Apparent Sizes and Spectral Line Profiles for Spherical (``Threedimensional'') Astrophysical Masers
Abstract
Calculations are performed for the frequencydependent transport of radiation in a uniform spherical maser. Coupling between the intensities at different frequencies is treated. Spherical masers are commonly utilized as idealized geometries in which to assess possible deviations (sometimes, 'threedimensional effects') from the approximation of a linear geometry. We find that the spectral line profile rebroadens in approximately the same manner as that for a linear maser so that the relationship between the line breadth and the luminosity, beaming angle, and degree of saturation is essentially unchanged. The variation of the apparent size of a spherical maser with frequency is not found to be significant at frequencies within the line profile at which the intensity is appreciable. The 'standard approximation' is adequate for obtaining most of the basic properties of spherical masers that have been examined including the relationship between the pumping (or molecular populations) and the intensity of maser radiation. The improved methods employed here are, however, necessary to obtain variation of the apparent size with frequency in the saturated regime. These conclusions differ from those of previous investigators. The calculations here are more reliable than those of previous investigators because these are selfconsistent and avoid certain inaccurate simplifications.
 Publication:

The Astrophysical Journal
 Pub Date:
 April 1994
 DOI:
 10.1086/173950
 Bibcode:
 1994ApJ...424..991E
 Keywords:

 Astronomical Models;
 Frequencies;
 Interstellar Masers;
 Line Shape;
 Line Spectra;
 Population Inversion;
 Radiation Transport;
 Spherical Plasmas;
 Angles (Geometry);
 Approximation;
 Luminosity;
 Luminous Intensity;
 Maser Pumping;
 Saturation;
 Size (Dimensions);
 Astrophysics;
 LINE: PROFILES;
 MASERS