Infrared and Microwave Variability of OH/IR Stars and a One Millimeter Wavelength Detecting System for the 200-inch Telescope

Citation

Harvey, Paul Michael (1974) Infrared and Microwave Variability of OH/IR Stars and a One Millimeter Wavelength Detecting System for the 200-inch Telescope. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/gtra-vm48. https://resolver.caltech.edu/CaltechTHESIS:06022021-182426993

Abstract

This thesis consists of two distinct parts, an observational section concerned with the variability of OH/IR stars, and an instrumental section describing the development and calibration of a 1 mm detecting system.

In the first part systematic observations are presented for 14 OH/IR stars. Many of the sources show clear periodic variations between 1 and 10μ and at 1612 MHz with no observable phase difference between the infrared and microwave. The best explanation for this correlation seems to be that the OH masers are radiatively pumped. In at least two sources the 1665/1667-MHz variations are significantly greater and more random than the 1612-MHz variations. The data are not of sufficient quality to determine if the 1665/1667-MHz and infrared variations are correlated. No evidence is seen in the infrared for periodic variations of the color temperatures of the circumstellar dust shells which are believed to surround many of these stars. For the Mira stars observed, a correlation exists between the period of variation, the amplitude of variation at 2.2μ, the [3.5μ] - [10μ] color index, the separation in velocity of the two OH emission features, and the existence of 1.35 cm H₂O emission.

The 1 mm detecting system described in the second part of this thesis utilizes a germanium bolometer as the detecting element. Various filter materials -- glass fiber impregnated teflon, black polyethylene, a wire mesh in reflection, the atmosphere, and diffraction effects -- combine to limit the bandwidth of the system to the approximate range of 0.8 mm to 2 mm. A dual beam chopper is employed with a beam separation of 2.3 arcminutes and a half-power beamwidth of 1.7 arcminutes. The absolute and relative calibrations of the system are based on assumed planetary brightness temperatures. The sensitivity of the calibration to changes in atmospheric conditions and to differences in source spectra is investigated, and the sample calibration of several observations is described for illustration.

Thesis Files