Collisional depolarization and transfer rates of spectral lines by atomic hydrogen

Derouich, M.; Sahal‐Bréchot, S.; Barklem, P. S.

doi:10.1051/0004-6361:20047188

Cited by 21 publications

(63 citation statements)

References 24 publications

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“…A semi-classical theory underlying the calculation of the depolarization and polarization transfer rates by isotropic collisions of ions with neutral hydrogen is detailed and validated in Derouich et al (2004). They found that the percentage of error on the semi-classical rates with respect to the available quantum chemistry rates is 4% to 7% (see Sect.…”

Section: Numerical Resultsmentioning

confidence: 99%

Evidence of collisional depolarization of the Ba II ${\lambda}$4554 line in the low chromosphere

Derouich¹

2008

A&A

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Context. Rigorous modeling of the Ba ii λ4554 formation is potentially interesting since this strongly polarized line forms in the solar chromosphere where the magnetic field is not very well known.Aims. We investigate the role of isotropic collisions with neutral hydrogen in the formation of the polarized Ba ii λ4554 line and, thus, in the determination of the magnetic field.Methods. Multipole relaxation and transfer rates of the d-and p-states of Ba ii by isotropic collisions with neutral hydrogen are calculated. We consider a plane-parallel layer of Ba ii that is situated at the low chromosphere and that is anisotropically illuminated from below, which produces linear polarization in the λ4554 line by scattering processes. To compute that polarization, we solve the statistical equilibrium equations for Ba ii levels including collisions, radiation, and magnetic-field effects.Results. Variation laws of the relaxation and transfer rates with hydrogen number density n H and temperature were deduced. The polarization of the λ4554 line is clearly affected by isotropic collisions with neutral hydrogen, although the collisional depolarization of its upper level 2 P 3/2 is negligible. This is because the alignment of the metastable levels 2 D 3/2 and 2 D 5/2 of the Ba ii are vulnerable to collisions. At the height of formation of the λ4554 line where n H ∼ 2 × 10 14 cm −3 , we find that neglecting the collisions induces ∼25% inaccuracy in the calculation of the polarization and ∼35% inaccuracy on microturbulent magnetic field determination. Conclusions. The polarization of the λ4554 line decreases due to collisions with hydrogen atoms. In addition, during scattering processes collisions could change the frequency of the Ba ii photons. To quantitatively study this line, one should deal with the problem of development of general theory treating partial redistribution of frequencies and including transfer and relaxation rates by collisions for a multilevel atom with hyperfine structure.

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Section: Numerical Resultsmentioning

confidence: 99%

Evidence of collisional depolarization of the Ba II ${\lambda}$4554 line in the low chromosphere

Derouich¹

2008

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“…By comparing to the reference value of C 0 ( 3 2 → 5 2 )(T = 5000K)) given in Equation 17 of Derouich et al (2004), we found that re(Ca II) ≃ 2 %, re(Ba II) ≃ 19 %, re(Sr II) ≃ 4 %. Note that in Derouich et al (2004), the polarization transfer rates are denoted by…”

Section: Polarization Transfer Rates Between the Levelsmentioning

confidence: 68%

“…After that the code of collisions should be run to get the collisional rates level by level. This is a strong restriction which hinders the generalization of the DSB results published in Derouich et al (2004). That restriction has been removed for the p-states of ions in the recent paper of Derouich (2017).…”

Section: Statement Of the Problemmentioning

confidence: 99%

“…The Hanle depolarization allows diagnostics of the magnetic fields by confronting the discrepancy between the polarization modeled in the absence of magnetic fields and the observed polarization (e. g. Stenflo 1982;Landi Degl'Innocenti 1983;Sahal-Bréchot et al 1986;Stenflo 2004;Trujillo Bueno et al 2004;Derouich et al 2006;Faurobert et al 2009). neutral hydrogen (see for example Derouich et al 2003a andDerouich 2004).…”

Section: Introductionmentioning

confidence: 99%

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Scattering Polarisation of the d-States of Ions and Solar Magnetic Field: Effects of Isotropic Collisions

Derouich

Basurah

Badruddin

2017

Publ. Astron. Soc. Aust.

