MODELING THE QUANTUM INTERFERENCE SIGNATURES OF THE Ba II D₂4554 Å LINE IN THE SECOND SOLAR SPECTRUM

Abstract

Quantum interference effects play a vital role in shaping the linear polarization profiles of solar spectral lines. The Ba ii D 2 line at 4554Å is a prominent example, where the F -state interference effects due to the odd isotopes produce polarization profiles, which are very different from those of the even isotopes that have no F -state interference. It is therefore necessary to account for the contributions from the different isotopes to understand the observed linear polarization profiles of this line. Here we do radiative transfer modeling with partial frequency redistribution (PRD) of such observations while accounting for the interference effects and isotope composition. The Ba ii D 2 polarization profile is found to be strongly governed by the PRD mechanism. We show how a full PRD treatment succeeds in reproducing the observations, while complete frequency redistribution (CRD) alone fails to produce polarization profiles that have any resemblance with the observed ones. However, we also find that the line center polarization is sensitive to the temperature structure of the model atmosphere. To obtain a good fit to the line center peak of the observed Stokes Q/I profile, a small modification of the FALX model atmosphere is needed, by lowering the temperature in the line-forming layers. Because of the pronounced temperature sensitivity of the Ba ii D 2 line it may not be a suitable tool for Hanle magnetic-field diagnostics of the solar chromosphere, because there is currently no straightforward way to separate the temperature and magnetic-field effects from each other.

The Quantum Interference Effects in the Sc Ii 4247 Å Line of the Second Solar Spectrum

“…Here we extend our previous work on the Ba ii D 2 line (Smitha et al 2013) to study the Sc ii line at 4247 Å. This line arises due to the transition J = 2 → J = 2.…”

“…The Voigt profile function: For the case of Sc ii 4247 Å line, the Voigt profile function defined in Equation (3) of Smitha et al (2013) is to be replaced by …”

“…These quantities are then given as inputs to the polarized RT equation defined in Equation (1) of Smitha et al (2013). The expressions used to compute quantities such as the line and continuum source vectors, and their sum are same as Equations (5), (9), and (4) of Smitha et al (2013). The Stokes profiles are computed by solving the transfer equation perturbatively (see Faurobert 1987;Nagendra et al 2002).…”

“…A plausible reason for the failure of reproducing the rest intensity is the use of one-dimensional (1D) model atmospheres. In several earlier works, such as Holzreuter & Stenflo (2007), Shapiro et al (2011), Smitha et al (2013, and Supriya et al (2014), difficulties with the 1D models were encountered. The limitations of the 1D model atmospheres are also described in Kurucz (1997), Rutten (2002), and Uitenbroek & Criscuoli (2011).…”

Master equation theory applied to the redistribution of polarized radiation in the weak radiation field limit

“…Instead, Belluzzi & Trujillo Bueno (2013) for Na i and Anusha et al (2010) for Ca i resonance line, apply the M CO (also known as FAL-X) atmosphere model of Avrett (1995). Smitha et al (2013), who study Ba ii resonance line, elaborated on an even cooler atmosphere model than FAL-X. The FAL-X atmosphere model, already known to "give a good fit to the full range of mean CO line profiles, but conflic[ting] with other observations of average quiet regions" (Avrett 1995), is characterized by the fact that the temperature minimum occurs much higher than in VAL-C, at about 1000 km for FAL-X instead of 500 km for VAL-C.…”