Depolarisation rates of Ca II s, p and d levels by isotropic collisions with hydrogen atoms

Free access article

Issue		A&A Volume 402, Number 1, April IV 2003


Page(s)		5 - 11
Section		Cosmology
DOI		http://dx.doi.org/10.1051/0004-6361:20030228

A&A 402, 5-11 (2003)
DOI: 10.1051/0004-6361:20030228

Depolarisation rates of Ca II s, p and d levels by isotropic collisions with hydrogen atoms

B. Kerkeni, A. Spielfiedel and N. Feautrier

Laboratoire d'Étude du Rayonnement et de la Matière en Astrophysique, CNRS FRE 2460 - LERMA, Observatoire de Paris, Section de Meudon, 92195 Meudon, France
(Received 30 July 2002 / Accepted 21 January 2003)

Abstract
Multipole relaxation and transfer rates of the ${\rm 4s}^2$ S, $3{\rm d}^2$ D and $4{\rm p}^2$ P states of Ca II due to isotropic collisions with neutral hydrogen atoms are calculated. Evaluation of these rates have been carried out using accurate ab initio potential energy curves. The collisional T-matrix elements required for these calculations have been evaluated in a quantum mechanical description including fine structure splitting. Analytical expressions of all the rates valid for $200~{\rm K}\le T\le 10\,000$ K are given.

Key words: Sun: atmosphere -- atomic processes -- line: formation -- polarization

Offprint request: B. Kerkeni, boutheina.kerkeni@chem.ox.ac.uk

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