## 2. Basic expressions## 2.1. Monochromatic radiation flux
The monochromatic flux vector at
depth is obtained by integration
over all directions (I:12) from the flux
in the direction with being the corresponding static value, so that the correction (I:44) for the inclusion of a velocity field is Here is the monochromatic extinction coefficient, the corresponding spectral thickness (I:37) with , the spatial derivative (I:6) of the the Planck function for the temperature at depth , and the weighting function (I:8) entering the Rosseland mean opacity. is the wavelength integrated Planck function, and ( Stefan-Boltzmann constant). As has been shown in Sect. 5 of Paper I, other radiative quantities of interest, in particular the monochromatic radiative acceleration (I:16), as well as the wavelength-integrated expressions (I:11,15) can be derived from the monochromatic flux. ## 2.2. Extinction coefficient
The extinction coefficient copmprising absorption and scattering - can
be written in the with being the strength of the
line For the profile function we may
choose either Lorentz respectively. If the line is sufficiently narrow, i.e. if the relevant distances from the line center are not too large, the profile functions are obtained from the conventional profiles by utilizing (cf. Appendix B of Wehrse et al. 1998); furthermore and where and are the usual damping constant and Doppler width, respectively, in the ordinary wavelength scale. In astrophysical applications one frequently has to treat a © European Southern Observatory (ESO) 2000 Online publication: July 7, 2000 |