Collision rates for excitation of helium-like ions with inclusion of resonance effects

Abstract. We present He-like line ratios (resonance, intercombination and forbidden lines) for totally and partially photoionized media. For solar plasmas, these line ratios are already widely used for density and temperature diagnostics of coronal (collisional) plasmas. In the case of totally and partially photoionized plasmas, He-like line ratios allow for the determination of the ionization processes involved in the plasma (photoionization with or without an additional collisional ionization process), as well as the density and the electronic temperature.With the new generation of X-ray satellites, Chandra/AXAF, XMM and Astro-E, it will be feasible to obtain both high spectral resolution and high sensitivity observations. Thus in the coming years, the ratios of these three components will be measurable for a large number of non-solar objects.In particular, these ratios could be applied to the Warm Absorber-Emitter, commonly present in Active Galactic Nuclei (AGN). A better understanding of the Warm Absorber connection to other regions (Broad Line Region, Narrow Line Region) in AGN (Seyferts type-1 and type-2, low-and high-redshift quasars...) will be an important key to obtaining strong constraints on unified schemes.We have calculated He-like line ratios, for Z = 6, 7, 8, 10, 12 and 14, taking into account the upper level radiative cascades which we have computed for radiative and dielectronic recombinations and collisional excitation. The atomic data are tabulated over a wide range of temperatures in order to be used for interpreting a large variety of astrophysical plasmas.

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“…inside the n = 2 shell) are very important for density diagnostic purpose. The data are from Zhang & Sampson (1987).…”

Section: Electron Excitation Rate Coefficientsmentioning

confidence: 99%

“…For 1s 2 −1s2l transitions, we have used the effective collision strength values from Zhang & Sampson (1987). These values include both non-resonant and resonant contributions.…”

Section: Electron Excitation Rate Coefficientsmentioning

confidence: 99%

X-ray photoionized plasma diagnostics with helium-like ions. Application to warm absorber-emitter in active galactic nuclei

Porquet

Dubau

2000

Astron. Astrophys. Suppl. Ser.

314

435

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“…Excitation collisional data are also taken from Paper I, which are based on the calculations from Zhang & Sampson (1987) plus the contribution of the upper-level (n > 2) radiative cascades calculated in Paper I (see Paper I for more details).…”

Section: Atomic Data and Improvementsmentioning

confidence: 99%

Line ratios for helium-like ions: Applications to collision-dominated plasmas

Porquet

Mewe

Dubau

et al. 2001

A&A

237

327

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Abstract. The line ratios R and G of the three main lines of He-like ions (triplet: resonance, intercombination, forbidden lines) are calculated for C v, N vi, O vii, Ne ix, Mg xi, and Si xiii. These ratios can be used to derive electron density ne and temperature Te of hot late-type stellar coronae and O, B stars from high-resolution spectra obtained with Chandra (LETGS, HETGS) and XMM-Newton (RGS). All excitation and radiative processes between the levels and the effect of upper-level cascades from collisional electronic excitation and from dielectronic and radiative recombination have been considered. When possible the best experimental values for radiative transition probabilities are used. For the higher-Z ions (i.e. Ne ix, Mg xi, Si xiii) possible contributions from blended dielectronic satellite lines to each line of the triplets were included in the calculations of the line ratios R and G for four specific spectral resolutions: RGS, LETGS, HETGS-MEG, HETGS-HEG. The influence of an external stellar radiation field on the coupling of the 2 3 S (upper level of the forbidden line) and 2 3 P levels (upper levels of the intercombination lines) is taken into account. This process is mainly important for the lower-Z ions (i.e. C v, N vi, O vii) at moderate radiation temperature (T rad ). These improved calculations were done for plasmas in collisional ionization equilibrium, but will be later extended to photo-ionized plasmas and to transient ionization plasmas. The values for R and G are given in extensive tables, for a large range of parameters, which could be used directly to compare to the observations.

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“…The ionization rates are obtained from the work of Dere (2007), while the radiative and dielectronic recombination rates for the ions studied here are obtained from the works of Colgan et al (2004), Badnell (2006a,b), and Bautista & Badnell (2007). The excitation rates are calculated using the method of Dzifčáková & Mason (2008) with the atomic data of Wiese et al (1966), Lin et al (1977), Armour et al (1979), Vainshtein & Safronova (1978, 1980, Martin & Zalubas (1983), Sampson et al (1983), Drake (1986), Zhang & Sampson (1987), Zhang et al (1990), Aggarwal & Kingston (1992), Chen et al (1993), Martin et al (1993Martin et al ( , 1995, and Phillips et al (2005), implemented in the CHIANTI database. We do not use the newest available excitation rates or A values for Si xiii and Si xiv (Aggarwal & Keenan 2010), since these contain calculations only for log(T/K) ≤ 7, which is less than the log(τ/K) inferred from RESIK observations.…”

Section: Methodsmentioning

confidence: 99%

Dielectronic satellite lines and double layers in solar flares

Dzifčáková

Karlický

Dudík

2013

A&A

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Context. Particle acceleration during solar flares results in departures of the distribution of particle energies from the Maxwellian distribution. Apart from the high-energy tail, the bulk of the distribution was recently also found to be significantly affected, due, e.g., to the presence of double layers. Aims. We investigate the influence of several proposed non-Maxwellian distribution functions on the X-ray flare line spectra. The distribution functions considered are sharply peaked and include the n-distribution, the moving Maxwellian distribution, and the distribution formed in strong double layers in the flaring plasma.Methods. Synthetic Si xiid-Si xiv spectra involving allowed and dielectronic transitions at 5−6 Å are calculated numerically. The parameters chosen for the calculations correspond to the impulsive phase of solar flares, as inferred by previous authors.Results. The Si xiid λ5.56/Si xiii λ5.68 and Si xiid λ5.82/Si xiii λ5.68 ratios depend on the relative number of electrons at energies corresponding to the formation of the Si xiid lines. Therefore, these ratios increase with the increasing narrowness of the peak of the electron distribution function. The highest ratios are achieved for the distribution formed in double layers, while the moving Maxwellian distribution is less likely to reproduce the observed enhancement of Si xiid intensities. However, the ratio of the allowed Si xiv λ5.22/Si xiii λ5.68 transitions depends on the ionization equilibrium. This ratio is very small for the double-layer distribution.Combination of the double-layer distribution with a Maxwellian distribution with the same mean energy significantly enhances this ratio, while keeping the Si xiid intensities sufficiently increased to explain the characteristics of the observed spectra.Conclusions. These results support the presence of double layers in the plasma during impulsive phase of solar flares.

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Collision rates for excitation of helium-like ions with inclusion of resonance effects

Cited by 91 publications

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X-ray photoionized plasma diagnostics with helium-like ions. Application to warm absorber-emitter in active galactic nuclei

X-ray photoionized plasma diagnostics with helium-like ions. Application to warm absorber-emitter in active galactic nuclei

Line ratios for helium-like ions: Applications to collision-dominated plasmas

Dielectronic satellite lines and double layers in solar flares

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