Abstract
Future astronomical space missions will comprise a constellation of several optical telescopes to detect exo-planets by interferometric nulling of starlight. The Darwin mission of the European Space Agency (ESA) and NASAs Terrestrial Planet Finder Interferometer both consist of a free-flying collection of telescopes and a beam combiner. As such, the constellation provides a co-phased array of telescopes that can also be used for aperture synthesis imaging. This imaging technique relies on recording intensity interference patterns, in which the layout of the beam combination optics and the detector play a key role. Several designs for beam combination have been proposed in the literature. In this article, we compare these beam combiners by rigorously simulating the imaging process of a weak stellar source, taking into account the photon arrival statistics, an imperfect detection process and the image reconstruction from the recorded data. The results are presented as the to be expected reconstruction error in the luminous intensity distribution function of a wide-field stellar source versus the provided amount of photons. Using these results, the optimum design of the combination beam combiner and detector array can be identified.
Highlights
With successful optical stellar interferometers in operation on Earth, stellar interferometry has proven to be a valuable observation technique [1]–[3]
Two or more telescopes observe the same source and, by coherent combination of the collected radiation, information is gained about the source with an angular resolution directly related to the separation of these telescopes, rather than the diameter of a single telescope
The Darwin mission of the European Space Agency (ESA) aims at such a constellation of telescopes [4]. Another space-based interferometer will be the Terrestrial Planet Finder Interferometer or TPF-I by NASA. The value of these missions can be greatly expanded by the addition of an imaging mode, allowing aperture synthesis imaging next to the nulling task [5]
Summary
With successful optical stellar interferometers in operation on Earth, stellar interferometry has proven to be a valuable observation technique [1]–[3]. The Darwin mission of the European Space Agency (ESA) aims at such a constellation of telescopes [4] Another space-based interferometer will be the Terrestrial Planet Finder Interferometer or TPF-I by NASA. Unlike the practice in radio astronomy, the selection of a single frequency is impossible and noise-free amplification of collected electro-magnetic fields at each telescope does not exist. The goal is to image a field possibly as large as that of a single telescope having the resolution of the interferometer array. It is our goal to treat all interferometers, or rather the beam combiners that identify them, as optical imagers This allows coverage of polychromatic observations as well as wide-field interferometry in a straightforward manner. The assumed and collected spectrum is broad banded, but constant over the source
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