T-ReCS Introduction

T-ReCS is a mid-infared (8-26µm) imager and low-resolution (R=100-1000) spectrograph for use on Gemini South. It is under construction at the University of Florida. The current estimate for delivery of T-ReCS to Gemini Observatory is 2nd quarter 2001 (estimate updated 3-Feb-2000). There will be a period of characterisation and commissioning after delivery before it will be available for scientific use.

The low emissivity and high Strehl thermal infrared imaging capabilities of the Gemini telescopes will lead to very effective use of mid-infrared instruments. The imager, presently under construction at the University of Florida, is foremost intended to be a relatively simple camera dedicated to high performance imaging. The highest design priority for the instrument is broad-band 10 µm imaging. Such an imager, when combined with Gemini's fast tip/tilt compensating secondary mirror, should yield nearly diffraction limited 10 µm images under most natural seeing conditions. The imager must therefore be able to exploit the high background characteristics of state-of-the-art mid-infrared arrays. It is expected that a Si:As IBC array with a format approximating ~256x256 will be incorporated into the imager, offering coverage from ~5 to 25 µm. A single plate scale of 0.09 arcsec/pixel will be used to critically sample a diffraction limited 10 µm point source PSF. Furthermore, high throughput is a premium in the instrument design, in order to take full advantage of the coatings used in the telescope optics. Like all of the infrared instruments, the imagers contribution to the total system emissivity must be kept as low as possible to exploit the ~2% telescope emissivity, and the instrument specification requires <1% effective emissivity (including ghosting, scattering, radiation leaks, etc.). A filter capacity of ~20-30 filters will be needed to supply users with an adequate complement of broad and narrow band filters.

Unlike the other infrared instruments, the mid-infrared imager will not have an on-board wavefront sensor due to the lack of dichroic availability that can effectively pass visible radiation and reflect infrared radiation across such a broad thermal band. Luckily, running the imager without an on-board sensor should not significantly degrade its performance since the A&G units peripheral sensors should be able to provide adequate tip/tilt correction, i.e., the size of the isoplanatic patch is large enough at 10 µm that an off-axis wavefront sensor can be used for atmospheric compensation.

For information on capabilities, performance and system verification status see the contents list.

Last update March 21, 1999; Phil Puxley