Atomic data and electron-impact broadening effect in DO white dwarf atmospheres: Si VI

Energy levels, electric dipole transition probabilities and oscillator strengths in five times ionized silicon have been calculated in intermediate coupling. The present calculations were carried out with the general purpose atomic-structure program SUPERSTRUCTURE. The relativistic corrections to the non-relativistic Hamiltonian are taken into account through the Breit-Pauli approximation. We have also introduced a semi-empirical correction (TEC) for the calculation of the energy-levels. These atomic data are used to provide semiclassical electron-, proton- and ionized helium- impact line widths and shifts for 15 Si VI muliplet. Calculated results have been used to consider the influence of Stark broadening for DO white dwarf atmospheric conditions.Comment: MNRAS, accepted, 14 page

Semi-classical collisional functions in a strongly correlated plasma

Collisions between atoms (or ions) and electrons play an important role in the interpretation of line spectra and for the modelling of stellar interiors. Plasma shielding effects due to electron and ion correlations are not negligible in the physical conditions of white dwarf atmospheres, owing to their high density. They also play a role in cool stars and for atomic transitions that are quasi-degenerate. In the standard formalism of Stark impact broadening of spectral lines and of cross sections, the electrostatic Coulomb potential is used to describe the interaction between the perturbing electrons and the emitting atom. Electronic correlations (screening effects) are usually taken into account by introducing a cut-off in the interaction when the electron-atom distance exceeds the Debye radius $R_{{\rm D}}$. A more consistent treatment to describe collective effects is the Debye-Hückel potential: the two-particle Coulomb field is shielded by the ensemble of the surrounding electrons. This is a good approximation only for high temperature and low density plasmas (weakly non-ideal plasmas), while for strongly non-ideal plasmas, the Coulomb cut-off potential or the ion sphere potential are more appropriate. These potentials, which can be written as the Coulomb potential with two correcting terms, are widely used in the literature.
In this paper, we investigate the ion sphere model to describe the electron atom interaction in a strongly coupled plasma. New semi-classical collisional functions are derived for both the transition probability and the cross section, using the classical path approximation

Semi-classical collisional functions in a strongly correlated plasma

An unfortunate error has been found in the expression (Eq. (31)) of the ion sphere potential in Ben Chaouacha et al. (2004, A&A, 419, 771). Corrected expressions are given and the associated collisional functions are replotted

Quantum model of emission in a weakly non ideal plasma

We present, in this work a simple analytical expression of line emission in weakly non ideal plasma using a simplified quantum model. This formalism allows to explain the variations of the line widths with the density in a weakly non ideal plasma. We apply this model to plasma neutral helium lines HeI 6678 Å and HeI 5876 Å and explain the non linearity of the line width

Atomic structure of the carbon like ion Ca XV

International audienc

On the Stark broadening of some Cr II spectral lines in plasma

International audienc

Quantum Stark broadening of 3s–3p spectral lines in Li-like ions; Z-scaling and comparison with semi-classical perturbation theory

Quantum mechanical results for the electron impact Stark widths of the 3s–3p transitions in ten Li-like ions from C IV to P XIII are carried out. The atomic structure is obtained through a scaled Thomas-Fermi-Dirac-Amaldi potential (SST numerical code) with relativistic corrections. The distorted wave method is used for the calculation of the S-Matrix, and Feshbach resonances are included by means of the Gailitis method. A comparison with other theoretical and available experimental results is done. Except for Ne VIII, we find that the agreement between our quantum results and the experiments gets better when Z increases, which is not the case for the available close-coupling quantum ones. The behavior of the Stark width with the charge Z and the electron temperature Te is also studied and in contrast to previous studies, an improved agreement with experimental Z-scaling is obtained. We show that the relative difference between widths of the two fine structure lines of the same multiplet increases with Z from 0.5% for C IV to about 12% for P XIII, proving the increasing importance of fine structure effects. The importance of the Feshbach resonances is discussed and a comparison with available semi-classical perturbation results is given

Modified semiempirical electron width calculations of singly-ionized oxygen spectral lines

Using a modified semiempirical approach, we have calculated Stark broadening full widths at half maximum for 25 OII multiplets for temperatures from 5000 K up to 80 000 K using the needed oscillator strengths from the sophisticated atomic structure data base TOPbase. Then we compared our results with experimental data for 41 OII spectral lines and with the available semi-classical calculations to test the applied method and the accuracy of the results obtained