We describe the camera articulation prototype (CAP) for the Giant Magellan Telescope Multi-object Astronomical and Cosmological Spectrograph (GMACS), which is a wide field, multi-object, moderate-resolution, optical spectrograph of the Giant Magellan Telescope (GMT). The GMACS will have the Camera and Grating Articulation System (CGAS) which has two independent cameras and grating modules. The grating angles and the camera angles can be changed to adjust the dispersed light bands on the detector. The electronics components of this system include motors with encoder, pneumatic brakes, and limit switches. We demonstrate how to control the camera angles using a prototype that is designed for the camera articulation controller as a miniature model of the GMACS. The prototype was built with commercially-available extruded aluminum struts and 3D-printed parts and includes two motors with encoders. The prototype was produced quickly and inexpensively, but replicates all functions of the camera articulation mechanism in GMACS. We have developed the control package for the prototype that will be one of the GMACS Device Control System (DCS). The software is designed by the Agile development process and SysML, and developed using Visual C++ on Windows OS. This software has five major control functions: power, homing, resolution mode changing, limit detection, and emergency process. The limit detection is implemented by setting up the limit angle range in the software, because the limit switches are not included in the prototype. We present the demonstration result and discuss the details of the communication route about data flow between high-end user software and hardware components.
We describe and present initial testing of TCal, a mobile spectrophotometric calibration system that will be used to characterize the throughput as a function of wavelength for imaging systems at observatories around the world. TCal measurements will enhance the science return from follow-up observations of imaging surveys such as LSST (Large Synoptic Survey Telescope) and DES (Dark Energy Survey) by placing all tested imaging systems on a common photometric baseline. TCal uses a ~ 1 nm bandpass tunable light source to measure the instrumental response function of imaging systems from 300 nm to 1100 nm, including the telescope, optics, filters, windows, and detector. The system is comprised of a monochromator-based light source illuminating a dome flat field screen monitored by a calibrated CCD, which allows determination of the telescope throughput as a function of wavelength. This calibration will be performed at 1-8m telescopes that expect to devote time towards survey follow-up. Performing the calibration on these telescopes will reduce systematic errors due to small differences in bandpass, making follow-up efforts more precise and accurate.
The Giant Magellan Telescope Multi-object Astronomical and Cosmological Spectrograph (GMACS) is a first light instrument for the Giant Magellan Telescope (GMT). It will provide multi-object spectroscopy in wide wavelength coverage and wide field of view. The scientific objectives include exoplanet atmospheres, star formation and chemical evolution studies, galaxy assembly histories, and intergalactic medium tomography. The optical layouts are optimized to have high throughput in the natural seeing limit. In this presentation, we report the current status of the instrument development.
We describe the current electronics prototypes for the Flexure Compensation System (FCS) and the Slit Mask Exchange Mechanism (SMEM) for GMACS, a wide-field, multi-object, moderate-resolution optical spectrograph for the Giant Magellan Telescope (GMT). We discuss the details of the FCS and SMEM prototypes, how the prototypes relate to the preliminary conceptual designs of these systems, and what information the prototypes give that can be applied to the final design, as well as the possible next steps for each prototype.
MANIFEST is a multi-object fibre facility for the Giant Magellan Telescope that uses ‘Starbug’ robots to accurately position fibre units across the telescope’s focal plane. MANIFEST, when coupled to the telescope’s planned seeinglimited instruments, offers access to larger fields of view; higher multiplex gains; versatile focal plane reformatting of the focal plane via integral-field-units; image-slicers; and in some cases higher spatial and spectral resolution. The TAIPAN instrument on the UK Schmidt Telescope is now close to science verification which will demonstrate the feasibility of the Starbug concept. We are now moving into the conceptual development phase for MANIFEST, with a focus on developing interfaces for the telescope and for the instruments.
We describe the optical design of GMACS, a multi-object wide field optical spectrograph currently being developed for the Giant Magellan Telescope (GMT). Optical spectrographs for the emerging generation of Extreme Large Telescopes (ELTs) have unique design issues. For example, the combination of both the largest field of view practical and beam widths achieving the desired spectral resolutions force the design of seeing limited ELT optical spectrographs to include large refractive elements, which in turn requires a compromise between the optical performance, manufacturability, and operability. We outline the details of the GMACS optical design subsystems, their individual and combined optical performance, and the preliminary flexure tolerances. Updates to the detector specifications, field acquisition/alignment optics, and optical considerations for active flexure control are also discussed. The resulting design meets the technical instrument requirements generated from the GMACS science requirements, is expected to satisfy the available project budget, and has an acceptable level of risk for the subsystem manufacture and assembly.
