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IR Instrumentation Program News: Getting Ready for AO (1Dec95) (from CTIO, NOAO Newsletter No. 44, December 1995) f/14 Tip-Tilt Secondary The f/14 tip-tilt project, presently well advanced, will bring the benefits of low order adaptive optics to the Blanco 4-m in second semester 1996. With tip-tilt we expect to produce images in the K (2.2 um) band with core FWHM of a few tenths of an arcsecond. This f-ratio will also allow CTIO to exchange IR instrumentation with the Gemini 8-m telescope and KPNO. Capital costs have been kept down by "recycling" an existing, unfinished mirror and a complete mechanical assembly, left over from the original construction of the telescope. These were originally intended for an f/13 Cass focus, which was never implemented. A dummy mirror with the same moment of inertia and mass as the secondary mirror was successfully installed in the mirror cell and shaken in the La Serena machine shop with a full amplitude throw of 15 mm (3"). At frequencies up to 80 Hz the dummy responded very well to the drive signal. The mirror itself has been trimmed and cored for lightweighting, and is currently being figured in the NOAO optical shop in Tucson. It will be installed in the telescope in late February 1996. It will initially provide a passive f/14 focus. We plan to begin testing the tip-tilt capability of the secondary following the extended winter down time of the Blanco 4-m (described in another article in this Newsletter). COB Goes South Both infrared imaging and spectroscopy will benefit tremendously from the improvement in image quality offered by the f/14 tip-tilt secondary. A plan is in place to upgrade the detector in the Cryogenic Optical Bench (COB) and transfer it from KPNO to CTIO to take advantage of the tip-tilt capability of the Blanco 4-m for imaging. COB will be fitted with an Aladdin array between June and September 1996 and will be brought to Chile in October 1996. With its Aladdin array in place COB will offer 0.1" pixels which should be well matched to tip-tilt images obtained in good seeing on the Blanco 4-m. COB will serve both as the facitility imager for the 4-m and as the first light imager for the Southern Gemini 8-m telescope. The IRS Goes f/14 The CTIO IR spectrograph "IRS," as currently configured, is optically matched to an f/30 input beam and so requires modification to work with the new f/14 secondary. As an instrument improvement project just approved by ACTR, the IRS will be optically upgraded to accept an f/14 beam, to provide the narrower slits matched to the expected tight image cores at K, and to provide an improved cold stop, which should help instrumental performance in the thermal infrared. While the design and fabrication can proceed with the instrument in active service, the final modification of the dewar will require the IRS to be removed from use for two months. This is tentatively scheduled for January-February 1997, subject to change as the project schedule is finalized. This will affect instrument availability for the second semester 1996 so check the March NOAO Newsletter before submitting proposals. Richard Elston, Brooke Gregory
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