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This paper deScribeS the design of an infrared Cold Coronagraph (CoCo) built for use at the NASA 3-rn Infrared Telescope Facility (IRFF) at Mauna Kea Observatory for the imaging of faint infrared sources in proximity to bright sources. The coronagraph is designed to obtain high contrast photometric images by use of an occulting mask and a pupil mask. The coronagraph is to be used in combination with the 111ff NSFCAM, which covers 1-5 jim and uses a 256x256 InSb array. The platescale can be varied from 0.06"/pixel to 0.1 5/ucl. covering a field of view of 14" and 38", respectively. Selectable apodized and hard occulting masks are mounted an a ibed as the first element in the system to reduce scattered light. Selectable pupil masks are cooled to 77K within tbe ('Co cryostat. The cryostat consists of a liquid nitrogen can for cooling the optics, masks, and baffles. The CoCo dewar is mounted on a slide in a housing to allow it to move out of the beam path so that the NSFCAM may be used with or without the coronagraph during the same observing period.

ABSTRACT. Using a new f/31 secondary on a tip-tilt platform, we have built an image-stabilization system which has been used regularly for astronomical imaging and spectroscopy on the University of Hawaii 2.2 m telescope. Di †raction-limited cores of stellar point-spread functions are achieved in nearinfrared imaging, with Strehl ratios as high as 0.47. K-band images with FWHM resolution (without 0A .3 deconvolution) are routinely obtained. The construction, operation, and capability of the current system are described, a summary of recent scientiÐc Ðndings is presented, and future improvements are outlined.

The upgraded 3.8m UK Infrared Telescope (UKIRT) is now provided with:. Tip-tilt image stabilisation by a light-weighted secondary mirror on piezo-electric actuators, controlled by a fast guider sampling at 40 Hz on guide stars V 18.m6;. Active primary mirror figure and secondary mirror alignment control, via a regularly-maintained look-up table (LUT);. Active focus measurement and correction by the fast guider, supplementing a focus maintenance model which corrects for elastic and thermal changes;. Ventilation of the 2600 m dome by 16 apertures totalling 50m2;. Insulation of the underside of the concrete dome floor; . Internal air circulation during the day, to reduce heating of the upper telescope steelwork.In 1998 a campaign of K-band image quality (FWHM) measurements showed that after correction for undersampling the median FWHM was 0.433 and 10% of images were indistinguishable from the diffraction limit. Fully sampled images in September 1998 confirmed the correction function; these have FWHM = O."178 (Strehi ratio O.25) and are believed still to be the best ground-based images ever secured without the use of higher-order adaptive optics. Over 21 nights in that month the median FWHM was 0.265. A new secondary mirror has recently been installed and has reduced the RMS wavefront error from -360 nm to -180 nm (in the first instance). A new campaign of image quality measurements has been initiated. The primary mirror cooling system is complete and beginning its operational checkout.