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Discovery Channel Telescope – Technical Information

Technical

The Large Monolithic Imager (LMI)

The LMI is a highly specialized camera that will serve as the principal imager and workhorse instrument for the first light DCT, with Lowell astronomer Phil Massey as the instrument PI. Fully funded by a grant from the National Science Foundation, the LMI will be built and commissioned in 2010 and early 2011, and will be included as one of the first-light instruments in 2011.

The LMI will employ a 6.1K x 6.1K x 15 μm CCD as its detector, providing a 12.5 arcmin2 FOV and the capability to perform surface brightness studies down to 30 mag/arcsec2. This is a forward-looking approach to wide field imaging with significant advantages over a mosaic. The need for telescope dithers to fill gaps will be eliminated; this will both improve observing efficiency as well as simplify image calibration by eliminating sky brightness changes during successive exposures. Further improvements in calibration are realized by eliminating the need to consider color term differences across multiple CCDs. We will employ a Cryotiger cooling system and control the CCD with a Generation III Leach controller, with which our instrument team has extensive experience.

gr/lmi.jpg

The image at left shows a (non-functional) prototype of the LMI CCD, with a penny shown for scale. The photometric precision attainable with a monolithic CCD is driven at Lowell in part by the need to do deep imaging of extremely faint galaxies as well as studies of the comae and nuclei of comets, but a host of other programs are obviously possible and will be welcomed from scientists with DCT access.

LMI will include two 10-position filter wheels. Each wheel will have an open position plus nine slots for approximately 5x5-inch filters, presently planned to include Johnson UBV plus Kron-Cousins RI, on and off-band Hα, a wideband VR filter, and a set of nine narrowband filters designed for comet imaging and centered on important emission bands between 3090 and 5140 Å as well as nearby continua.

To maximize the field of view, the LMI will be mounted at the straight-through position of the RC instrument cube, as shown in the figure below. Deployable fold mirrors inside the cube will allow fast switching between instruments mounted at the various ports; at present, these include NIHTS and the DeVeny spectrograph. DCT users will therefore be able to conduct programs requiring near-simultaneous imaging and optical/near-IR spectroscopy. Instrument control will be provided through our existing software LOIS (Lowell Observatory Instrument System), currently in use for many of our facilities at Anderson Mesa and elsewhere, running under Linux.

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The DCT will provide a facility guider and wavefront sensor operating upstream of the LMI and its filter wheels. The guide probes will operate in an annulus around the perimeter of the FOV, with sensitivity sufficent to ensure the presence of ~3 suitable guide stars even in areas of the sky with low stellar density.

Besides being the DCT's workhorse, the LMI will set a precedent both for wide-field imaging with monolithic cameras, as well as for more efficient future mosaics.

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TELESCOPE

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Index Logo OPTICS

Primary Mirror

Secondary Mirror

Active Optics System

Optical Coating System

Index Logo MOUNT

Prime focus configuration images

Ritchey-Chretien configuration images

Index Logo CONTROLS

FIRST LIGHT INSTRUMENTS

Index Logo NIHTS

Index Logo LMI

Index Logo The DeVeny Spectrograph

FACILITY

Index Logo OVERVIEW

Building design & construction

Index Logo DOME

Environment in the dome

SITE

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Site testing

Seeing histogram

Index Logo Environmental Assessment (NEPA)

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