Apparent Sizes and Spectral Line Profiles for Spherical and Disk Masers: Solutions to the Full Equations

Calculations are performed for the spectral line profiles and images ofastrophysical maser radiation that emerges from isolated spheres and thin disksviewed edge-on. In contrast to previous investigations where variousapproximations are made, the full equations are solved here for thefrequency-dependent radiative transport that includes the thermal motion of themolecules. The spectral line profiles for spheres and disks are found torebroaden to the full thermal Doppler breadth with increasing saturation inessentially the same way as is well known to occur for a linear maser. Thevariation with frequency in the apparent angular sizes of masing spheres andthin disks is found to be negligible at frequencies within the spectral linewhere the flux is significant. Calculations also are performed for sphericaland disk masers that are not isolated, but for which the seed radiation for themasers is incident from one side as would occur when a strong continuum sourceis on the far side of the masers. Again, the spectral line profiles are foundto rebroaden to the full thermal breadths with increasing saturation and thereare no significant variations in the apparent angular sizes with frequency.However, the full rebroadening does occur at somewhat higher saturation and thevariation of the apparent angular sizes as a function of the degree ofsaturation is quite different from that of the isolated masers. Spheres anddisks have served as idealized geometries with which to examine possibledeviations from the linear approximation for astrophysical masers.Comment: accepted for Astrophysical Journa