We report on an expanded catalog of total and specular reflectance measurements of various common (and uncommon) materials used in the construction and/or baffling of optical systems. Total reflectance is measured over a broad wavelength range (250 nm < λ < 2500 nm) that is applicable to ultraviolet, visible, and near-infrared instrumentation. Characterization of each sample's specular reflection was measured using a helium-neon laser in two degree steps from near normal to grazing angles of incidence. The total and specular reflection measurements were then used to derive the specular fraction of each material.
An important tool for the development of the next generation of extremely large telescopes (ELTs) is a robust Systems Engineering (SE) methodology. GMACS is a first-generation multi-object spectrograph that will work at visible wavelengths on the Giant Magellan Telescope (GMT). In this paper, we discuss the application of SE to the design of next-generation instruments for ground-based astronomy and present the ongoing development of SE products for the GMACS spectrograph, currently in its Conceptual Design phase. SE provides the means to assist in the management of complex projects, and in the case of GMACS, to ensure its operational success, maximizing the scientific potential of GMT.
The goal of this project was to build a device capable of measuring both the specular reflectivity of black materials, as well as the Lambertian reflectivity of white materials over their full range of incident and observed angles, respectively. The MADLaSR (Multi-Angle Detection of Lambertian and Specular Reflectivity) is a device designed for specular reflectivity testing in the range of 10° < θ < 160° and for Lambertian reflectivity testing in the range of 10° < θ < 85°. The data collected from this device may be used to influence the design of optical systems, aerospace structures, or other devices in which maximum light control is a necessary consideration. This paper will discuss the design and functionality of the MADLaSR.
The Visible Integral-field Replicable Unit Spectrograph (VIRUS) consists of 156 identical spectrographs fed by 35,000 fibers from the upgraded 10-meter Hobby-Eberly Telescope (HET). VIRUS is in a phased deployment. At the submission of this paper, over half of the units are installed and the full support infrastructure is operational. This paper will describe the VIRUS infrastructure which includes the physical support system, the air cooling, the cryogenic cooling, and the temperature control of VIRUS. The paper will also discuss the various installation, maintenance, and operational procedures based on growing experience with the VIRUS array.
H. T. Diehl, E. Neilsen, R. Gruendl, T. M. Abbott, S. Allam, O. Alvarez, J. Annis, E. Balbinot, S. Bhargava, K. Bechtol, G. Bernstein, R. Bhatawdekar, S. Bocquet, D. Brout, R. Capasso, R. Cawthon, C. Chang, E. Cook, C. Conselice, J. Cruz, C. D'Andrea, L. da Costa, R. Das, D. DePoy, A. Drlica-Wagner, A. Elliott, S. Everett, J. Frieman, A. Fausti Neto, A. Ferté, I. Friswell, K. Furnell, L. Gelman, D. Gerdes, M. S. Gill, D. Goldstein, D. Gruen, D. Gulledge, S. Hamilton, D. Hollowood, K. Honscheid, D. James, M. Johnson, M. W. Johnson, S. Kent, R. Kessler, G. Khullar, E. Kovacs, A. Kremin, R. Kron, N. Kuropatkin, J. Lasker, A. Lathrop, T. Li, M. Manera, M. March, J. Marshall, M. Medford, F. Menanteau, I. Mohammed, M. Monroy, B. Moraes, E. Morganson, J. Muir, M. Murphy, B. Nord, A. Pace, A. Palmese, Y. Park, F. Paz-Chinchón, M. E. Pereira, D. Petravick, A. Plazas, J. Poh, T. Prochaska, A. Romer, K. Reil, A. Roodman, M. Sako, M. Sauseda, D. Scolnic, L. Secco, I. Sevilla-Noarbe, N. Shipp, J. Smith, M Soares-Santos, B. Soergel, A. Stebbins, K. Story, K. Stringer, F. Tarsitano, B. Thomas, D. Tucker, K. Vivas, A. Walker, M.-Y. Wang, C. Weaverdyck, N. Weaverdyck, W. Wester, C. Wethers, R. Wilkenson, H.-Y Wu, B. Yanny, A. Zenteno, Y. Zhang
The Dark Energy Survey (DES) is an operating optical survey aimed at understanding the accelerating expansion of the universe using four complementary methods: weak gravitational lensing, galaxy cluster counts, baryon acoustic oscillations, and Type Ia supernovae. To perform the 5000 sq-degree wide field and 30 sq-degree supernova surveys, the DES Collaboration built the Dark Energy Camera (DECam), a 3 square-degree, 570-Megapixel CCD camera that was installed at the prime focus of the Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory (CTIO). DES has completed its third observing season out of a nominal five. This paper describes DES “Year 4” (Y4) and “Year 5” (Y5), the survey strategy, an outline of the survey operations procedures, the efficiency of operations and the causes of lost observing time. It provides details about the quality of these two-season's data, a summary of the overall status, and plans for the final survey season.
