
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
7.
J. A. Rubiño-Martín J. Chluba R. A. Sunyaev 《Monthly notices of the Royal Astronomical Society》2006,371(4):1939-1952
We compute the spectral distortions of the cosmic microwave background (CMB) arising during the epoch of cosmological hydrogen recombination within the standard cosmological (concordance) model for frequencies in the range 1–3500 GHz. We follow the evolution of the populations of the hydrogen levels including states up to principle quantum number n = 30 in the redshift range 500 ≤ z ≤ 3500 . All angular momentum substates are treated individually, resulting in a total number of 465 hydrogen levels. The evolution of the matter temperature and the fraction of electrons coming from He ii are also included. We present a detailed discussion of the distortions arising from the main dipolar transitions, for example Lyman and Balmer series, as well as the emission due to the two-photon decay of the hydrogen 2s level. Furthermore, we investigate the robusteness of the results against changes in the number of shells considered. The resulting spectral distortions have a characteristic oscillatory behaviour, which might allow experimentalists to separate them from other backgrounds. The relative distortion of the spectrum exceeds a value of 10−7 at wavelengths longer than 21 cm. Our results also show the importance of detailed follow-up of the angular momentum substates, and their effect on the amplitude of the lines. The effect on the residual electron fraction is only moderate, and mainly occurs at low redshifts. The CMB angular power spectrum is changed by less than 1 per cent. Finally, our computations show that if the primordial radiation field is described by a pure blackbody, then there is no significant emission from any hydrogen transition at redshifts greater than z ∼ 2000 . This is in contrast to some earlier works, where the existence of a 'pre-recombination' peak was claimed. 相似文献
8.
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
9.
Si x emission lines in spectra obtained with the Solar EUV Rocket Telescope and Spectrograph (SERTS)
F. P. Keenan E. O'Shea R. J. Thomas J. W. Brosius A. Katsiyannis R. S. I. Ryans R. H. G. Reid A. K. Pradhan H. L. Zhang 《Monthly notices of the Royal Astronomical Society》2000,315(3):450-456
New R -matrix calculations of electron impact excitation rates for transitions among the 2s2 2p, 2s2p2 and 2p3 levels of Si x are presented. These data are subsequently used, in conjunction with recent estimates for proton excitation rates, to derive theoretical electron density sensitive emission-line ratios involving transitions in the ∼253–356 Å wavelength range. A comparision of these with observations of a solar active region and subflare, obtained during the 1989 flight of the Solar EUV Rocket Telescope and Spectrograph ( SERTS ), reveals that the electron densities determined from most of the Si x line ratios are consistent with one another for both solar features. In addition, the derived densities are also in good agreement with the values of N e estimated from diagnostic lines in other species formed at similar electron temperatures to Si x , such as Fe xii and Fe xiii . These results provide observational support for the general accuracy of the adopted atomic data, and hence line ratio calculations, employed in the present analysis. However, we find that the Si x 256.32-Å line is blended with the He ii transition at the same wavelength, while the feature at 292.25 Å is not due to Si x , but currently remains unidentified. The intensity of the 253.81-Å line in the SERTS active region spectrum is about a factor of 3 larger than expected from theory, but the reason for this is unclear, and requires additional observations to explain the discrepancy. 相似文献
10.
Ralph S. Sutherland 《Monthly notices of the Royal Astronomical Society》1998,300(2):321-330
New calculations of free–free transition matrix element integrals are performed using modern symbolic computing techniques to evaluate the hypergeometric functions with complex arguments. The results are presented in both graphical and tabular form including accurate extrapolation methods. The results are accurate to the level of ∼ 10−4 , beyond which relativistic corrections would be needed, which are not included. The results are also computed over a very wide range of scaled ionic temperature (γ2 ) and wavelength, extending earlier results to new regimes encountered in highly photoionized and non-equilibrium ionization plasmas. These results will be useful in the spectral range from submillimetre to hard X-ray wavelengths and temperatures from 10 to 109 K. 相似文献
11.
D. R. Gonçalves A. Mampaso R. L. M. Corradi C. Quireza 《Monthly notices of the Royal Astronomical Society》2009,398(4):2166-2176
We obtained optical long-slit spectra of four planetary nebulae (PNe) with low-ionization pair of knots, namely He 1-1, IC 2149, KjPn 8 and NGC 7662.
These data allow us to derive the physical parameters and excitation of the pairs of knots, and those of higher ionization inner components of the nebulae, separately.
Our results are as follows. (1) The electron temperatures of the knots are within the range 9500–14 500 K, similar to the temperatures of the higher ionization rims/shells. (2) Typical knots' densities are 500–2000 cm−3 . (3) Empirical densities of the inner rims/shells are higher than those of the pairs of knots, by up to a factor of 10. Theoretical predictions, at variance with the empirical results, suggest that knots should be denser than the inner regions, by at least a factor of 10. (4) Empirical and theoretical density contrasts can be reconciled if we assume that at least 90 per cent of the knots' gas is neutral (likely composed of dust and molecules). (5) By using the new Raga et al. shock modelling and diagnostic diagrams appropriated for spatially resolved PNe, we suggest that high-velocity shocked knots travelling in the photoionized outer regions of PNe can explain the emission of the pairs of knots analysed in this paper. 相似文献
These data allow us to derive the physical parameters and excitation of the pairs of knots, and those of higher ionization inner components of the nebulae, separately.
