Sylvie Sahal-Brechot

The magnetic field in the prominences of the polar crown

The Hanle effect method has been applied to the determination of the magnetic field in 120 prominences of the polar crown observed during the 1974–1980 period, which is the ascending phase of cycle XXI. The average field strength which was about 6 G at the beginning of the cycle reached twice this value just before the maximum. There is also a clear trend for a increase of the prominence field with the altitude. We confirm the fact that the magnetic vector makes a small angle (25 °) with the long axis of the prominence. As to the field orientation, we show that the most striking feature lies in the regular pattern of the component which is parallel to the axis of the filament; its direction seems to depend closely on the polarities of the high latitude photospheric field.

Complete determination of the magnetic field vector and of the electron density in 14 prominences from linear polarizaton measurements in the HeI D3 and Hα lines

The present paper is devoted to the interpretation of linear polarization data obtained in 14 quiescent prominences with the Pic-du-Midi coronagraph-polarimeter by J. L. Leroy, in the two lines Hei D3 andHα quasi-simultaneously. The linear polarization of the lines is due to scattering of the anisotropic photospheric radiation, modified by the Hanle effect due to the local magnetic field. The interpretation of the polarization data in the two lines is able to provide the 3 components of the magnetic field vector, and one extra parameter, namely the electron density, because the linear polarization of Hα is also sensitive to the depolarizing effect of collisions with the electrons and protons of the medium. Moreover, by using two lines with different optical thicknesses, namely Hei D3, which is optically thin, and Hα, which is optically thick (τ = 1), it is possible to solve the fundamental ambiguity, each line providing two field vector solutions that are symmetrical in direction with respect to the line of sight in the case of the optically thin line, and which have a different symmetry in the case of the optically thick line.It is then possible to determine without ambiguity the polarity of the prominence magnetic field with respect to that of the photospheric field: 12 prominences are found to be Inverse polarity prominences, whereas 2 prominences are found to be Normal polarity prominences. It must be noticed that in 12 of the 14 cases, the line-of-sight component of the magnetic field vector has a Normal polarity (to the extent that the notion of polarity of a vector component is meaningful; no polarity can be derived in the 2 remaining cases); this may explain the controversy between the results obtained with methods based on the Hanle effect with results obtained through the Zeeman effect. A dip of the magnetic field lines across the prominence has been assumed, to which the optically thick Hα line is sensitive, and the optically thin Hei D3 line is insensitive.For the Inverse prominences, the average field strength is 7.5±1.2 G, the average angle,α, between the field vector and the prominence long axis is 36° ± 15°, the average angle, ζ, between the outgoing field lines and the solar surface at the prominence boundary is 29° ± 20°, and the average electron density is 2.1 × 1010 ± 0.7 × 1010 cm−3. For the Normal prominences, the average field strength is 13.2±2.0 G, the average angle,α, between the field vector and the prominence long axis is 53° ± 15°, the average angle, ζ, between the outgoing field lines and the solar surface at the prominence boundary is 0° ± 20° (horizontal field), and the average electron density is 8.7 × 109 ± 3.0 × 109 cm−3.

Stark profiles of some ion lines of alkaline earth elements

The widths and shifts of Mg+, Ca+, Sr+ and Ba+ lines broadened by electron and ion Stark effects have been measured in an argon welding type plasma. The electron density is about 1.3×1017 cm-3 and the temperature is about 13,000°K. Special care was taken to avoid self-absorption of resonance lines. Injection of alkaline earth elements into the cold region of the plasma edge permitted reliable measurements of the signs of line-shifts. Experimental results are compared with semi-classical theories and a new-classical computation of Sahal-Brechot in which resonances of elastic cross sections are taken into account. Good agreement is observed between experiment and the later calculations.

The Virtual Atomic and Molecular Data Centre (VAMDC) Consortium

The Virtual Atomic and Molecular Data Centre (VAMDC) Consortium is a worldwide consortium which federates atomic and molecular databases through an e-science infrastructure and an organisation to support this activity. About 90% of the inter-connected databases handle data that are used for the interpretation of astronomical spectra and for modelling in many fields of astrophysics. Recently the VAMDC Consortium has connected databases from the radiation damage and the plasma communities, as well as promoting the publication of data from Indian institutes. This paper describes how the VAMDC Consortium is organised for the optimal distribution of atomic and molecular data for scientific research. It is noted that the VAMDC Consortium strongly advocates that authors of research papers using data cite the original experimental and theoretical papers as well as the relevant databases.