We present total reflectance measurements and Lambertian characterization of various materials that are commonly (and uncommonly) used as a screen for imaging system calibration (such as flat fielding). We measure the total reflectance of the samples over a broad wavelength range (250 nm < λ < 2500 nm) that is of interest to astronomical instruments in the ultraviolet, visible, and near-infrared regimes. A Helium-Neon laser was used to determine how closely the various materials' diffuse reflectance characteristics match that of a Lambertian surface.
We describe the latest optomechanical design of GMACS, a wide-field, multi-object, moderate-resolution optical spectrograph for the Giant Magellan Telescope (GMT). Specifically, we discuss the details of the structure, mechanisms, optical mounts and deflection tracking/compensation as well as the requirements and considerations used to guide the design. We also discuss GMACS’s interfaces with GMT and other instruments.
We discuss the latest developments of a spectrograph for the Giant Magellan Telescope. The instrument is designed to provide high throughput, moderate resolution, optical spectra for the telescope and be capable of flexible and rapid reconfiguration. The focal plane can be populated with custom slit masks or multiple fibers, allowing for observations of multiple objects simultaneously.
The Visible Integral-field Replicable Unit Spectrograph (VIRUS) consists of 156 identical spectrographs (arrayed as 78 pairs, each with a pair of spectrographs) fed by 35,000 fibers, each 1.5 arcsec diameter, at the focus of the upgraded 10 m Hobby-Eberly Telescope (HET). VIRUS has a fixed bandpass of 350-550 nm and resolving power R~750. The fibers are grouped into 78 integral field units, each with 448 fibers and 20 m average length. VIRUS is the first example of large-scale replication applied to optical astronomy and is capable of surveying large areas of sky, spectrally. The VIRUS concept offers significant savings of engineering effort and cost when compared to traditional instruments. The main motivator for VIRUS is to map the evolution of dark energy for the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX), using 0.8M Lyman-alpha emitting galaxies as tracers. The VIRUS array has been undergoing staged deployment starting in late 2015. Currently, more than half of the array has been populated and the HETDEX survey started in 2017 December. It will provide a powerful new facility instrument for the HET, well suited to the survey niche of the telescope, and will open up large spectroscopic surveys of the emission line universe for the first time. We will review the current state of production, lessons learned in sustaining volume production, characterization, deployment, and commissioning of this massive instrument.
We describe TCal, a mobile spectrophotometric calibration system that will be used to characterize the throughput as a function of wavelength of imaging systems at observatories around the world. TCal measurements will enhance the science return from follow-up observations of imaging surveys such as LSST (Large Synoptic Survey Telescope) and DES (Dark Energy Survey) by placing all tested imaging systems on a common photometric baseline. TCal uses a 1 nm bandpass tunable light source to measure the instrumental response function of imaging systems from 300 nm to 1100 nm, including the telescope, optics, filters, windows, and the detector. The system is comprised of a monochromator-based light source illuminating a dome flat field screen monitored by calibrated photodiodes, which allows determination of the telescope throughput as a function of wavelength. This calibration will be performed at 1-8m telescopes that expect to devote time towards survey follow-up. Performing the calibration on these telescopes will reduce systematic errors due to small differences in bandpass, making follow-up efforts more precise and accurate.
