Resonance line transfer and transport of excited atoms—I. Basic relations and limiting cases

Full non–LTE spectral line formation

“…We believe that state-of-the-art iterative methods presently used for NLTE radiative transfer (see e.g., Lambert et al 2016, and references therein) will allow one to explore all of the potential of this alternative and a more detailed theoretical frame, beyond what could be achieved at that time by Borsenberger et al (1986Borsenberger et al ( , 1987 and Atanackovič et al (1987).…”

“…where Q 2 is a velocity-changing elastic collision rate. After Borsenberger et al (1986), one may consider Q 2 = n 1 v th. σ el.…”

“…(19), we are able to derive an explicit expression for the nonequilibrium VDF f 2 , assuming that all atoms in their fundamental state of energy follow a Maxwellian VDF, that is to say f 1 ≡ f M . As in Borsenberger et al (1986), we shall normalize the specific intensity to the "low temperature limit" of the Planck function, that is the Wien function:…”

“…This expression is indeed identical to Eq. (2.44) of Borsenberger et al (1986) when one neglects streaming of particles (his η = 0). Now, integrating Eq.…”

“…This general issue has already been discussed and summarized, mainly by Oxenius (1986; see also Oxenius & Simonneau 1994). However, so far and because of the inherent difficulty of the problem, only a few studies have already been conducted in the past (see e.g., Borsenberger et al 1986Borsenberger et al , 1987.…”