C. J. Zeippen

Atomic data for opacity calculations. XXIII. The aluminium isoelectronic sequence

As a contribution to the international Opacity Project, large numbers of term energies, oscillator strengths and photoionization cross sections have been computed for Al-like ions of astrophysical interest (Al I, Si II, S IV, Ar VI, Ca VIII and Fe XIV), using an ab initio close-coupling approach in LS-coupling. Careful comparisons with previous theoretical and experimental work show that our collisional approach allows a systematic and accurate description of plunging configurations, series perturbations and cancellations typical of these three-valence-electron systems. Even for highly ionized systems such as Fe XIV, the neglect of relativistic effects introduces limited inaccuracies ( approximately 5%) in the average term energies, and the gross features of the distribution of oscillator strengths are accurately delineated. The main contribution of the present study lies in the volume of accurate new data made available to the public through the TOPbase atomic database: 1935 computed multiplets compared to 225 observed ones, 56242 oscillator strengths and photoionization cross sections from 1296 initial states.

Atomic data from the IRON project. LVIII. Electron impact excitation of Fe XII

A new calculation of rate coefficients for electron collisional excitation of Fe XII is presented and compared to earlier calculations. Significant differences are found with all earlier work due to the inclusion of resonance processes that have not previously been considered and to the use of the intermediate coupling frame transformation method. The resulting dataset of collision strengths is shown to resolve many of the outstanding discrepancies between theory and solar observations. In particular, density sensitive line ratios in Fe XII now indicate electron densities close to those derived from other ions of comparable ionization potential.

Atomic data from the IRON Project LI. Electron impact excitation of Fe IX

We calculate collision strengths and thermally averaged collision strengths for electron excitation between the one hundred and forty energetically lowest levels of Fe 8+ . 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.

OPserver: interactive online computations of opacities and radiative accelerations

Codes to compute mean opacities and radiative accelerations for arbitrary chemical mixtures using the Opacity Project recently revised data have been restructured in a client‐server architecture and transcribed as a subroutine library. This implementation increases efficiency in stellar modelling where element stratification due to diffusion processes is depth dependent, and thus requires repeated fast opacity re-estimates. Three user modes are provided to fit different computing environments, namely, a web browser, a local workstation and a distributed grid.

Rovibrational excitation of molecules by He atoms

We present the results of quantum mechanical calculations of cross sections and hence rate coefficients for rovibrational transitions in ortho- and para-, induced by collisions with He. Rovibrational levels up to were included in the calculations, and rate coefficients are available for temperatures . Comparison is made with previous calculations of rate coefficients for pure rotational transitions within the vibrational ground state and with measurements of the rate coefficient for vibrational relaxation at both high and low temperatures. Agreement is found to be good.

Atomic data from the Iron Project - XLIII. Transition probabilities for Fe V

An extensive set of dipole-allowed, intercom- bination, and forbidden transition probabilities for Fe V is presented. The Breit-Pauli R-matrix (BPRM) method is used to calculate 1:46 10 6 oscillator strengths for the allowed and intercombination E1 transitions among 3865 ne-structure levels dominated by conguration complexes with n 10 and l 9. These data are comple- mented by an atomic structure conguration interaction (CI) calculation using the SUPERSTRUCTURE program for 362 relativistic quadrupole (E2) and magnetic dipole (M1) transitions among 65 low-lying levels dominated by the 3d 4 and 3d 3 4s congurations. Procedures have been developed for the identication of the large number of ne-structure levels and transitions obtained through the BPRM calculations. The target ion Fe VI is represented by an eigenfunction expansion of 19 ne-structure levels of 3d 3 and a set of correlation congurations. Fe V bound levels are obtained with angular and spin symmetries SL and J of the (e + Fe VI) system such that 2S +1 =5 , 3, 1,L 10, J 8 of even and odd parities. The completeness of the calculated dataset is veried in terms of all possible bound levels belonging to relevant LS terms and transitions in correspondence with the LS terms. The ne-structure averaged relativistic values are compared with previous Opacity Project LS coupling data and other works. The 362 forbidden transition probabilities considerably extend the available data for the E2 and M1 transtions, and are in good agreement with those computed by Garstang for the 3d 4 transitions.

Radiative opacities for stellar envelopes

Recent advances in the field of opacity calculations for stellar envelopes are summarized. The methods used and the results obtained in the last decade by two independent groups are discussed briefly. Some of the important effects of the new data on astrophysical studies are outlined. Because this review is meant for the 26th EGAS Conference, the size and accuracy of the new set of radiative atomic data produced by the international Opacity Project are emphasized. Potential users of such data are encouraged to get acquainted with the database service known as TOPbase and recently installed at the CDS (Strasbourg, France) for general Internet access.

Level populations for Fe III applicable to astrophysical plasmas and a comparison with planetary nebula observations

Recent R-matrix calculations of electron impact excitation rates in Fe III, which are significantly different from the earlier results of Garstang, Robb, & Rountree, are used to derive relative populations for the 17 fine-structure levels in the 5 D, 3 P, 3 H, 3 F, and 3 G states of the 3d 6 configuration. Populations are presented for a wide range of electron temperatures (T e =5000-20,000 K) and densities (N e =10 2 -10 9 cm −3 ) applicable to astrophysical plasmas

Calculated transition probabilities in highly charged Ti-like ions

A prominent spectral line in the optical range arises in Ti-like ions observed in electron beam ion traps (EBIT) around the world. This line has been heralded as an important diagnostic tool for hot fusion test plasmas. Using a Hartree-Fock approach including relativistic corrections and semi-empirical adjustments, wavelengths and transition probabilities have been calculated for M1 and E2 transitions involving the low-lying levels within the 3d4 configuration of titanium-like ions. The calculated value for the lifetime of the 5D3 level in Xe32+ is in agreement with a recent measurement in an EBIT.

Probabilities for forbidden transitions in atoms and ions: 1989-1995. A commented bibliography

A list is given of references concerning calculated and measured probabilities for forbidden transitions in atoms and ions. The selection is restricted to electric quadrupole (E2), magnetic dipole (M1), magnetic quadrupole (M2) and magnetic octupole (M3) transitions. In particular, spin-forbidden, hyperfine-structure induced and multiphoton transitions are not considered here. Some comments are included on important aspects of recent work in the field. The period covered goes from 1989 to mid-1995. This paper is thus a complement to our previous bibliography on the subject for the period 1968-1989 [Bi?mont, E. and Zeippen, C. J., J. de Physique IV, C1, 209 (1991)].