We present the current optical design of GMACS, a multi-object wide field optical spectrograph currently being developed for the Giant Magellan Telescope, a member of the emerging generation of Extremely Large Telescopes (ELTs). Optical spectrographs for ELTs have unique design challenges and issues. For example, the combination of the largest practical field of view and beam widths necessary to achieve the desired spectral resolutions force the design of seeing limited ELT optical spectrographs to include aspheric lenses, broadband dichroics, and volume phase holographic gratings - all necessarily very large. We here outline details of the collimator and camera subsystems, the design methodology and trade-off analyses used to develop the collimator subsystem, the individual and combined subsystem performances and the predicted tolerances.
MANIFEST is a facility multi-object fibre system for the Giant Magellan Telescope, which uses ‘Starbug’ fibre positioning robots. MANIFEST, when coupled to the telescope’s planned seeing-limited instruments, GMACS, and G-CLEF, offers access to: larger fields of view; higher multiplex gains; versatile reformatting of the focal plane via IFUs; image-slicers; and in some cases higher spatial and spectral resolution. The Prototyping Design Study phase for MANIFEST, nearing completion, has focused on developing a working prototype of a Starbugs system, called TAIPAN, for the UK Schmidt Telescope, which will conduct a stellar and galaxy survey of the Southern sky. The Prototyping Design Study has also included work on the GMT instrument interfaces. In this paper, we outline the instrument design features of TAIPAN, highlight the modifications that will be necessary for the MANIFEST implementation, and provide an update on the MANIFEST/instrument interfaces.
The Visible Integral-field Replicable Unit Spectrograph (VIRUS) consists of 156 identical spectrographs (arrayed as 78 pairs) fed by 35,000 fibers, each 1.5 arcsec diameter, at the focus of the upgraded 10 m Hobby-Eberly Telescope (HET). VIRUS has a fixed bandpass of 350-550 nm and resolving power R~700. VIRUS is the first example of industrial-scale replication applied to optical astronomy and is capable of surveying large areas of sky, spectrally. The VIRUS concept offers significant savings of engineering effort, cost, and schedule when compared to traditional instruments. The main motivator for VIRUS is to map the evolution of dark energy for the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX‡), using 0.8M Lyman-alpha emitting galaxies as tracers. The VIRUS array is undergoing staged deployment during 2016 and 2017. It will provide a powerful new facility instrument for the HET, well suited to the survey niche of the telescope, and will open up large spectroscopic surveys of the emission line universe for the first time. We will review the production, lessons learned in reaching volume production, characterization, and first deployment of this massive instrument.
We describe a preliminary conceptual optomechanical design for GMACS, a wide-field, multi-object, moderate resolution optical spectrograph for the Giant Magellan Telescope (GMT). This paper describes the details of the GMACS optomechanical conceptual design, including the requirements and considerations leading to the design, mechanisms, optical mounts, and predicted flexure performance.
We present a preliminary conceptual optical design for GMACS, a wide field, multi-object, optical spectrograph currently being developed for the Giant Magellan Telescope (GMT). We include details of the optical design requirements derived from the instrument scientific and technical objectives and demonstrate how these requirements are met by the current design. Detector specifications, field acquisition/alignment optics, and optical considerations for the active flexure control system are also discussed.
VIRUS is a massively replicated spectrograph built for HETDEX, the Hobby Eberly Telescope Dark Energy Experiment. It consists of 156 channels within 78 units fed by 34944 fibers over the 22 arcminute field of the upgraded HET. VIRUS covers a relatively narrow bandpass (350-550nm) at low resolution (R ~ 700) to target the emission of Lyman-alpha emitters (LAEs) for HETDEX. VIRUS is a first demonstration of industrial style assembly line replication in optical astronomy. Installation and testing of VIRUS units began in November of 2015. This winter we celebrated the first on sky instrument activity of the upgraded HET, using a VIRUS unit and LRS2-R (the upgraded facility Low Resolution Spectrograph for the HET). Here we describe progress in VIRUS installation and commissioning through June 2016. We include early sky data obtained to characterize spectrograph performance and on sky performance of the newly upgraded HET. As part of the instrumentation for first science light at the HET, the IFU fed spectrographs were used to test a full range of telescope system functionality including the field calibration unit (FCU).We also use placement of strategic IFUs to map the new HET field to the fiber placement, and demonstrate actuation of the dithering mechanism key to HETDEX observations.
