Stark broadening of B IV spectral lines

Stark broadening parameters for 157 multiplets of helium like boron (B IV) have been calculated using the impact semiclassical perturbation formalism. Obtained results have been used to investigate the regularities within spectral series. An example of the influence of Stark broadening on B IV lines in DO white dwarfs is given.Comment: 6 pages, 2 figure

Stark broadening of B IV lines for astrophysical and laboratory plasma research

Stark broadening parameters for 36 multiplets of B IV have been calculated using the semi-classical perturbation formalism. Obtained results have been used to investigate the regularities within spectral series and temperature dependence.Comment: 8 pages, 6 figures, 1 table, in press in Advances in Space Researc

The OIV 1407.3\AA /1401.1\AA\ emission-line ratio in a plasma

Line ratio of O IV 1407.3 \AA/1401.1 \AA\- is calculated using mostly our own atomic and collisional data. Energy levels and oscillator strengths needed for this calculation have been calculated using a Hartree-Fock relativistic (HFR) approach. The electron collision strengths introduced in the statistic equilibrium equations are fitted by polynomials for different energies. Comparison has also been made with available theoretical results. The provided line ratio has been obtained for a set of electron densities from $10^{8}$ cm$^{-3}$ to $10^{13}$ cm$^{-3}$ and for a fixed temperature of 50 000 K.Comment: 6 pages, 1 figure, 2 tables. Accepted for publication in Advances in Space Researc

The STARK-B database as a resource for \textquotedblleft STARK" widths and shifts data: State of advancement and program of development

\textquotedblleft Stark" broadening theories and calculations have been extensively developed for about 50 years and can now be applied to many needs, especially for accurate spectroscopic diagnostics and modeling. This requires the knowledge of numerous collisional line profiles. Nowadays, the access to such data via an online database becomes essential. STARK-B is a collaborative project between the Astronomical Observatory of Belgrade and the Laboratoire d'\'Etude du Rayonnement et de la mati\`ere en Astrophysique (LERMA). It is a database of calculated widths and shifts of isolated lines of atoms and ions due to electron and ion collisions (impacts). It is devoted to modeling and spectroscopic diagnostics of stellar atmospheres and envelopes, laboratory plasmas, laser equipments and technological plasmas. Hence, the domain of temperatures and densities covered by the tables is wide and depends on the ionization degree of the considered ion. STARK-B has been fully opened since September 2008 and is in free access. The first stage of development was ended in autumn 2012, since all the existing data calculated with the impact semiclassical-perturbation method and code by Sahal-Br\'echot, Dimitrijevi\'c and coworkers have now been implemented. We are now beginning the second stage of the development of STARK-B. The state of advancement of the database and our program of development are presented here, together with its context within VAMDC. VAMDC (Virtual Atomic and Molecular Data Center) is an international consortium which has built a secure, documented, flexible interoperable platform e-science permitting an automated exchange of atomic and molecular data.Comment: 4 pages, in press in Advances in Space Researc

Stark Broadening in Compact Stars: Xe VI Lines

International audienceWe will consider Stark broadening of non hydrogenic spectral lines in the impact approximation in compact stars: pre-white dwarf and white dwarf atmospheres. In order to show an example, Stark broadening parameters have been calculated, using the impact semiclassical perturbation approach for four Xe VI spectral lines. Obtained results have been used to demonstrate the influence of Stark broadening in DA and DB white dwarf atmospheres

Collaboration between Paris and Belgrade Observatories in scientific researches on Spectral Line Shapes

International audienc

Case studies on recent Stark broadening calculations and STARK-B database development in the framework of the European project VAMDC (Virtual Atomic and Molecular Data Center)

