Limiting magnitude of reference source for separate element interferometry

Astronomical imaging from Michelson interferometers with separated elements has been demonstrated by a number of authors (e.g. Young et al. (2003); Baldwin et al. (1996); Monnier (2003); Burns et al. (1997)). The principles of the technique are the same as bispectral analysis of images taken through non-redundant aperture masks at a single telescope as described above. Each telescope in a separate element interferometer array is equivalent to one subaperture of the aperture mask. In separate element interferometers the light is often combined using half-silvered mirrors in a pupil-plane as shown in Figure 1.7, rather than in an image plane. With no active wavefront correction on the individual telescopes and photon-counting detectors the limiting magnitude for this method is similar to that of bispectrum imaging at single telescopes. All existing and planned separate-element interferometers have some form of adaptive optics correction (often only the image position or tip-tilt component). The limiting magnitude of reference source required for adaptive optics correction sets an upper limit on the limiting magnitude for these arrays, and this is discussed in the next section.

Figure 1.7: Schematic showing pupil-plane beam combination in a two-telescope optical interferometer.