Twenty Years of Speckle Interferometry

Extract

The purpose of my talk is to briefly review the results of two decades of astrometric research using the technique of speckle interferometry. Although speckle, invented by Labeyrie in 1970 (Gezari et al. 1972), is the most well–known and widely–used interferometric technique in the visible and near infra-red, it neither the only technique in use, nor was it the first. Karl Schwarzschild made the first interferometric measurements of binary stars in 1895, using the then–new technique of Michelson interferometry and following a suggestion by Michelson himself that his technique was amenable to binary star astrometry. From 1919 to 1921, Anderson (1920) and Merrill (1922) made a series of measurements of Capella and other bright stars, using a Michelson interferometer of 20-foot baseline, mounted on the Mount Wilson 100-inch. These early measurements have definitely stood the test of time. Figure 1 shows a recently calculated orbit of Capella (Bagnuolo & Hartkopf 1989), using data spanning some 250 full revolutions. Anderson and Merrill’s measurements agree beautifully with observations made 7 decades later. As a result, Capella has probably the most accurately known orbit of any visual binary. Orbital elements calculated in 1981 (McAlister 1981) and again 10 years later differ in period by about 14 seconds, or less than 2 parts per million!