Radiative transfer in cylindrical threads with incident radiation

V. 2D transfer with 3D velocity fields

Institut d'Astrophysique Spatiale, Univ. Paris XI/CNRS, Bât. 121, 91405 Orsay Cedex, France e-mail: pierre.gouttebroze@ias.u-psud.fr

Received: 19 December 2007
Accepted: 28 April 2008

Abstract

Context. Time-resolved observations of loops embedded in the solar corona show the existence of motions of matter inside these structures, as well as the global motions of these objects themselves.

Aims. We have developed a modeling tool for cylindrical objects inside the solar corona, including 2-dimensional (azimuth-dependent) radiative transfer effects and 3-dimensional velocity fields.

Methods. We used numerical methods to simultaneously solve the equations of NLTE radiative transfer, statistical equilibrium of hydrogen level populations, and electric neutrality. The radiative transfer equations were solved using cylindrical coordinates and prescribed solar incident radiation. In addition to the effects of anisotropic incident radiation, treated in previous papers, we took into account the Doppler shifts produced by a 3-dimension velocity field.

Results. The effects of different types of velocity fields on hydrogen line profiles and intensities are described. Motions include loop oscillations, rotation, and longitudinal flows, which produce different deformations of profiles. Doppler brightening and dimming effects are also observed.

Conclusions. This is a new step in the diagnostic of physical conditions in coronal loops, allowing the study of dynamical phenomena.