**Caption:** Simulation of how the binary system shown in the previous
figure would appear on the detector of an interferometer-spectrograph
combination with 20 cm apertures separated by 3 meters (these parameters
correspond to the initial configuration for *ELFS*). The simulation
assumes that the separation of the two components of the binary is 5
milli-arcsec, that the observation is taken at maximum separation, and that
the point spread function in the dispersion direction is a delta-function (a
reasonable approximation of *ELFS* beam, which is highly compressed in
the dispersion direction). The pattern has been normalized to unity
at each wavelength for display purposes. The vertical lines indicate the
locations of the individual components. Notice how distinct the shift in
the centroid as a function of wavelength appears, even though the binary
is not resolved at any given wavelength. Because the centroid is dominated
by the cool component at the longest wavelengths and the hot component at
the shortest ones, the wavelength dependence of the centroid provides an
unambiguous measure of the angular separation of such a system.