Bruce C. Bigelow

ESI, a New Keck Observatory Echellette Spectrograph and Imager

The Echellette Spectrograph and Imager (ESI) is a multipurpose instrument that has been delivered by the Instrument Development Laboratory of Lick Observatory for use at the Cassegrain focus of the Keck II telescope. ESI saw first light on 1999 August 29. ESI is a multimode instrument that enables the observer to seamlessly switch between three modes during an observation. The three modes of ESI are an R p 13,000 echellette mode, a low-dispersion prismatic mode, and a direct-imaging mode. ESI contains a unique flexure compensation system that reduces the small instrument flexure to negligible proportions. Long-exposure images on the sky show FWHM spot diameters of 34 m m( 0 .34) averaged over the entire field of view. These are the best non-adaptive optics images taken in the visible at Keck Observatory to date. Maximum efficiencies are measured to be 28% for the echellette mode and greater than 41% for low-dispersion prismatic mode including atmospheric, telescope, and detector losses. In this paper, we describe the instrument and its development. We also discuss the performance testing and some observational results.

FIRE: a near-infrared cross-dispersed echellette spectrometer for the Magellan telescopes

FIRE (the Folded-port InfraRed Echellette) is a prism cross-dispersed infrared spectrometer, designed to deliver singleobject R=6000 spectra over the 0.8-2.5 micron range, simultaneously. It will be installed at one of the auxiliary Nasmyth foci of the Magellan 6.5-meter telescopes. FIRE employs a network of ZnSe and Infrasil prisms, coupled with an R1 reflection grating, to image 21 diffraction orders onto a 2048 × 2048, HAWAII-2RG focal plane array. Optionally, a user-controlled turret may be rotated to replace the reflection grating with a mirror, resulting in a singleorder, longslit spectrum with R ~ 1000. A separate, cold infrared sensor will be used for object acquisition and guiding. Both detectors will be controlled by cryogenically mounted SIDECAR ASICs. The availability of low-noise detectors motivates our choice of spectral resolution, which was expressly optimized for Magellan by balancing the scientific demand for increased R with practical limits on exposure times (taking into account statistics on seeing conditions). This contribution describes that analysis, as well as FIREs optical and opto-mechanical design, and the design and implementation of cryogenic mechanisms. Finally, we will discuss our data-flow model, and outline strategies we are putting in place to facilitate data reduction and analysis.

The FIRE infrared spectrometer at Magellan: construction and commissioning

We describe the construction and commissioning of FIRE, a new 0.8-2.5μm echelle spectrometer for the Magellan/ Baade 6.5 meter telescope. FIRE delivers continuous spectra over its full bandpass with nominal spectral resolution R = 6000. Additionally it offers a longslit mode dispersed by the prisms alone, covering the full z to K bands at R ~ 350. FIRE was installed at Magellan in March 2010 and is now performing shared-risk science observations. It is delivering sharp image quality and its throughput is sufficient to allow early observations of high redshift quasars and faint brown dwarfs. This paper outlines several of the new or unique design choices we employed in FIREs construction, as well as early returns from its on-sky performance.

IMACS: the multiobject spectrograph and imager for the Magellan I telescope

The Inamori Magellan Areal Camera and Spectrograph (IMACS) will be one of three first-generation instruments for the Magellan 6.5 m telescopes. It will be installed at the f/11 (Gregorian) Nasmyth focus. This instrument drove the specification and design of the f/11 configuration, which it uses to feed an all-spherical, wide-field collimator. The combination of the Gregorian secondary and refracting collimator lead to 0.2 arc-sec images over a 17 arc-min field with an f/2.66 camera, and 0.4 arc-sec images over a 27 arc- min field with an f/1.49 camera. This paper describes the preliminary specifications for the multiple spectrographic and imaging modes, the optical layout of the instrument and Epps cameras, and strategies for the design and fabrication of the instrument.

SALTICAM:

The Southern African Large Telescope (SALT) is a 10-m class telescope presently under construction at Sutherland in South Africa. It is designed along the lines of the Hobby-Eberly Telescope (HET) at McDonald Observatory in West Texas. SALTICAM will be the Acquisition Camera and simple Science Imager (ACSI) for this telescope. It will also function as the Verification Instrument (VI) to check the performance of the telescope during commissioning. In VI mode, SALTICAM will comprise a filter unit, shutter and cryostat with a 2x1 mosaic of 2k x 4k x 15 micron pixel CCDs. It will be mounted at the f/4.2 corrected prime focus of the telescope. In ACSI mode it will be fed by a folding flat located close to the exit pupil of the telescope. ACSI mode will have the same functional components as VI mode but it will in addition be garnished with focal conversion lenses to re-image the corrected prime focal plane at f/2. The lenses will be made from UV transmitting crystals as the wavelength range for which the instrument is designed will span 320 to 950 nm. In addition to acting as Verification Instrument and Acquisition Camera, SALTICAM will perform simple science imaging in support of other instruments, but will also have a high time resolution capability which is not widely available on large telescopes. This paper will describe the design of the instrument, emphasizing features of particular interest.

