DIFFERENTIALLY MOVING-MEDIA WITH MANY SPECTRAL-LINES - STOCHASTIC APPROACH

Based upon the analytical solution of the radiative transfer equation for a given source function and a new approach to account for very man y spectral lines contributing to the extinction, the connection betwee n line properties and the emergent intensity is derived under the assu mption that the wavelengths of the line centers follow a Poisson point process, whereas the other line parameters may have arbitrary distrib ution functions. A comparison with the widely used list of Kurucz show s that the Poisson distribution well describes deterministic ''real'' lines. The presentation by a Poisson point process requires only a mod est number of parameters and is very flexible. It allows most operatio ns to be carried out analytically and hence is very suitable to study the intricate influence of many lines on radiation fields in different ially moving media. We consider a simplified case of the solution of t he radiative transfer equation in order to demonstrate the basic effec ts of the velocity field upon the emerging radiation field. Expression s for the expectation value of the intensity are derived, and examples are given for Lorentz line profiles and infinitely sharp lines, in pa rticular as functions of the velocity gradient and the mean line densi ty. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.