Polarized line formation in spherically symmetric expanding atmospheres

Abstract

We consider the problem of polarized line formation in the spherically symmetric expanding atmospheres. The velocity fields in line forming regions produce Doppler shift, aberration of photons and also gives rise to advection. These in turn can modify the amplitudes and shapes of the emergent Stokes profiles. However, here we consider only non-relativistic regime, wherein mainly Doppler shift effects are significant. Thus only Doppler shift terms are considered in the polarized transfer equation. For the solution of the concerned polarized transfer equation we use the comoving frame formulation, and apply the Accelerated Lambda Iteration (ALI) method. We present the results by considering the scattering on a two-level atom, including the effects of partial frequency redistribution (PFR). The polarized line profiles are shown for few velocity laws, representative of expanding spherical atmospheres. It is shown that the degree of polarization in the lines depends sensitively on the extendedness R of the spherical atmosphere. We also present a comparison of polarized profiles computed under complete frequency redistribution (CFR) and PFR in the case of static as well as expanding atmospheres