0.5M acquisition camera: every big telescope should have one

We describe the Michigan/Magellan Fiber System (M2FS) under construction for use on the Magellan/Clay telescope. M2FS consists of four primary components including: (1) A fiber-fed double spectrograph (MSPec) in which each spectrograph is fed by 128 fibers (for a total multiplexing factor of 256) and each is optimized in to operate from 370- 950 nm; (2) A fiber mounting system (MFib) that supports the fibers and fiber plug plates at the telescope f/11 Nasmyth focal surface and organizes the fibers into ‘shoes’ that are used to place the fibers at the image surface of the MSpec spectrographs;, (3) A new wide-field corrector (WFC) that produces high-quality images over a 30 arcmin diameter field; (4) A unit (MCal) mounted near the telescope secondary that provides wavelength and continuum calibration and that supports a key component in a novel automated fiber identification system. We describe the opto-mechanical properties of M2FS, its modes of operation, and its anticipated performance, as well as potential upgrades including the development of a robotic fiber positioner and an atmospheric dispersion corrector. We describe how the M2FS design could serve as the basis of a powerful wide-field, massively multiplexed spectroscopic survey facility.

M2FS: the Michigan/Magellan Fiber System

The Echellette Spectrograph and Imager (ESI) is one of several second-generation instruments for the Keck telescopes. The motivation for the f/15 Cassegrain-mounted instrument has been to provide a versatile, extremely efficient, and stable system for faint object spectroscopy and imaging, on a comparatively limited schedule and budget. In keeping with these goals, a space-frame instrument structure has been designed, analyzed, and fabricated. The mainframe structure provides the mechanical interface between the telescope and instrument, support points for all the optical, mechanical, and electronic sub-systems, and provides a rigid base for the active- collimator flexure control system. The fundamental concepts and motivation for using a space-frame are discussed, and their application to the design, analysis, and fabrication of the ESI structure is presented.

Determinate space-frame structure for the Keck II echellette spectrograph and imager (ESI)

The finite element analyses of two large lenses for the Keck Telescope High Resolution Echelle Spectrograph are described. The two lenses, one simple lens, and one meniscus, are of fused silica and are approximately 800 mm (30 in.) in diameter. The purpose of the analyses is to determine the deformations of each optic under its own weight, and to identify the simplest, most cost effective mounting cell that will satisfy the optical requirements. Two common radial supports are analyzed, including varieties of hard point and band type mountings. Several types of axial supports are examined including simple three-point mounts, ring mounts, and static deformation mounts. A parametric finite element input routine is described, whereby a solid model and finite element mesh are automatically generated, given the lens diameter, central thickness, and surface radii of curvature. Deformation predictions from the models are compared with theoretical calculations, interferometric testing, and precision profilometry.

Finite element analysis of large lenses for the Keck telescope high-resolution echelle spectrograph

The GMT-Consortium Large Earth Finder (G-CLEF) is an optical-band echelle spectrograph that has been selected as the first light instrument for the Giant Magellan Telescope (GMT). G-CLEF is a general-purpose, high dispersion spectrograph that is fiber fed and capable of extremely precise radial velocity measurements. The G-CLEF Concept Design (CoD) was selected in Spring 2013. Since then, G-CLEF has undergone science requirements and instrument requirements reviews and will be the subject of a preliminary design review (PDR) in March 2015. Since CoD review (CoDR), the overall G-CLEF design has evolved significantly as we have optimized the constituent designs of the major subsystems, i.e. the fiber system, the telescope interface, the calibration system and the spectrograph itself. These modifications have been made to enhance G-CLEF’s capability to address frontier science problems, as well as to respond to the evolution of the GMT itself and developments in the technical landscape. G-CLEF has been designed by applying rigorous systems engineering methodology to flow Level 1 Scientific Objectives to Level 2 Observational Requirements and thence to Level 3 and Level 4. The rigorous systems approach applied to G-CLEF establishes a well defined science requirements framework for the engineering design. By adopting this formalism, we may flexibly update and analyze the capability of G-CLEF to respond to new scientific discoveries as we move toward first light. G-CLEF will exploit numerous technological advances and features of the GMT itself to deliver an efficient, high performance instrument, e.g. exploiting the adaptive optics secondary system to increase both throughput and radial velocity measurement precision.

A preliminary design for the GMT-Consortium Large Earth Finder (G-CLEF)

The Inamori-Magellan Areal Camera and Spectrograph (IMACS) features a 8K x 8K, 6.7 Megapixel detector system, which is mounted in a cryogenic vacuum vessel with a combination of features that are unique among the current generation of astronomical multi-detector array systems. Closed-cycle coolers, commercial stages for flexure compensation, flexure control detectors, array focus control, composite thermal isolation truss and other features are described.