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

The paper starts from the rationale, already presented in 2004 at the first Toulouse meeting on astronomy at Dome C, to propose an infrared, wide-field Imaging FTS (IFTS) as a first generation instrument behind a 2 to 3 m optical telescope. Such an instrument could fully take advantage of all the properties of the site for imagery and spectroscopy and offer an instrument presently needed after the numerous imaging surveys. Simulations have been conducted to define the range of field size and of resolution which could be reachable. Then, derived from the study of H2 Explorer (H2EX) an IFTS for 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 ouput interferometer, using cat's eyes retroreflectors in its arms. With a maximum optical path difference (OPD) of 30 cm a spectral resolution of 105 at 2 μm (20 000 at 25 μm) is possible with this field size, behind a PILOT-type telescope (2.4 m) and a minimum beam size of 80 mm within the interferometer. With the same optics and the same mechanism of control of the OPD, two interchangeable beamsplitters (2 to 5.5 μm and 6 to 25 μm) and the corresponding detector arrays (InSb and Si:As) cover the entire spectral range. The instrument must be cryogenic (temperature around 50 K) to make the thermal background from the optics negligible. The best sensitivity is obtained through narrow-band filters (2%) isolating lines in emission-line regions. Such a survey instrument has never been built before. It calls for a dedicated telescope for the best use of this type of instrument on the Dome C site