Polarization Properties of Astrophysical Masers

Citation

Kwan, John Ying-Kuen (1973) Polarization Properties of Astrophysical Masers. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/906J-2N21. https://resolver.caltech.edu/CaltechTHESIS:08252017-145131867

Abstract

Observed interstellar OH and H₂O maser lines at 18 cm and 1.35 cm exhibit unusual polarization properties. The OH emitters with the highest brightness temperatures, usually associated with H II regions, almost always show a high degree of circular polarization. The H₂O maser line, on the other hand, is rarely polarized, and then only linearly polarized.

The preference for circular polarization in the brightest OH sources was attributed by Litvak to the mechanism of parametric down-conversion. In this process the higher-frequency components of a Zeeman split maser line are down-converted to lower-frequency components and to an electron cyclotron wave. This mechanism is shown to be too weak to be of importance in astrophysical masers.

The polarization properties of the OH and H₂O masers are related to the physical conditions in the maser clouds. It is found that the magnetic field, the plasma, and trapped infrared lines in maser sources play an important role in determining the polarization on the emitted radiation.

Thesis Files