Our results are as follows. (1) The electron temperatures of the knots are within the range 9500–14 500 K, similar to the temperatures of the higher ionization rims/shells. (2) Typical knots' densities are 500–2000 cm
12.
Jeroen Homan Rudy Wijnands Albert Kong Jon M. Miller Sabrina Rossi Tomaso Belloni Walter H. G. Lewin 《Monthly notices of the Royal Astronomical Society》2006,366(1):235-237
We report the result of an XMM–Newton observation of the black hole X-ray transient XTE J1650–500 in quiescence. The source was not detected, and we set upper limits on the 0.5–10 keV luminosity of 0.9–1.0 × 1031 erg s−1 (for a newly derived distance of 2.6 kpc). These limits are in line with the quiescent luminosities of black hole X-ray binaries with similar orbital periods (∼7–8 h). 相似文献
13.
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
14.
S. Maret A. Faure E. Scifoni L. Wiesenfeld 《Monthly notices of the Royal Astronomical Society》2009,399(1):425-431
Ammonia inversion lines are often used as probes of the physical conditions in the dense interstellar medium. The excitation temperature between the first two para-metastable (rotational) levels is an excellent probe of the gas kinetic temperature. However, the calibration of this ammonia thermometer depends on the accuracy of the collisional rates with H2 . Here, we present new collisional rates for ortho- and para-NH3 colliding with para-H2 ( J = 0) , and investigate the effects of these new rates on the excitation of ammonia. Scattering calculations employ a new, high-accuracy, potential energy surface computed at the coupled-cluster CCSD(T) level with a basis set extrapolation procedure. Rates are obtained for all transitions involving ammonia levels with J ≤ 3 and for kinetic temperatures in the range 5–100 K. We find that the calibration curve of the ammonia thermometer – which relates the observed excitation temperature between the first two para-metastable levels to the gas kinetic temperature – does not change significantly when these new rates are used. Thus, the calibration of ammonia thermometer appears to be robust. Effects of the new rates on the excitation temperature of inversion and rotation–inversion transitions are also found to be small. 相似文献
15.
Steven R. Furlanetto Michael R. Furlanetto 《Monthly notices of the Royal Astronomical Society》2007,379(1):130-134
The spin temperature of neutral hydrogen, which determines the optical depth and brightness of the 21-cm line, is determined by the competition between radiative and collisional processes. Here, we examine the role of proton–hydrogen collisions in setting the spin temperature. We use recent fully quantum-mechanical calculations of the relevant cross-sections, which allow us to present accurate results over the entire physically relevant temperature range 1–104 K . For kinetic temperatures T K ≳ 100 K , the proton–hydrogen rate coefficient exceeds that for hydrogen–hydrogen collisions by about a factor of 2. However, at low temperatures ( T K ≲ 5 K) H–H+ collisions become several thousand times more efficient than H–H and even more important than H–e− collisions. 相似文献
16.
Nikolai F. Zobov Sergei V. Shirin Roman I. Ovsyannikov Oleg L. Polyansky Robert J. Barber Jonathan Tennyson Peter F. Bernath Michel Carleer Reginald Colin Pierre-François Coheur 《Monthly notices of the Royal Astronomical Society》2008,387(3):1093-1098
The high resolution laboratory spectrum of hot water vapour has been recorded in the 500–13 000 cm−1 wavenumber range and we report on the analysis of the 4750–13 000 cm−1 (0.769–2.1 μm) portion. The emission spectrum was recorded using an oxy-acetylene welding torch and a Fourier transform spectrometer. Line assignments in the laboratory spectrum as well as in an absorption spectrum of a sunspot umbra were made with the help of the BT2 line-list. Our torch spectrum is the first laboratory observation of the 9300 Å'steam bands' seen in M-stars and brown dwarfs. 相似文献
17.
18.
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
19.
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
20.
Michael D. Smith Jochen Eislöffel & Christopher J. Davis 《Monthly notices of the Royal Astronomical Society》1998,297(3):687-691
We demonstrate that a wide range of molecular hydrogen excitation can be observed in protostellar outflows at wavelengths in excess of 5 μm. Cold H2 in DR 21 is detected through the pure rotational transitions in the ground vibrational level (0–0). Hot H2 is detected in pure rotational transitions within higher vibrational levels (1–1, 1–2, etc.). Although this emission is relatively weak, we have detected two 1–1 lines in the DR 21 outflow with the ISO SWS instrument. We thus investigate molecular excitation over energy levels corresponding to the temperature range 1015–15 722 K, without the uncertainty introduced by differential extinction when employing near-infrared data.
This gas is thermally excited. We uncover a rather low H2 excitation in the DR 21 West Peak. The line emission cannot be produced from single C-shocks or J-shocks; a range of shock strengths is required. This suggests that bow shocks and/or bow-generated supersonic turbulence is responsible. We are able to distinguish this shock-excited gas from the fluoresced gas detected in the K band, providing support for the dual-excitation model of Fernandes, Brand & Burton. 相似文献
This gas is thermally excited. We uncover a rather low H