Interpretation of second solar spectrum observations of the Sr I 4607 Å line in a quiet region: Turbulent magnetic field strength determination

This paper presents and interprets some observations of the limb polarization of Sr  4607 A obtained with the spec- tropolarimeter of the French-Italian telescope THEMIS in quiet regions close to the solar North Pole on 2002 December 7-9. The linear polarization was measured for a series of limb distances ranging from 4 to 160 arcsec, corresponding to heights of optical depth unity in the line core ranging from about 330 to 220 km, respectively, above the τ5000 = 1 level. To increase the polarimetric sensitivity, the data were averaged along the spectrograph slit (one arcmin long) set parallel to the solar limb. Since the data show no rotation of the linear polarization direction with respect to the limb direction, the observed depolarization is ascribed to the Hanle effect of a turbulent weak magnetic field, the zero-field polarization being derived from a model. The in- terpretation is performed by means of an algorithm which describes the process of line formation in terms of the atomic density matrix formalism, the solar atmosphere being described by an empirical, plane-parallel model. The collisional rates entering the model (inelastic collisions with electrons, elastic depolarizing collisions with neutral hydrogen), have been computed by applying fast semi-classical methods having a typical accuracy of the order of 20% or better (see Derouich 2004), leading to 6% inaccuracy on the magnetic field strength determination. We assume a unimodal distribution for the intensity of the turbulent field. The computed intensity profile has been adjusted to the observed one in both depth and width, by varying both micro- turbulent and macroturbulent velocities. The best adjustment is obtained for respectively 1.87 km s −1 (micro) and 1.78 km s −1 (macro). The evaluation of the magnetic depolarization leads then to the average value of 46 Gauss for the turbulent magnetic field strength, with a gradient of −0.12 Gauss/km. Our results are in very good agreement with the value of 60 Gauss determined at large µ, in the volume-filling field case, by Trujillo Bueno et al. (2004, Nature, 430, 326), using a 3D magneto-convective simulation. This validates our method.

VAMDC--The Virtual Atomic and Molecular Data Centre--A New Way to Disseminate Atomic and Molecular Data--VAMDC Level 1 Release

The Virtual Atomic and Molecular Data Centre (VAMDC, http://www.vamdc.eu/) is a European‐Union‐funded collaboration between groups involved in the generation, evaluation, and use of atomic and molecular data. VAMDC aims to build a reliable, open, flexible and interoperable e‐science interface to existing atomic and molecular data. The project will cover establishing the core consortium, the development and deployment of the infrastructure and the development of interfaces to the existing atomic and molecular databases. This paper describes the organisation of the project and the achievements during its first year.

Stark broadening calculations of neutral copper spectral lines and temperature dependence

The aim of this work is to theoretically determine Stark broadening parameters of 5105.54, 5700.24, 5782.13, 3273.96 and 3247.54 A neutral copper spectral lines. Our results are compared with available experimental and other theoretical data. The results obtained are also used for the continuation of our investigation of the temperature dependence of Stark widths of neutral atom spectral lines in order to improve existing methods for the scaling of Stark broadening parameters with temperature.

The STARK-B database VAMDC node: a repository for spectral line broadening and shifts due to collisions with charged particles

Accurate spectroscopic diagnostics and modeling require the knowledge of numerous collisional line profiles. Access to such data via an online database has become indispensable. The STARK-B database is aimed at meeting these needs for widths and shifts of isolated lines of neutral and ionized elements due to electron and ion impacts. This database of the Paris Observatory is a result of scientific cooperation between S Sahal-Brechot (LERMA) and M S Dimitrijevic (AOB). Access to it is free, and it was opened online at the end of 2008. STARK-B is a node of the Virtual Atomic and Molecular Data Centre (VAMDC) and thus complies with VAMDC and Virtual Observatory standards. VAMDC is a European Union-funded collaboration among groups involved in the generation and use of interoperable atomic and molecular data. STARK-B now contains all our semiclassical-perturbation (SCP) calculated data for more than 123 neutral or ionized elements as published in international refereed journals. It is devoted to modeling and spectroscopic diagnostics of stellar atmospheres and envelopes, laboratory plasmas, laser equipment, and technological plasmas. Hence, the range of temperatures and densities covered by the tables is broad and depends on the ionization degree of the radiating atom. The modified semiempirical (MSE) results of calculations have begun to be implemented. In this paper, we highlight the key points of the method and the assumptions used in the calculations, which have lately been revisited. Then we present the database and its recent developments, as well as our ongoing work and our plans for the future.

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 [term energy corrections (TEC)] for the calculation of the energy levels. These atomic data are used to provide semiclassical electron-, proton- and ionized helium-impact linewidths and shifts for 15 Si vi multiplet. Calculated results have been used to consider the influence of Stark broadening for DO white dwarf atmospheric conditions.

Stark broadening of Cd I spectral lines

Stark broadening parameters, widths, and shifts for 33