Diffraction-limited imaging. II - Optical aperture-synthesis imaging of two binary stars

Abstract

The technique of nonredundant masking at the Hale 5-m telescope and radio VLBI imaging software are used to make optical aperture-synthesis maps of two binary stars, Beta Corona Borealis and Sigma Herculis. The dynamic range of the map of Beta CrB is about 50:1. For Sigma Her, a separation of 70 milliarcsec is found. These maps demonstrate the potential of the nonredundant masking technique for diffraction-limited imaging of astronomical objects with high dynamic range. The optimal integration time for measuring the closure phase is found to be longer than that for measuring the fringe amplitude. There is not a close relationship between amplitude errors and phase errors, and amplitude self-calibration is less effective at optical wavelengths than at radio wavelengths.