Radiative transfer with J-state interference in a two-term atom

Partial frequency redistribution in the non-magnetic case

¹ Indian Institute of Astrophysics, Koramangala, Bangalore, India
e-mail: smithahn@iiap.res.in; knn@iiap.res.in; sampoorna@iiap.res.in
² Institute of Astronomy, ETH Zurich, 8093 Zurich, Switzerland
e-mail: stenflo@astro.phys.ethz.ch
³ Istituto Ricerche Solari Locarno, Via Patocchi, 6605 Locarno-Monti, Switzerland

Received: 23 June 2011
Accepted: 29 August 2011

Abstract

Context. Quantum interference phenomena play a fundamental role in the formation of linear polarization that arises from scattering processes in multiplets of the solar spectrum. In particular, the J-state interference between different line components of a multiplet (arising from transitions in a two-term atom) produces significant effects in the linearly polarized spectra.

Aims. We aim to solve the polarized radiative transfer equation for a two-term atom with the unpolarized lower term in isothermal slabs, including the effect of the interference between the upper J-states and partial frequency redistribution (PRD). We consider only the case of non-magnetic scattering.

Methods. The PRD matrix for the J-state interference derived in previous works is incorporated into the polarized transfer equation. The standard form of the two-level atom transfer equation is extended to a two-term atom. The transfer problem is then solved using a traditional polarized approximate lambda iteration method.

Results. We show how the PRD and the J-state interference together affect the shapes of the (I,Q/I) profiles. We present the benchmark solutions for isothermal, constant-property slabs of a given optical thickness. We consider a hypothetical doublet produced by an L = 0 → 1 → 0 scattering transition with spin S = 1/2. We present the results in the form of Stokes (I,Q/I) profiles for different values of (i) the line separation, (ii) optical thickness, (iii) thermalization parameter, and (iv) the continuum opacity.