Simultaneous Solution of Radiative Transfer Equation in the Comoving Frame and the Statistical Equilibrium Equation with Complete Redisribution

Abstract

Complete redistribution with Voigt profile function has been employed in obtaining the simultaneous solution of line transfer and the statistical equilibrium equation for a non-LTE two level atom in an extended stellar atmosphere expanding with spherical symmetry. We have taken the geometrical extension of the atmosphere to be 3 and 10 times the stellar radius. We also estimated the ratio of the number densities N2/N1 of the upper and lower levels assuming a velocity law in such a way that it always satisfies the equation of continuity. In the first iteration, we have set the upper level population N2 equal to zero. In the subsequent iterations this level gets populated considerably although it is still smaller than the equilibrium values. We have set e (the probability of photon destruction by collisional de-excitation) and beta (the ratio of continuum to line absorption coefficients) equal to zero in all the cases. We note that velocities do not influence the population densities of the levels as much as the combination of geometrical extension and gas motions.