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Discovery Channel Telescope – Technical Information

Technical

The DeVeny Spectrograph

This instrument is the KPNO "White Spectrograph" that had a long career at the 84" telescope on Kitt Peak before being retired. Lowell Observatory obtained it from KPNO on indefinite loan and have modified it to use a CCD detector (along with a number of other changes). It was designed for f/7.5 telescope optics, and is used with a positive lens before focus to speed up the f/17.5 beam from the Perkins telescope to f/7.5.

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The DeVeny spectrograph system includes the f/ratio matching lens, four spectral calibration lamps with computer-controllable power circuits, a slitviewing acquisition camera, the slit/decker mechanisms, another lens to reposition the pupil on the grating, a shutter, various filters, an off-axis parabola collimator, a set of 128x154mm plane reflection gratings, the f/1.25 Wynne camera, and an e2v CCD42-10 CCD (2048x515 13.5 micron pixels, 4 e- RMS, gain 2.1 e-/DN) mounted in a liquid nitrogen cooled dewar. The Wynne camera has two powered reflective surfaces and a series of weak fused silica refractive correction surfaces. The secondary "mirror" (an aluminized, nearly rectangular spot on a key surface) introduces a substantial central obscuration in the camera.

The spectrograph provides low-resolution optical spectra at R500-4000 over 3200 - 1 micron, with a slit length up to 4 arcmin on the Perkins 72 telescope. The grating complement currently includes 1200 g/mm-5000 , 400 g/mm-8500 , 2160 g/mm-5000 , and 300 g/mm-5000 1st-order blazed gratings; other stock rulings are commercially available. The instrument includes pre and post-slit neutral density and order-sorting filters that can be manually placed in the beam. The slit, decker, and the focus of the collimator and camera are also adjusted manually. The grating tilt is motorized, but has not yet been modified to be remotely operable. Halogen lamps and Hg/Ne/Ar/Cd lamps are available for flat fielding and wavelength calibration. The total efficiency of the spectrograph (including telescope optics) is 8-10%.

Although presently in service at our Anderson Mesa site, the DeVeny can be mounted to the DCT RC instrument cube to provide optical spectroscopic capabilities as part of the first light instrument suite.

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TELESCOPE

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Primary Mirror

Secondary Mirror

Active Optics System

Optical Coating System

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Prime focus configuration images

Ritchey-Chretien configuration images

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FIRST LIGHT INSTRUMENTS

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FACILITY

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Building design & construction

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Environment in the dome

SITE

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Site testing

Seeing histogram

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