The Time Development of a Resonance Line in the Expanding Universe
Abstract
The timedependent spectral profile of a resonance line in a homogeneous expanding medium is studied by numerically solving an improved FokkerPlanck diffusion equation. The solutions are used to determine the time required to reach a quasistatic solution near the line center. A simple scaling law for this relaxation time is derived and is fitted to the numerical results. The results are applied to the case of Lyman alpha scattering during primordial recombination of hydrogen. For a wide range of cosmological models it is found that the relaxation times are smaller than the recombination timescale, although not by a very large factor. Thus the standard assumption of a quasistatic solution in cosmological recombination calculations is reasonably valid, and should not cause substantial errors in the solutions.
 Publication:

The Astrophysical Journal
 Pub Date:
 June 1994
 DOI:
 10.1086/174170
 arXiv:
 arXiv:astroph/9312006
 Bibcode:
 1994ApJ...427..603R
 Keywords:

 Astronomical Models;
 Expansion;
 FokkerPlanck Equation;
 Hydrogen Recombinations;
 Lyman Alpha Radiation;
 Numerical Analysis;
 Radiative Recombination;
 Relaxation Time;
 Resonance Lines;
 Universe;
 Coherent Scattering;
 Cosmology;
 Diffusion Theory;
 Inflating;
 Astrophysics;
 COSMOLOGY: THEORY;
 LINE: FORMATION;
 Astrophysics
 EPrint:
 20 pages text and 10 figures, in 30 pages of uuencoded, compressed postscript. CFA preprint no. 3753