S. Sahal−Bréchot

Laboratoire d’Etudes du Rayonnement et de la Matière en Astrophysique et Atmosphères

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M. S. Dimitrijević

Astronomical Observatory

267

V. Bommier

Laboratoire d’études spatiales et d’instrumentation en astrophysique

N. Ben Nessib

King Saud University

Haykel Elabidi

Umm al-Qura University

Zoran Simić

Astronomical Observatory

Magdalena D. Christova

Technical University of Sofia

E. Landi Degl’Innocenti

University of Florence

Rafik Hamdi

University of Carthage

J. L. Leroy

Institut de Chimie des Substances Naturelles

M. Derouich

King Abdulaziz University

Cooperative Institutions

Centre National de la Recherche Scientifique

113

Observatoire de Paris

Sorbonne Université

Université Paris Sciences et Lettres

Université Paris Cité

Janssen (France)

Astronomical Observatory

Laboratoire d’Etudes du Rayonnement et de la Matière en Astrophysique et Atmosphères

Galaxies, Etoiles, Physique et Instrumentation

University of Belgrade

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Contribution to the Semi-Classical and Modified Semi-Empirical Impact Stark Broadening Calculations of Singly Ionized Carbon and Oxygen Spectral Lines.

MSAIS (2005)

Walid Foued Mahmoudi N. Ben Nessib M. S. Dimitrijević S. Sahal−Bréchot

Abstract. Using the semi-classical impact perturbation theory including both dipole andquadrupole terms in the expression of electrostatic interaction between the optical electronand the perturber, we calculated widths and shifts of singly ionized carbon and oxygenspectral lines and compared with experimental results and those calculated by Griem. Theimpact approximation was checked for each case using the appropriate condition of va-lidity (the collision volume must be very small compared to the inverse of the perturberdensity). The species of ionic perturbers depends on the plasma composition in a partic-ular experiment. We also calculated modiﬁed semi-empirical widths using the formalismof Dimitrijevi´c and Konjevi ´c, in order to test the applied method and the accuracy of theobtained results. Key words. line: proﬁles - Atomic data 1. Introduction The charged carbon (CII) and oxygen (OII)atoms, as emitters or absorbers, are especiallyimportant due to their presence in many kindsof cosmic sources of radiation. The abundanceof the large number of ionized carbon and oxy-gen spectral lines in stellar plasmas make theseof great importance for diagnostic purposes.In astrophysics, Stark broadening data are re-quired e.g. for the evaluation of the physical

Carbon fibers

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The Theoretical Impact Polarization of the O I 6300 Å Red Line of Earth Auroræ

V. Bommier S. Sahal−Bréchot J. Dubau M. Cornille

We present a semi-classical theory of the impact polarization due to a quadrupolar electric excitation, well-suited to this forbidden line. In addition, this line is also radiatively forbidden being a triplet-singlet transition. This is overcome by scaling the semi-classical result to a full quantum calculation at a single energy value. The cross-section and impact polarization are thus obtained as a function of energy (with good agreement with the quantum calculated cross-section), and the behavior of the impact polarization is found quite different of the usual one of the dipolar electric interaction. Denoting as radial the polarization parallel to the incident beam or magnetic field, and as tangential the perpendicular polarization, the dipolar interaction (permitted lines) leads to radial polarization at low energy, and tangential polarization at high energy, the polarization vanishing at energy about twelve times the threshold energy. In the case of the quadrupolar electric interaction, we get a quite different behavior, the vanishing point being much closer to the threshold energy. This leads to reanalyze the aurorae red line polarization observation by Lilensten et al. (2008), and to conclude that the line is only weakly radially polarized and only during the auroral events. The weak polarization level leads to consider the competing depolarization by collisions with the neighboring O atoms, whose density could then be diagnosed with further measurements and calculations.

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Influence of Stark broadening within Be III spectral series

Publications de l'Observatoire Astronomique de Beograd (2003)

M. S. Dimitrijević M. Dačić Z. Cvetković S. Sahal−Bréchot

Using a semiclassical perturbation method, we have calculated electron−, proton−, and ionized helium −impact line widths and shifts for 52 Be III multiplets as a function of temperature and perturber density. The obtained results have been used for discussion of regularities and systematic trends along spectral series.

Hydrogen spectral series

Semiclassical physics

Line (geometry)

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Polarisation de la raie H-alpha des Éruptions Solaires

HAL (Le Centre pour la Communication Scientifique Directe) (1993)

V. Bommier G. Chambe N. Feautrier J. C. Hénoux S. Sahal–Bréchot

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Scientific interest for polarimetry in space

HAL (Le Centre pour la Communication Scientifique Directe) (2006)

V. Bommier S. Sahal–Bréchot

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

Astronomy and Astrophysics (2005)

V. Bommier M. Derouich E. Landi Degl’Innocenti G. Molodij S. Sahal–Bréchot

This paper presents and interprets some observations of the limb polarization of 4607 Å obtained with the spectropolarimeter 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 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 interpretation 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 [CITE]), 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 microturbulent 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. ([CITE], Nature, 430, 326), using a 3D magneto-convective simulation. This validates our method.

Hanle effect

Polarimeter

Field strength

10.1051/0004-6361:20035773

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Citations (36)

Stark broadening calculations of neutral copper spectral lines and temperature dependence

Physica Scripta (2010)

Besma Zmerli N. Ben Nessib M. S. Dimitrijević S. Sahal−Bréchot

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.

Homogeneous broadening

Energetic neutral atom

10.1088/0031-8949/82/05/055301

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Citations (48)

Polarization of the hydrogen H alpha _ line in solar flares: contribution of the different radiative and collisional processes.

Astronomy and Astrophysics (1997)

E. Vogt S. Sahal–Bréchot J. C. Hénoux

Solar flare

H-alpha

Hydrogen line

Solar atmosphere

Flare

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Citations (9)

Stark broadening of Al I spectral lines

Physica Scripta (1994)

M. S. Dimitrijević S. Sahal−Bréchot

Using a semiclassical approach, we have calculated electron-, proton- and ionized helium-impact line widths and shifts for 22 Al I multiplets. The resulting data have been compared with existing experimental and theoretical values.

Semiclassical physics

Line (geometry)

10.1088/0031-8949/49/1/005

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Citations (31)

Stark broadened line profiles of neutral strontium lines in plasma conditions

Symposium - International Astronomical Union (1997)

M. S. Dimitrijević S. Sahal−Bréchot

During more than twenty years, we are making a continuous effort to provide Stark-broadening parameters needed for research of astrophysical, laboratory and laser produced plasma. A review of our results is presented in Dimitrijević, 1996). Such data are of interest for the consideration of a number of problems in astrophysics, physics and technology as e.g. for stellar plasma diagnostic, opacity calculations, the investigation/modelling of stellar spectra or a particular line, laboratory plasma diagnostic, laser produced plasmas, thermonuclear research, plasma technology, as well as for different examinations of regularities and systematic trends for e.g. homologous atoms (Dimitrijević and Popović, 1989) or in general (Purić et al. 1991).

Thermonuclear Fusion

Opacity

Line (geometry)

10.1017/s0074180900130402

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Citations (1)