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Analysis of solar magnetic fields using observations as well as theoretical interpretations of the scattering polarization is commonly designated as a high priority area of the solar research. The interpretation of the observed polarization raises a serious theoretical challenge to the researchers involved in this field. In fact, realistic interpretations need detailed investigations of the depolarizing role of isotropic collisions with neutral hydrogen.The goal of this paper is to determine new relationships which allow the calculation of any collisional rates of the d-levels of ions by simply determining the value of n * and Ep without the need of determining the interaction potentials and treating the dynamics of collisions. The determination of n * and Ep is easy and based on atomic data usually available online. Accurate collisional rates allow a reliable diagnostics of solar magnetic fields.In this work we applied our collisional FORTRAN code to a large number of cases involving complex and simple ions. After that, the results are utilized and injected in a genetic programming code developed with C-langugae in order to infer original relationships which will be of great help to solar applications. We discussed the accurarcy of our collisional rates in the cases of polarized complex atoms and atoms with hyperfine structure. The relationships are expressed on the tensorial basis and we explain how to include their contributions in the master equation giving the variation of the density matrix elements.As a test, we compared the results obtained through the general relationships provided in this work with the results obtained directly by running our code of collisions. These comparisons show a percentage of error of about 10% in the average value. Our results could be implemented easily in numerical codes concerned with the simulations of the scattering polarization to obtain accurately the magnetic field in the quiet Sun.

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“…Rough estimates for the depolarizing rates can be obtained from a dipole-dipole van der Waals approximation for the atom-H • (Lamb & ter Haar 1971, see also Landi Degl'Innocenti & Landolfi 2004. More recently, Derouich et al (2003aDerouich et al ( , 2003bDerouich et al ( , 2004aDerouich et al ( , 2004bDerouich et al ( , 2005; Derouich & Barklem (2007) used ab initio interaction potentials and a semi-classical approach using straight line trajectories at different impact parameters. Kerkeni et al (2000); Kerkeni (2002); Kerkeni & Bommier (2002); Kerkeni et al (2003) have calculated depolarizing rates with neutral hydrogen with a fully quantum mechanical approach for the Hamiltonian interaction and dynamics.…”

Section: Introductionmentioning

confidence: 99%

Depolarizing Collisions With Hydrogen: Neutral and Singly Ionized Alkaline Earths

Sainz

Roncero

Sanz-Sanz

et al. 2014

ApJ

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Depolarizing collisions are elastic or quasielastic collisions that equalize the populations and destroy the coherence between the magnetic sublevels of atomic levels. In astrophysical plasmas, the main depolarizing collider is neutral hydrogen. We consider depolarizing rates on the lowest levels of neutral and singly ionized alkali earths Mg i, Sr i, Ba i, Mg ii, Ca ii, and Ba ii, due to collisions with H • . We compute ab initio potential curves of the atom-H • system and solve the quantum mechanical dynamics. From the scattering amplitudes, we calculate the depolarizing rates for Maxwellian distributions of colliders at temperatures T 10,000 K. A comparative analysis of our results and previous calculations in the literature is completed. We discuss the effect of these rates on the formation of scattering polarization patterns of resonant lines of alkali earths in the solar atmosphere, and their effect on Hanle effect diagnostics of solar magnetic fields.

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Collisional depolarization and transfer rates of spectral lines by atomic hydrogen

Cited by 21 publications

References 24 publications

Evidence of collisional depolarization of the Ba II ${\lambda}$4554 line in the low chromosphere

Evidence of collisional depolarization of the Ba II ${\lambda}$4554 line in the low chromosphere

Scattering Polarisation of the d-States of Ions and Solar Magnetic Field: Effects of Isotropic Collisions

Depolarizing Collisions With Hydrogen: Neutral and Singly Ionized Alkaline Earths

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