On the force associated with absorption of spectral line radiation
Abstract
The body force on stellar material produced when radiation is absorbed or scattered by atoms, that is, the force derived from the radiative tresses, is studied for the case in which the radiation is produced by line emission of a two4evel atom according to the mechanism of noncoherent scattering with complete redistribution. The force is considered for cases with either Doppler or Voigt absorption profiles in sstatic atmospheres with and without the effect of an overlapping continuum, and also in rapidly expanding atmospheres. Approximate analytic results are obtained in several asymptotic regimes. It is suggested that for static atmospheres the force is represented to order sofmagnitude accuracy by the result for LTE with the damping wings and sthe overlapping continuum omitted. This gives a simple relation, that sfor optical depths which are greater than unity in the line, but less sthan unity in the continuum, the force varies as the inverse of the soptical depth. The force due to the line alone is very small for optical sdepths greater than unity in the continuum. In rapidly expanding satmospheres the force is also represented by this formula, except that sthe optical depth takes the velocity gradient into account. A sconsequence of these relations is that the force due to an optically sthick line is independent of the strength of the line.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 November 1974
 DOI:
 10.1093/mnras/169.2.279
 Bibcode:
 1974MNRAS.169..279C