Bibcode
DOI
Bellot Rubio, L. R.; Ruiz-Cobo, B.; Collados, M.
Referencia bibliográfica
The Astrophysical Journal, Volume 506, Issue 2, pp. 805-817.
Fecha de publicación:
10
1998
Revista
Número de citas
40
Número de citas referidas
31
Descripción
Spectral synthesis calculations in stellar (magnetized) atmospheres are
based on the solution of the radiative transfer equation (RTE) for
polarized light. The thermodynamic and magnetic properties of the
atmospheres, along with the radiation field, completely specify the
basic ingredients of the RTE, after which numerical methods have to be
employed to calculate the emergent Stokes spectra. The advent of
powerful analysis techniques for the inversion of Stokes spectra has
evidenced the need for accurate and fast solutions of the RTE. In this
paper we describe a novel Hermitian strategy to integrate the polarized
RTE that is based on the Taylor expansion of the Stokes parameter vector
to fourth order in depth. Our technique makes use of the first
derivatives of the absorption matrix and source vector with respect to
the coordinate measured along the ray path. Both analytical and
numerical results indicate that the new strategy is superior to other
methods in terms of speed and accuracy. It also gives an approximation
to the evolution operator at no extra cost, which is of interest for
inversion algorithms based on response functions. The Hermitian
technique can be straightforwardly particularized to the scalar case,
providing a very efficient solution of the RTE in the absence of
magnetic fields. We investigate in detail the consequences of the
oscillations that appear in the evolution operator for large values of
line strength eta_0. The problems they pose are shared by all
integration schemes, but can be minimized by adopting nonequally spaced
grids.