Abstract

A stellar interferometer involving two movable telescopes is in use on Mount Wilson in the 10 m atmospheric window. Baselines between 4 m and 35 m have been laid out but observations so far have been with baselines of 4 m and 13 m. Heterodyne detection and lobe rotation are used as they are in a radio interferometer, with frequency of the resulting interference fringe reduced to a fixed 10 Hz. Fluctuations of the fringe frequency about the central 10 Hz frequency are measured, along with fluctuations of the 11 m optical paths within each telescope. The spectrum of each of these fluctuations is calculated, as is the spectrum for transmission in the atmosphere excluding the internal optical path. For a 4 m baseline and reasonably good seeing 2", the relative optical paths are stable enough to provide no change in average frequency for observation times of as long as 1 h, which produces a fringe signal width of ~0.3 mHz with small modulation sidebands. Atmospheric path-length fluctuations at frequencies between ~1 and ~10^-3 Hz are obtained from the sidebands or from measured phase fluctuations. Wide variations in characteristics of the power spectrum occur for various atmospheric conditions.

© 1990 Optical Society of America