International audienceStark broadening theories and calculations have been extensively developed for about 50 years. The theory can now be considered as mature for many applications, especially for accurate spectroscopic diagnostics and modelling. In astrophysics, with the increasing sensitivity of observations and spectral resolution, in all domains of wavelengths from far UV to infrared, it has become possible to develop realistic models of interiors and atmospheres of stars and interpret their evolution and the creation of elements through nuclear reactions. For hot stars, especially white dwarfs, Stark broadening is the dominant collisional line broadening process. This requires the knowledge of numerous profiles, especially for trace elements, which are used as useful probes for modern spectroscopic diagnostics. Hence, calculations based on a simple but enough accurate and fast method, are necessary for obtaining numerous results. Ab initio calculations are a growing domain of development. Nowadays, the access to such data via an on line database becomes crucial. This is the object of STARK-B, which is a collaborative project between the Paris Observatory and the Astronomical Observatory of Belgrade. It is a database of calculated widths and shifts of isolated lines of atoms and ions due to electron and ion collisions. It is devoted to modelling and spectroscopic diagnostics of stellar atmospheres and envelopes. In addition, it is relevant to laboratory plasmas, laser equipments and technological plasmas. It is a part of VAMDC (Virtual Atomic and Molecular Data Centre), which is an European Union funded collaboration between groups involved in the generation and use of atomic and molecular data

From collisional line broadening to atomic polarization and collisional depolarization; Astrophysical applications

International audienceAs is well known, interpretation of spectral line shapes is essential for spectroscopic modeling in the laboratory and in astrophysics. Line broadening by collisions offers a tool for spectroscopic diagnostics of scalar physical quantities, especially densities of perturbers. Thanks to the growing accuracy and sensitivity of spectropolarimetric observations and to the progress of MHD modeling, interpretation of all the Stokes parameters of spectral lines nowadays becomes crucial and new tools leading to the determination of vectorial (or anisotropic) physical quantities have been created and are of increasing interest. In particular, interpretation of atomic polarization enables us to determine magnetic field vectors, velocity field vectors, and also to interpret anisotropic excitation of the atomic levels by collimated beams of energetic particles. Atomic polarization leads to a global polarization of the observed line. It is a consequence of a departure from LTE between the Zeeman sublevels, and is due to an anisotropic excitation of the atomic levels. This anisotropic excitation is often the result of the incident radiation field absorption. However, isotropic collisions between Zeeman sublevels try to restore LTE and to destroy this atomic polarization. So, a quantitative interpretation of these spectropolarimetric observations must take into account collisional depolarization (and also the possible polarization transfer between levels). In some cases, collisional depolarization can also be used for determining densities of perturbers. In fact, collisional line broadening, atomic polarization and collisional theories are two complementary theories based on the same key approximations: "no back reaction" and "impact theory". For collisional widths and shifts, the pioneering work by Baranger created in the end of the fifties, was followed by many fruitful developements. For atomic polarization, the theory of the master equation, was created by Fano in the fifties and developed for polarization studies at the end of the sixties and seventies in the pioneering works by Cohen-Tannoudji and coworkers. It has also been extended by many fertile developments, in particular for astrophysics. The main features of the formalism of atomic polarization and colisional depolarization will be presented in parallel with collisional line broadening and astrophysical applications, especially for solar physics, will be reported

Collisional Line Broadening and Collisional Depolarization of Spectral Lines: Similarities and Differences

International audienceThe collisional width of a spectral line takes part in the frequency re- distribution of the scattered radiation in the line. Within the impact approximation, collisional line broadening parameters (widths and shifts), depolarization and polariza- tion transfer rates seem very similar: both include the effect of collisional transitions between the Zeeman sublevels of a given level, or between fine or hyperfine structure levels of a given term. However, there are important differences. On the one hand, for line broadening, the two levels connected by the radiative transition contribute to the broadening. There is also an interference term between the two levels of the line, which can be very important for collisions with neutral hydrogen. On the other hand, only one level or two close levels are concerned in the depolarization. Another difference lies in the fact that elastic cross-sections of the two levels contribute to the line broadening, whereas they do not contribute to the depolarization. The possibility to find some the- oretical relationships concerning depolarization versus collisional broadening will be shown to be impossible. The perturbation expansion of the collisional S matrix and the Van der Waals interaction potential are recalled to be unsuitable, since all the derived parameters are too small (by approximately a factor 2). Finally, in the light of a very recent paper, numerical relationships between line widths and level depolarization rates will be quoted