J-state interference signatures in the second solar spectrum

Modeling the Cr i triplet at 5204–5208 Å

¹ Indian Institute of Astrophysics, Koramangala, Bangalore, India
e-mail: smithahn@iiap.res.in
² Institute of Astronomy, ETH Zurich, 8093 Zurich, Switzerland
³ Istituto Ricerche Solari Locarno, via Patocchi, 6605 Locarno-Monti, Switzerland

Received: 16 November 2011
Accepted: 20 March 2012

Abstract

The scattering polarization in the solar spectrum is traditionally modeled with each spectral line treated separately, but this is generally inadequate for multiplets where J-state interference plays a significant role. Through simultaneous observations of all the 3 lines of a Cr i triplet, combined with realistic radiative transfer modeling of the data, we show that it is necessary to include J-state interference consistently when modeling lines with partially interacting fine structure components. Polarized line formation theory that includes J-state interference effects together with partial frequency redistribution for a two-term atom is used to model the observations. Collisional frequency redistribution is also accounted for. We show that the resonance polarization in the Cr i triplet is strongly affected by the partial frequency redistribution effects in the line core and near wing peaks. The Cr i triplet is quite sensitive to the temperature structure of the photospheric layers. Our complete frequency redistribution calculations in semi-empirical models of the solar atmosphere cannot reproduce the observed near wing polarization or the cross-over of the Stokes Q/I line polarization about the continuum polarization level that is due to the J-state interference. When however partial frequency redistribution is included, a good fit to these features can be achieved. Further, to obtain a good fit to the far wings, a small temperature enhancement of the FALF model in the photospheric layers is necessary.