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Abstract
The infrared properties of the circumstellar shells surrounding several OH/IR stars are investigated using photometry and high-resolution imaging techniques. From Continuous Variable Filter photometry at 2 microns, strong CO and moderate H(,2)O absorption have been detected in a number of recently identified OH/IR stars implying that they are Mira-type variable stars undergoing extensive mass loss. The color temperatures derived from this data at 2 microns range from 500(DEGREES)K to 800(DEGREES)K. Filter photometry from 2 to 20 microns implies color temperatures in the 10 micron region ranging from 400(DEGREES)K to 600(DEGREES)K showing that the effective temperature decreases with increasing wavelength. The absorption feature at 10 microns is found to vary from source to source. The assumption that the 10 micron feature is intrinsic to the sources and due to opacity effects within the shell is investigated and found to be consistent. The high-resolution technique of speckle interferometry combined with the Knox-Thompson image recovery algorithm is compared with that of the shift-add technique. In most cases the results from the two methods are similar although Knox-Thompson appears to have a better resolution capability while shift-add has a much better signal-to-noise ratio. The reconstructed images are dominated by a strong unresolved central source surrounded by a diffuse partially resolved shell. The wavelength dependence of the size of the emitting region and the ratio of the flux from the shell to the central component is found. The diameters are proportional to the wavelength of observation and the relative contribution of the shell increases with wavelength also. The infrared observations, when compared with the radio OH maps obtained from the VLA, imply a bipolar mass outflow. If the model of a bipolar outflow is correct, then it appears that the infrared observations detect the polar lobes while the OH emission is confined to the equatorial region.
