Design of a Wide-Field Imaging FTS at High Spectral Resolution for Dome C

Abstract

The paper starts from the rationale, already presented in 2004 at the firstToulouse meeting on astronomy at Dome C, to propose an infrared, wide-fieldImaging FTS (IFTS) as a first generation instrument behind a 2 to 3 moptical telescope. Such an instrument could fully take advantage of all theproperties of the site for imagery and spectroscopy and offer an instrumentpresently needed after the numerous imaging surveys. Simulations have beenconducted to define the range of field size and of resolution which couldbe reachable. Then, derived from the study of H₂ Explorer (H2EX) an IFTSfor a space project, an optical design for a 2 to 25 μm instrument,imaging a 10'×10' field, has been developed, based on a dual ouputinterferometer, using cat's eyes retroreflectors in its arms. With amaximum optical path difference (OPD) of 30 cm a spectral resolution of10⁵ at 2 μm (20 000 at 25 μm) is possible with this fieldsize, behind a PILOT-type telescope (2.4 m) and a minimum beam size of80 mm within the interferometer. With the same optics and the samemechanism of control of the OPD, two interchangeable beamsplitters (2 to5.5 μm and 6 to 25 μm) and the corresponding detector arrays (InSband Si:As) cover the entire spectral range. Theinstrument must be cryogenic (temperature around 50 K) to make the thermalbackground from the optics negligible. The best sensitivity is obtainedthrough narrow-band filters (2%) isolating lines in emission-lineregions. Such a survey instrument has never been built before. It calls fora dedicated telescope for the best use of this type of instrument on theDome C site.