Experimental Tests of the Astrometric Precision Obtainable with a Ten Micron Interferometer.

The purpose of this project was to test whether the relative positions of stars could be measured with an infrared spatial interferometer to high accuracy--that is, 0.1 seconds of arc or better. For such a test, a number of measurements were made on the relative hour angles of three stars, omicron Ceti, alpha Orionis, and R Leonis, each separated by about 50 deg. About ten measurements of omicron Ceti and alpha Ori were made each night for 10 nights during a two-week period. The RMS deviation between measurements on a single night was approximately .07 arc seconds and the RMS variation from night to night among the 10 different nights was 0.08 arc seconds. Similar but less extensive results were obtained on R Leonis. This night-to-night positional accuracy is somewhat better than is normally achieved with the best optical techniques, and clearly of value for the Navy's task of assembling accurate stellar positions. The errors encountered appear to be largely due to mechanical instability of the telescopes used. These telescopes were not designed for astrometry, and had both bearing variations and temperature distortions which are estimated to be comparable with the errors found. Errors due to atmospheric seeing appeared to be substantially smaller than these. We believe this series of tests successfully achieved its objective and demonstrated the usefulness of infrared spatial interferometry for very precise astrometric measurements over large angular separations. (Author)