Astrophysics and Space Science

, Volume 58, Issue 1, pp 189–205 | Cite as

Line formation in spherical media with partial frequency redistribution

I. Solution of the line transfer
  • A. Peraiah


The effects of partial redistribution of frequency on the formation of spectral lines in a static and spherically symmetric media have been investigated. The partial redistribution functionsRI andRII (Hummer, 1962) have been employed to calculate the lines for a two-level atom in non-LTE in a spherically symmetric medium with homogenous physical characteristics whose ratiosB/A (of outer to inner radii) are equal to 2 and 10. These results are compared with those formed in a plane-parallel medium withB/A=1. Two types of atmosphere are treated: (1) a pure scattering medium with ε=0 and β=0, and (2) an atmosphere with a constant source of emission ε=10−4 and β=0, where ε is the probability per scatter that a photon will be destroyed by collisional de-excitation and β is the ratioKc/Kl of opacity due to continuous absorption per unit interval of frequency to that in the line. Lines formed in complete redistribution also have been calculated for the sake of comparison, and the total optical depth in all cases has been taken to be 103 at the line centre.

Vast differences have been found between the lines formed by complete and partial redistribution functions (which, for the sake of simplicity, we shall hereafter refer to as CRD and PRD, respectively). In the case of a purely scattering medium, a small amount of emission is observed in the wings for all cases of scattering functions in the spherical medium as a result of the combined effects of curvature and physical scattering. In the scattering medium, more photons are scattered into the cores of the lines by PRD than in the case of CRD. The lines formed in the medium with internal sources show emission in all cases with small absorption in the cores, except those lines formed by the angle-dependent PRD functions which again depend on the geometrical extension of the medium.


Optical Depth Internal Source Partial Frequency Line Formation Continuous Absorption 
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Copyright information

© D. Reidel Publishing Company 1978

Authors and Affiliations

  • A. Peraiah
    • 1
    • 2
  1. 1.Institut für Theoretische Astrophysik der Universität HeidelbergHeidelbergGermany
  2. 2.Indian Institute of AstrophysicsBangaloreIndia

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