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Discovery Channel Telescope – Technical Information

Technical

Near Infrared High Throughput Spectrograph (NIHTS)

This is a low-resolution spectrograph funded by NASA's Planetary Astronomy and Planetary Major Equipment programs with Lowell astronomer Henry Roe as the PI. It will be built and commissioned in 2010 and early 2011, and will be included as one of the first-light instruments in 2011.

NIHTS will be mounted on the RC instrument cube, allowing for fast switching between its capabilities and those of the other RC instruments using a deployable fold mirror. Operationally this fold mirror will be a dichroic, reflecting infrared light to NIHTS and allowing visible light to pass through to the Large Monolithic Imager (LMI) at the bottom of the instrument cube. This enables simultaneous near-infrared spectroscopy and visible imaging of targets. NIHTS will cover 0.9-2.4 μm at resolution of roughly 100, though a variety of resolutions will be selectable via a slit plate with 2, 3, 4, and 12-pixel-wide slits. The widest slit will operate NIHTS in SED mode, allowing for accurate flux calibration, while the 3 and 4-pixel slits are closely matched to typical seeing at the DCT site (0.86" mean). Different resolutions will be rapidly selectable by dithering the telescope, and a typical observation is anticipated to involve a sequence of dithers both at the desired resolution and at SED resolution for calibration purposes. Flat field and wavelength calibration will use a screen mounted inside the DCT dome.

The figure below shows the position of NIHTS as mounted on the DCT RC instrument cube. It is physically small, thermally isolated inside a vacuum dewar, and will be kept cold by a Stirling cycle cooler. Below the instrument diagram is the originally proposed optical layout, which has now evolved to include an Offner Relay to provide a cold stop.

gr/nihts-schematic.jpg

NIHTS will include an InGaAs slit-viewing camera for target acquisition. (The DCT will also provide a facility guider and wavefront sensor for offset guiding during exposures on targets too faint to guide on directly.) The instrument employs a gold-coated fold mirror, and utilizes a double pass through a prism to keep the instrument compact. NIHTS was originally designed for a 256x256 PICNIC detector, but we have now secured a high-QE 1024x1024 HAWAII-1 to serve as the primary science detector. This upgrade in planned detector led to a redesign of the optical path to better take advantage of the larger array.

While the initial top priority for NIHTS will be to carry out PI Roe's Kuiper Belt survey, it will also be available to other investigators with access to DCT.

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TELESCOPE

Index Logo SPECIFICATIONS

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

Index Logo OVERVIEW

Site testing

Seeing histogram

Index Logo Environmental Assessment (NEPA)

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