LEWIS: a cross-dispersed spectrograph for the 3-um region

Masatoshi Imanishi; Hiroshi Terada; Miwa Goto; Toshinori Maihara

doi:10.1117/12.317333

21 August 1998 LEWIS: a cross-dispersed spectrograph for the 3-μm region

Masatoshi Imanishi, Hiroshi Terada, Miwa Goto, Toshinori Maihara

Proceedings Volume 3354, Infrared Astronomical Instrumentation; (1998) https://doi.org/10.1117/12.317333
Event: Astronomical Telescopes and Instrumentation, 1998, Kona, HI, United States

Abstract

LEWIS is an IR spectrograph designed primarily for spectroscopy in the 3 micrometers region. It is an echelle type spectrograph using a coarse groove grating together with a prism as a cross-disperser. Using LEWIS, we can observe the whole L-band in one exposure with a resolving power over 1250, which makes observations very efficient. A Santa Barbara Research Center 256 X 256 InSb array is employed as a detector. The grating used is characterized by large groove spacing of 125 micrometers and is utilized at very high orders, 25th-37th order in the L-band. A closed-cycle cooler is employed to keep the optics at 90K, and to maintain the detector at 30K. So far, scientific observations have been made at the Steward Observatory 60 inch telescope on Mt. Lemmon, the Steward Observatory 61 inch telescope on Mt. Bigelow, and the Wyoming IR Observatory 88 inch telescope on Mt. Jelm. The achieved throughput of the spectrograph including the quantum efficiency of the detector is about 20 percent. With the present detector control system, observations are background limited at 3.5 micrometers using multiple correlated sampling, and a limiting magnitude of 8.2 mag is achieved for S/N equals 20 in 30 min integration time with 1.5m class telescopes.

Citation Download Citation

Masatoshi Imanishi, Hiroshi Terada, Miwa Goto, and Toshinori Maihara "LEWIS: a cross-dispersed spectrograph for the 3-μm region", Proc. SPIE 3354, Infrared Astronomical Instrumentation, (21 August 1998); https://doi.org/10.1117/12.317333

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