The imaging mode of the InfraRed Space Interferometer IRSI-Darwin

摘要

ESA's DARWIN will be an interferometric mission carrying out high-resolution astrophysical observations as well as the detection/characterization of earthlike exoplanets. In this paper, the current status and development perspectives of the Darwin imaging mode are discussed. First, overall system aspects are addressed including expected sensitivity, and baseline reconfiguration needs. Subsequently, the current instrumental concept is reviewed. This is based on a phase-referencing architecture supporting simultaneous observation of the science object, and an off-axis reference target for OPD stabilization purposes. The reference and science beams are wavelength-multiplexed and propagate along a common path through the interferometer. The viability of the cophasing approach is discussed, with emphasis on crosstalk control for multiplexed beam transfer, real-time compensation of the astrometric OPD, and associated metrology requirements. Studies have shown that imaging capabilities can be implemented within the current nulling beam combiner concept, which avoids the complexity and cost of developing a dedicated imaging beam combiner spacecraft. However, this approach has important drawbacks for the imaging mission including (ⅰ) a much lower sensitivity than achievable for a beam combiner specifically designed for imaging, and (ⅱ) a small field of view of a few tenths of arcsecond. A preliminary concept is presented of a dedicated, wide-field imaging beam combiner for Darwin based on homothetic mapping. Requirements, expected performance, technology development needs, and current activities in this area are discussed.