The Hobby-Eberly Telescope (HET) is an innovative large telescope, located in West Texas at the McDonald Observatory. The HET operates with a fixed segmented primary and has a tracker, which moves the four-mirror corrector and prime focus instrument package to track the sidereal and non-sidereal motions of objects. We have completed a major multi-year upgrade of the HET that has substantially increased the pupil size to 10 meters and the field of view to 22 arcminutes by replacing the corrector, tracker, and prime focus instrument package. The new wide field HET will feed the revolutionary integral field spectrograph called VIRUS, in support of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX§), a new low resolution spectrograph (LRS2), an upgraded high resolution spectrograph (HRS2), and later the Habitable Zone Planet Finder (HPF). The upgrade is being commissioned and this paper discusses the completion of the installation, the commissioning process and the performance of the new HET.
The Visible Integral-field Replicable Unit Spectrograph (VIRUS) is a baseline array of 150 copies of a simple, fiber-fed integral field spectrograph that will be deployed on the Hobby-Eberly Telescope (HET). VIRUS is the first optical astronomical instrument to be replicated on an industrial scale, and represents a relatively inexpensive solution for carrying out large-area spectroscopic surveys, such as the HET Dark Energy Experiment (HETDEX). Each spectrograph contains a volume phase holographic (VPH) grating with a 138 mm diameter clear aperture as its dispersing element. The instrument utilizes the grating in first-order for 350 < λ (nm) < 550. Including witness samples, a suite of 170 VPH gratings has been mass produced for VIRUS. Here, we present the design of the VIRUS VPH gratings and a discussion of their mass production. We additionally present the design and functionality of a custom apparatus that has been used to rapidly test the first-order diffraction efficiency of the gratings for various discrete wavelengths within the VIRUS spectral range. This device has been used to perform both in-situ tests to monitor the effects of adjustments to the production prescription as well as to carry out the final acceptance tests of the gratings' diffraction efficiency. Finally, we present the as-built performance results
for the entire suite of VPH gratings.
The Visible Integral-Field Replicable Unit Spectrograph (VIRUS) instrument will be installed at the Hobby-Eberly
Telescope† in the near future. The instrument will be housed in two enclosures that are mounted adjacent to the
telescope, via the VIRUS Support Structure (VSS). We have designed the enclosures to support and protect the
instrument, to enable servicing of the instrument, and to cool the instrument appropriately while not adversely affecting
the dome environment. The system uses simple HVAC air handling techniques in conjunction with thermoelectric and
standard glycol heat exchangers to provide efficient heat removal. The enclosures also provide power and data transfer
to and from each VIRUS unit, liquid nitrogen cooling to the detectors, and environmental monitoring of the instrument
and dome environments. In this paper, we describe the design and fabrication of the VIRUS enclosures and their subsystems.
We review a conceptual design for a moderate resolution optical spectrograph for the Giant Magellan Telescope (GMT).
The spectrograph is designed to make use of the large field-of-view of the GMT and be suitable for observations of very
faint objects across a wide range of wavelengths. We also review the status of the instrument and on-going trade studies
designed to update the instrument science objectives and technical requirements.
The Hobby-Eberly Telescope (HET) is an innovative large telescope located in West Texas at the McDonald Observatory. The HET operates with a fixed segmented primary and has a tracker, which moves the four-mirror optical corrector and prime focus instrument package to track the sidereal and non-sidereal motions of objects. A major upgrade of the HET is in progress that will substantially increase the pupil size to 10 meters (from 9.2 m) and the field of view to 22 arcminutes (from 4 arcminutes) by replacing the corrector, tracker, and prime focus instrument package. In addition to supporting existing instruments, and a new low resolution spectrograph, this wide field upgrade will feed a revolutionary new integral field spectrograph called VIRUS, in support of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX§). The upgrade is being installed and this paper discusses the current status.
