Near-LTE Linear Response Calculations with a Collisional-Radiative Model for He-like Al Ions

This paper establishes a connection between atomic kinetics and nonequilibrium thermodynamics, using a collisional-radiative model modified to include line absorption. Steady-state emission is calculated for He-like aluminum immersed in a specified radiation field having fixed deviations from a Planck spectrum. The calculated net emission is presented as a NLTE response matrix. In agreement with a rigorous general rule of nonequilibrium thermodynamics, the linear response is symmetric. We compute the response matrix for 1% and ±50% changes in the photon temperature and find linear response over a surprisingly large range. copyright 1998 The American Physical Society