non-LTE Radiative Transfer Research Articles

Time-dependent aerodynamic non-LTE radiative transfer

A method is developed for solving simultaneously in one dimension the equation of transfer for non-LTE spectral line radiation and the time-dependent equations specifying conservation of mass, energy and linear momentum. In particular, we illustrate the method on a ‘simple’ time-dependent problem in which a pulsating disturbance at some point in a model homogeneous atmosphere propagates towards the surface and steepens into a shock. The resulting emergent intensities show rather dramatic changes over very small time intervals due to the effect of the velocity, density and temperature distributions on the radiative absorption properties of the gas, and thus emphasises the need to solve the above-mentioned four basic equations if one is to obtain physically realistic model atmospheres experiencing initial disturbances.

Formation of the solar H? profile

A series of non-LTE radiative transfer solutions for Hα was computed using the integrodifferential equation technique of Athay and Skumanich (1967). A model hydrogen atom consisting of three bound levels and a continuum was assumed. It was found that increasing the temperature of the chromosphere at the height of line formation decreases the central intensity of the line. The density structure of the atmosphere primarily affects the optical depth scale rather than the source function. The temperature minimum region of the atmosphere was found to be transparent to Hα radiation, so that the radiation in some part of the line will arise from two distinct layers of the atmosphere, one above the temperature minimum and one below it. The computed Hα profile was found to be highly sensitive to the assumed 2–3 collisional cross-section.