Aperture Synthesis at Optical Wavelengths

Abstract

Optical stellar interferometers have demonstrated milli-arcsecond resolution with few apertures spaced tens of meters apart. Results from the area of stellar angular diameters with implications for emergent fluxes, effective temperatures, luminosities and structure of the stellar atmosphere, dust and gas envelopes, binary star orbits with impact on cluster distances and stellar masses, relative sizes of emission-line stars and emission region, stellar rotation, limb-darkening, and astrometry have been published. However, in order to obtain snapshot images, many-apertures would be required, for a better sampling of the incoming wavefront. The coherent imaging thus achievable improves the sensitivity with respect to the incoherent combination of successive fringed exposures, heretofore achieved in the form of optical aperture synthesis. For efficient use of a multi-aperture imaging interferometer, this can be done with pupil densification, a technique also called hypertelescope imaging. When equipped with a coronagraph, this can be used for imaging of exo-planet transits across a resolved star. The capabilities of such a technique can be envisaged through a simulated image carried out recently by Surya et al. [1]. This lecture is aimed to describe some of these techniques and methods.