VIRUS is the massively replicated fiber-fed spectrograph being built for the Hobby-Eberly Telescope to support
HETDEX (the Hobby-Eberly Telescope Dark Energy Experiment). The instrument consists of 156 identical
channels, fed by 34,944 fibers contained in 78 integral field units, deployed in the 22 arcminute field of the
upgraded HET. VIRUS covers 350-550nm at R ≈ 700 and is built to target Lyman α emitters at 1.9 < z < 3.5 to
measure the evolution of dark energy. Here we present the assembly line construction of the VIRUS spectrographs,
including their alignment and plans for characterization. We briefly discuss plans for installation on the telescope.
The spectrographs are being installed on the HET in several stages, and the instrument is due for completion
by the end of 2014.
The Visible Integral-field Replicable Unit Spectrograph (VIRUS) consists of a baseline build of 150 identical
spectrographs (arrayed as 75 unit pairs) fed by 33,600 fibers, each 1.5 arcsec diameter, at the focus of the upgraded 10
m Hobby-Eberly Telescope (HET). VIRUS has a fixed bandpass of 350-550 nm and resolving power R~700. VIRUS is
the first example of industrial-scale replication applied to optical astronomy and is capable of surveying large areas of
sky, spectrally. The VIRUS concept offers significant savings of engineering effort, cost, and schedule when compared
to traditional instruments.
The main motivator for VIRUS is to map the evolution of dark energy for the Hobby-Eberly Telescope Dark Energy
Experiment (HETDEX), using 0.8M Lyman-α emitting galaxies as tracers. The full VIRUS array is due to be deployed starting at the end of 2014 and will provide a powerful new facility instrument for the HET, well suited to the
survey niche of the telescope, and will open up large area surveys of the emission line universe for the first time.
VIRUS is in full production, and we are about half way through. We review the production design, lessons learned in
reaching volume production, and preparation for deployment of this massive instrument. We also discuss the application
of the replicated spectrograph concept to next generation instrumentation on ELTs.
We present total and specular reflectance measurements of various materials that are commonly (and uncommonly) used
to provide baffling and/or to minimize the effect of stray light in optical systems. More specifically, we investigate the
advantage of using certain black surfaces and their role in suppressing stray light on detectors in optical systems. We
measure the total reflectance of the samples over a broad wavelength range (250 < λ < 2500 nm) that is of interest to
astronomical instruments in the ultraviolet, visible, and near-infrared regimes. Additionally, we use a helium-neon laser
to measure the specular reflectance of the samples at various angles. Finally, we compare these two measurements and
derive the specular fraction for each sample.
Jennifer Marshall, Darren DePoy, Travis Prochaska, Richard Allen, Patrick Williams, Jean-Philippe Rheault, Ting Li, Daniel Nagasawa, Christopher Akers, David Baker, Emily Boster, Caitlin Campbell, Erika Cook, Alison Elder, Alex Gary, Joseph Glover, Michael James, Emily Martin, Will Meador, Nicholas Mondrik, Marisela Rodriguez-Patino, Steven Villanueva, Gary Hill, Sarah Tuttle, Brian Vattiat, Hanshin Lee, Taylor Chonis, Gavin Dalton, Mike Tacon
The Visual Integral-Field Replicable Unit Spectrograph (VIRUS) instrument is a baseline array 150 identical fiber fed
optical spectrographs designed to support observations for the Hobby-Eberly Telescope Dark Energy Experiment
(HETDEX). The collimator subassemblies of the instrument have been assembled in a production line and are now
complete. Here we review the design choices and assembly practices used to produce a suite of identical low-cost
spectrographs in a timely fashion using primarily unskilled labor.
Traditional color and airmass corrections can typically achieve ~0.02 mag precision in photometric observing conditions.
A major limiting factor is the variability in atmospheric throughput, which changes on timescales of less than a night.
We present preliminary results for a system to monitor the throughput of the atmosphere, which should enable
photometric precision when coupled to more traditional techniques of less than 1% in photometric conditions. The
system, aTmCam, consists of a set of imagers each with a narrow-band filter that monitors the brightness of suitable
standard stars. Each narrowband filter is selected to monitor a different wavelength region of the atmospheric
transmission, including regions dominated by the precipitable water, aerosol optical depth, etc. We have built a
prototype system to test the notion that an atmospheric model derived from a few color indices measurements can be an
accurate representation of the true atmospheric transmission. We have measured the atmospheric transmission with both
narrowband photometric measurements and spectroscopic measurements; we show that the narrowband imaging
approach can predict the changes in the throughput of the atmosphere to better than ~10% across a broad wavelength
range, so as to achieve photometric precision less than 0.01 mag.
