Resolving the Future of Astronomy with Long-Baseline Interferometry

We discuss the status of coherent integration with the Navy Prototype Optical Interferometer (NPOI) Armstrong et al. (1998). Coherent integration relies on being able to phase reference interferometric measurements, which in turn relies on making measurements at multiple wavelengths. We first discuss the generalized group-delay approach, then the meaning of the resulting complex visibilities and then demonstrate how coherent integration can be used to perform very precise measurement of stellar diameters. The phase of the complex visibility is particularly attractive as a data product because it is not biased in the same way that visibility amplitudes are. We demonstrate how single-baseline phases can be used to make accurate measurements of magnitude differences and separations of binary stars.