Michelson interferometry with the Keck I telescope

We report the first use of Michelson interferometry on the Keek I telescope for diffraction-limited imaging in the near-infrared JHKL bands. By using an aperture mask located close to the f/25 secondary, the 10 m Keek primary mirror was transformed into a separate-element, multiple-aperture interferometer. This has allowed diffraction-limited imaging of a large number of bright astrophysical targets, including the geometrically complex dust envelopes around a number of evolved stars. The successful restoration of these images, with dynamic ranges in excess of 200:1, highlights the significant capabilities of sparse aperture imaging as compared with more conventional filled-pupil speckle imaging for the class of bright targets considered here. In particular, the enhancement of the signal-to-noise ratio of the Fourier data, precipitated by the reduction in atmospheric noise, allows high-fidelity imaging of complex sources with small numbers of short-exposure images relative to speckle. Multiepoch measurements confirm the reliability of this imaging technique, and our whole data set provides a powerful demonstration of the capabilities of aperture-masking methods when utilized with the current generation of large-aperture telescopes. The relationship between these new results and recent advances in interferometry and adaptive optics is briefly discussed.