Atomic data from the IRON project - LI. Electron impact excitation of FeIX

We calculate collision strengths and thermally averaged collision strengths for electron excitation between the one hundred and forty energetically lowest levels of Fe8+. The scattering target is more elaborate than in any earlier work and large increases are found in the excitation rates among the levels of the 3s(2)3p(5)3d electron configuration due to resonance series that have not been considered previously. The implications for solar and stellar spectroscopy have been discussed elsewhere (Storey & Zeippen 2001). We correct some errors that were made in generating the figures given in that paper and present corrected versions

The influence of electron collisions on non-LTE Li line formation in stellar atmospheres

The influence of the uncertainties in the rate coefficient data for electron-impact excitation and ionization on non-LTE Li line formation in cool stellar atmospheres is investigated. We examine the electron collision data used in previous non-LTE calculations and compare them to recent calculations that use convergent close-coupling (CCC) techniques and to our own calculations using the R-matrix with pseudostates (RMPS) method. We find excellent agreement between rate coefficients from the CCC and RMPS calculations, and reasonable agreement between these data and the semi-empirical data used in non-LTE calculations up to now. The results of non-LTE calculations using the old and new data sets are compared and only small differences found: about 0.01 dex (~ 2%) or less in the abundance corrections. We therefore conclude that the influence on non-LTE calculations of uncertainties in the electron collision data is negligible. Indeed, together with the collision data for the charge exchange process Li(3s) + H Li^+ + H^- now available, and barring the existence of an unknown important collisional process, the collisional data in general is not a source of significant uncertainty in non-LTE Li line formation calculations.Comment: 8 pages, accepted by Astronomy and Astrophysics; Replaced with minor corrections following proof

Photodetachment study of He^- quartet resonances below the He(n=3) thresholds

The photodetachment cross section of He^- has been measured in the photon energy range 2.9 eV to 3.3 eV in order to investigate doubly excited states. Measurements were made channel specific by selectively detecting the residual He atoms left in a particular excited state following detachment. Three Feshbach resonances were found in the He(1s2p ^3P)+e^-(epsilon p) partial cross section: a ^4S resonance below the He(1s3s ^3S) threshold and two ^4P resonances below the He(1s3p ^3P) threshold. The measured energies of these doubly excited states are 2.959260(6) eV, 3.072(7) eV and 3.26487(4) eV. The corresponding widths are found to be 0.20(2) meV, 50(5) meV and 0.61(5) meV. The measured energies agree well with recent theoretical predictions for the 1s3s4s ^4S, 1s3p^2 ^4P and 1s3p4p ^4P states, respectively, but the widths deviate noticeably from calculations for 1s3p^2 ^4P and 1s3p4p ^4P states.Comment: 10 pages, 3 figures, LaTeX2e scrartcl, amsmath. Accepted by Journal of Physics B; minor changes after referee repor

Ionization Structure and Spectra of Iron in Gaseous Nebulae}

The emission spectra and the ionization structure of the low ionization stages of iron, Fe I--IV, in gaseous nebulae are studied. This work includes: (i) new atomic data: photoionization cross sections, total e-ion recombination rates, excitation collision strengths, and transition probabilities; (ii) detailed study of excitation mechanisms for the [Fe II], [Fe III], and [Fe IV] emission, and spectroscopic analysis of the observed IR, optical, and UV spectra; (iii) study of the physical structure and kinematics of the nebulae and their ionization fronts. Spectral analysis of the well observed Orion nebula is carried out as a test case, using extensive collisional-radiative and photoionization models. It is shown that the [Fe II] emission from the Orion nebula is predominantly excited via electron collisions in high density partially ionized zones; radiative fluorescence is relatively less effective. Further evidence for high density zones is derived from the [O I] and [Ni II] spectral lines, as well as from the kinematic measurements of ionic species in the nebula. The ionization structure of iron in Orion is modeled using the newly calculated atomic data, showing some significant differences from previous models. The new model suggests a fully ionized H II region at densities on the order of $10^3$ cm$^{-3}$, and a dynamic partially ionized H II/H I region at densities of $10^5-10^7$ \cm3. Photoionization models also indicate that the optical [O I] and [Fe II] emission originates in high density partially ionized regions within ionization fronts. The gas phase iron abundance in Orion is estimated from observed spectra.Comment: AAS LaTex, 60 pages 18 figures. Astrophysical Journal. in pres

PHOTOIONISATION OF ATOMS AND IONS : AN EXTENDED BIBLIOGRAPHY FOR 1986-1990

Une liste de plus de 900 publications parues en 1986-90 sur les transitions lié-libre induites par impact photonique dans les systèmes atomiques est présentée. Ce travail étend la bibliographie 1970-87 de Butler et al (1988) sur la photoionisation des atomes et des ions dans deux directions. D'une part, elle élargit le domaine d'investigation systématique à l'ionisation simple et multiple, directe et résonnante, impliquant des couches externes ou internes, induite par un seul ou un grand nombre de photons, en présence ou non de champs statiques externes. D'autre part, elle affine l'indexation des références obtenues qui sont classées simultanément par espèce, type de processus et de travail.A list of over 900 references published during the period 1986-90 on bound-free transitions induced by photon-impact in atomic systems is presented. This work extends the 1970-87 bibliography of Butler et al (1988) on the photoionisation of atoms and ions in two directions. On one hand, it enlarges the domain of systematic investigation to simple and multiple ionisation, direct and resonant, implying outer and inner shells, induced by a single or a large number of photons, with or without the presence of external static fields. On the other hand, it refines the indexation of the selected references by species, type of process and of work

Hyperspherical close-coupling calculation of integral cross sections for the reaction H+H2→H2+H

International audienc

Quantum-mechanical calculation of integral cross sections for the reaction F+H2(v=0, j=0)→FH(v′ j′)+H by the hyperspherical method

International audienc

Hyperspherical description of collinear reactive scattering

International audienc