On the importance of satellite lines to the He-like K ALPHA complex and the G ratio for calcium, iron, and nickel

New, more detailed calculations of the emission spectra of the He-like K ALPHA 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 (n>=3) satellite lines, that K ALPHA 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 are taken into account as independent processes.Comment: 12 pages, 5 figures, to appear in Monthly Notices of the Royal Astronomical Society. The definitive version is available at www.blackwell-synergy.co

The 6.7 keV KALPHA complex of He-like iron in transient plasmas

Time dependent numerical simulations of the K ALPHA complex of Fe XXV are carried out as a function of temperature/density/radiation field variations in high-temperature astrophysical and laboratory plasmas. In addition to several well known features, the transient and steady state spectra reveal the effects due to (a) time-dependent thermal and non-thermal radiation fields, (b) photo and collisional excitation and ionization, and (c) high densities, on the `quartet' of principal w,x,y,z lines, and dielectronic satellites. The highly detailed models show precisely how, assuming a temporal-temperature correlation, the X-ray intensity varies between 6.6 - 6.7 keV and undergoes a `spectral inversion' in the w and z line intensities, characterizing an ionization or a recombination dominated plasma. The dielectronic satellite intensities are the most temperature dependent features, but insensitive to density variations, and significantly contribute to the K ALPHA complex for T < 6.7 keV leading to asymmetric profiles. The 6.7 keV K ALPHA complex should be a potential diagnostic of X-ray flares in AGN, afterglows in gamma-ray bursts, and other non-equilibrium sources with the high-resolution measurements possible from the upcoming mission Astro-E2. It is also shown that high electron densities attenuate the line intensities in simulations relevant to laboratory plasmas, such as in inertial confinement fusion, laser, or magnetic Z-pinch devices.Comment: 13 pages, 4 figures, 1 postscript coversheet. This is a preprint of an article accepted for publication in the Monthly Notices of the Royal Astronomical Societ

Recombination Rate Coefficients for KLL Di-electronic Satellite Lines of Fe XXV and Ni XXVII

The unified method for total electron-ion recombination is extended to study the dielectronic satellite (DES) lines. These lines, formed from radiative decay of autoionizing states, are highly sensitive temperature diagnostics of astrophysical and laboratory plasma sources. The computation of the unified recombination rates is based on the relativistic Breit-Pauli R-matrix method and close coupling approximation. Extending the theoretical formulation developed earlier we present recombination rate coefficients for the 22 satellite lines of KLL complexes of helium-like Fe XXV and Ni XXVII. The isolated resonance approximation, commonly used throughout plasma modeling, treats these resonances essentially as bound features except for dielectronic capture into, and autoionization out of, these levels. A line profile or cross section shape is often assumed. On the other hand, by including the coupling between the autoionizing and continuum channels, the unified method gives the intrinsic spectrum of DES lines which includes not only the energies and strengths, but also the natural line or cross section shapes. A formulation is presented to derive autoionization rates from unified resonance strengths and enable correspondence with the isolated resonance approximation. While the rates compare very well with existing rates for the strong lines to <20%, the differences for weaker DES lines are larger. We also illustrate the application of the present results to the analysis of K ALPHA complexes observed in high-temperature X-ray emission spectra of Fe XXV and Ni XXVII. There are considerable differences with previous results in the total KLL intensity for Fe XXV at temperatures below the temperature of maximum abundance in coronal equilibrium. (Abbreviated Abstract)Comment: 21 pages, 5 figures, to appear in Physica Script

High-temperature behaviour of the helium-like Kα G ratio: the effect of improved recombination rate coefficients for calcium, iron and nickel

Relevant data is available at: http://www.astronomy.ohio-state.edu/~nahar/nahar_radiativeatomicdata/index.htmlThe definitive version is available at www.blackwell-synergy.com. http://www3.interscience.wiley.com/journal/117975880/abstractIt is shown that above the temperature of maximum abundance, recombination rates into the excited states of He-like ions that are calculated using earlier, more approximate methods differ markedly from rates obtained from recent distorted-wave and R-matrix calculations (unified recombination rate coefficients) for Ca, Fe and Ni. The present rates lead to G ratios that are greatly lower than those resulting from the more approximate rates in previous works, by up to a factor of 6 at high electron temperatures. Excellent agreement between the distorted-wave and the R-matrix rates, as well as excellent agreement in the G ratios calculated from them, provides support for the accuracy of these new values which have a broad applicability to the modelling and interpreting of X-ray spectra from a variety of astrophysical and laboratory sources.The work by the OSU group (MM, SNN, AKP) was partially supported by a grant from the NASA Astrophysical Theory Program

X-ray absorption via K-alpha resonance complexes in oxygen ions

The K-alpha resonance complexes in oxygen ions O I - O VI are theoretically computed and resonance oscillator strengths and wavelengths are presented. The highly resolved photoionization cross sections, with relativistic fine structure, are computed in the coupled channel approximation using the Breit-Pauli R-matrix method. A number of strong K-alpha resonances are found to be appreciable, with resonance oscillator strengths f_r > 0.1. The K-alpha resonance wavelengths of O I-O VI lie in a relatively narrow wavelength range 22 - 23.5 A, and the X-ray opacity in this region should therefore be significantly affected by K --> L transitions in oxygen. The results should be useful in the interpretation of soft X-ray spectra observed from Chandra and XMM-Newton.Comment: Monthly Notices of Roy. Astro. Soc. (in press), 10 pgs. 1 figur

A study of the breakdown of the quasi-static approximation at high densities and its effect on the helium-like K ALPHA complex of nickel, iron, and calcium

The General Spectral Modeling (GSM) code employs the quasi-static approximation, a standard, low-density methodology that assumes the ionization balance is separable from a determination of the excited-state populations that give rise to the spectra. GSM also allows for some states to be treated only as contributions to effective rates. While these two approximations are known to be valid at low densities, this work investigates using such methods to model high-density, non-LTE emission spectra and determines at what point the approximations break down by comparing to spectra produced by the LANL code ATOMIC which makes no such approximations. As both approximations are used by other astrophysical and low-density modeling codes, the results should be of broad interest. He-like K$\alpha$ emission spectra are presented for Ni, Fe, and Ca, in order to gauge the effect of both approximations employed in GSM. This work confirms that at and above the temperature of maximum abundance of the He-like ionization stage, the range of validity for both approximations is sufficient for modeling the low- and moderate-density regimes one typically finds in astrophysical and magnetically confined fusion plasmas. However, a breakdown does occur for high densities; we obtain quantitative limits that are significantly higher than previous works. This work demonstrates that, while the range of validity for both approximations is sufficient to predict the density-dependent quenching of the z line, the approximations break down at higher densities. Thus these approximations should be used with greater care when modeling high-density plasmas such as those found in inertial confinement fusion and electromagnetic pinch devices.Comment: Accepted by Physical Review A (http://pra.aps.org/). 11 pages + LANL cover, 5 figures. Will update citation information as it becomes available. Abbreviated abstract is listed her

On the importance of satellite lines to the helium-like Kα complex and the G ratio for calcium, iron and nickel

ABSTRACT 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 &gt; 1 at temperatures well above the temperature of maximum abundance. These new calculations demonstrate, with an improved treatment of the KLn (n ≥ 3) 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