EMCCD Speckle Interferometry at the U.S. Naval Observatory

The United States Naval Observatory (USNO) has conducted a speckle interferometry program using intensified CCDs (ICCD) on the 26-inch refractor since 1990. Charged with obtaining accurate and precise measurements of bright, modest separation double stars that have been neglected by other programs, the USNO speckle program has published over 32,000 measurements of double stars. Following the failure of the most recent ICCD in 2019 and the successful implementation of electron-multiplying CCDs (EMCCD) in other speckle programs, USNO obtained an EMCCD and manufactured a new camera head for use with the 26-inch telescope. We present the specifications, calibration, and characterization of the new speckle camera, as well as results from the first 1.5 years of operation. Between 2020 July and 2021 December nearly 5000 observations of double stars were made with the EMCCD speckle camera. In addition to the angular separation and position angle measures routinely determined by the speckle program, the EMCCD now allows for the measurement of magnitude differences between components. The improved signal-to-noise for fainter targets and larger limiting magnitude of the EMCCD has also increased the number of systems accessible with the 26-inch by approximately 150%.