SPIEaug2002_MIKE

SPIEaug2002_MIKE - MIKE: A Double Echelle Spectrograph for...

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MIKE: A Double Echelle Spectrograph for the Magellan Telescopes at Las Campanas Observatory. Rebecca A. Bernstein a,b , Stephen A. Shectman b , Steve Gunnels c , Stefan Mochnacki d , Alex Athey a a Astronomy Department, 830 Dennison Bldg, University of Michigan, Ann Arbor, MI, 48109-1090 b Carnegie Observatories, 813 Santa Barbara St., Pasadena, CA, 91101 c Paragon Engineering, 18231 Old Ranch Road, Tehachapi, CA 93561; d University of Toronto, P.O. Box 360, Richmond Hill, ON L4C 4Y6, Canada Keywords : Spectrograph, echelle ABSTRACT The Magellan Inamori Kyocera Echelle (MIKE) is a double echelle spectrograph designed for use at the Magellan Telescopes at Las Campanas Observatory in Chile. It is currently in the final stages of construction and is scheduled for commissioning in the last quarter of 2002. In standard observing mode, the blue (320-480 nm) and red (440-1000 nm) channels are used simultaneously to obtain spectra over the full wavelength range with only a few gaps in wavelength coverage at the reddest orders. Both channels contain a three-group set of all-spherical, standard optical glass and calcium fluoride lenses which function as both camera and collimator in a double pass configuration. A single, standard echelle grating is used on each side and is illuminated close to true Littrow. Prism cross-dispersers are also used double- pass, and provide a minimum separation between orders of 6 arcsec. Spectral resolution is 19,000 and 25,000 on the red and blue sides, respectively, with a 1 arcsec slit. Typical rms image diameter is less than 0.2 arcsec, so that resolution increases linearly with decreasing slit width. The standard observing mode will use a slit up to 5” long, however a fiber- fed mode will also be available using blocking filters to select the desired orders for up to 256 objects at a time. In this paper, we describe the optical and mechanical design of the instrument. 1. INSTRUMENT OVERVIEW AND DESIGN GOALS General goals for the design of MIKE were to produce a high efficiency, high resolution spectrograph with complete optical wavelength coverage (320nm – 1μm) while minimizing complexity, size, and cost. Given these goals, there are several advantages to the double-beam arrangement. In addition to the obvious efficiency provided by taking two spectra simultaneously, the red/blue wavelength split allows the parallel channels to be optimized for higher throughput and optimal dispersion in several ways. First, we have used prisms rather than gratings for cross-dispersion because of the higher throughput they provide; dual beams allows us to use a highly dispersive prism on the red side, which would be opaque below 400nm. On the blue side, fused silica prisms can be used with negligible losses. Second, the dual– beam configuration allows us to use gratings with different rulings on the red and blue sides, minimizing the variation in the linear free spectral range and optimizing the blaze angle for each side. Finally, the limited red and blue spectral
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SPIEaug2002_MIKE - MIKE: A Double Echelle Spectrograph for...

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