Speckle imaging produces diffraction-limited images from ground-based telescopes in the optical wavebands. While the technique dates back almost 50 years, recent advancements in detectors such as electron-multiplying CCDs (EMCCDs) have spawned a resurgence of this technique. The use of EMCCDs has greatly improved sensitivity and observing efficiency for speckle instruments. The high angular resolution provided by speckle imaging can discern blended binary system contamination and validate suspected exoplanets discovered by the Kepler, K2, and TESS transit surveys. Three speckle instruments have been built to this purpose: one at the WIYN telescope, one at Gemini-North, and one at Gemini-South. These instruments are supported by NASA's Exoplanet Program Office and available for the community via the proposal process for each telescope. Multiplicity can be determined along with separation, position angle, photometry, and contrast ratio in a single observation. The speckle instruments can observe over a hundred targets per night and resolve binary systems only tens of milli-arcseconds apart in two wavebands simultaneously. In this way speckle imaging can validate even small, rocky planets like TRAPPIST-1 and constrain exoplanet radii and density. Observing in multiple wavelengths may further characterize observed systems. Furthermore, the high-speed capabilities and sensitivity of EMCCDs opens up new regimes for time-series photometry of rapidly varying astronomical sources.
A brief history of speckle interferometry
Why EMCCDs have revitalized speckle techniques
Current speckle projects and science
Other benefits and uses of EMCCDs with speckle imagers.
Obtain overview of Andor camera solutions for high speed astronomical imaging
Date: May 2020
Author: Dr Nic Scott, Research Scientist, NASA Ames Research Center & Dr Ines Juvan-Beaulieu, Astronomy Specialist, Andor Technology