We describe the mechanical assembly and optical alignment processes used to construct the Visual Integral-Field
Replicable Unit Spectrograph (VIRUS) instrument. VIRUS is a set of 150+ optical spectrographs designed to support
observations for the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). To meet the instrument's
manufacturing constraints, a production line will be set up to build subassemblies in parallel. To aid in the instrument's
assembly and alignment, specialized fixtures and adjustment apparatuses have been developed. We describe the design
and operations of the various optics alignment apparatuses, as well as the mirrors' alignment and bonding fixtures.
The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) uses a novel technique of replicated spectrographs (VIRUS) to measure dark energy at intermediate redshifts (2 < z < 4). VIRUS contains over 30,000 fibers and over 160 independent and identical channels. Here we report on the construction and characterization of the initial batch of VIRUS spectrograph cameras. Assembly of the first batch of 16 is in progress. A brief overview of the assembly is presented, and where available performance is compared to specification.
The Visible Integral-field Replicable Unit Spectrograph (VIRUS) consists of a baseline build of 150 identical
spectrographs (arrayed as 75 units, each with a pair of spectrographs) fed by 33,600 fibers, each 1.5 arcsec diameter,
deployed over the 22 arcminute field of the upgraded 10 m Hobby-Eberly Telescope (HET). The goal is to deploy 82
units. VIRUS has a fixed bandpass of 350-550 nm and resolving power R~700. VIRUS is the first example of
industrial-scale replication applied to optical astronomy and is capable of spectral surveys of large areas of sky. This
approach, in which a relatively simple, inexpensive, unit spectrograph is copied in large numbers, offers significant
savings of engineering effort, cost, and schedule when compared to traditional instruments.
The main motivator for VIRUS is to map the evolution of dark energy for the Hobby-Eberly Telescope Dark Energy
Experiment (HETDEX) using 0.8M Lyman-α emitting galaxies as tracers. The full VIRUS array is due to be deployed
by early 2014 and will provide a powerful new facility instrument for the HET, well suited to the survey niche of the
telescope. VIRUS and HET will open up wide-field surveys of the emission-line universe for the first time. We present
the production design and current status of VIRUS.
We describe a spectrophotometric calibration system that is being implemented as part of the DES DECam project at the
Blanco 4 meter at CTIO. Our calibration system uses a 1nm wide tunable source to measure the instrumental response
function of the telescope optics and detector from 300nm up to 1100nm. This calibration will be performed regularly to
monitor any change in the transmission function of the telescope during the 5 year survey. The system consists of a
monochromator based tunable light source that provides illumination on a dome flat that is monitored by calibrated
photodiodes that allow us to measure the telescope throughput as a function of wavelength. Our system has a peak
output power of 2 mW, equivalent to a flux of approximately 800 photons/s/pixel on DECam.
We describe the conceptual optomechanical design for GMACS, a wide-field, multi-object, moderate-resolution optical
spectrograph for the Giant Magellan Telescope (GMT). GMACS is a candidate first-light instrument for the GMT and
will be one of several instruments housed in the Gregorian Instrument Rotator (GIR) located at the Gregorian focus. The
instrument samples a 9 arcminute x 18 arcminute field of view providing two resolution modes (i.e, low resolution, R ~
2000, and moderate resolution, R ~ 4000) over a 3700 Å to 10200 Å wavelength range. To minimize the size of the
optics, four fold mirrors at the GMT focal plane redirect the full field into four individual "arms", that each comprises a
double spectrograph with a red and blue channel. Hence, each arm samples a 4.5 arcminute x 9 arcminute field of view.
The optical layout naturally leads to three separate optomechanical assemblies: a focal plane assembly, and two identical
optics modules. The focal plane assembly contains the last element of the telescope's wide-field corrector, slit-mask,
tent-mirror assembly, and slit-mask magazine. Each of the two optics modules supports two of the four instrument arms
and houses the aft-optics (i.e. collimators, dichroics, gratings, and cameras). A grating exchange mechanism, and
articulated gratings and cameras facilitate multiple resolution modes. In this paper we describe the details of the
GMACS optomechanical design, including the requirements and considerations leading to the design, mechanism
details, optics mounts, and predicted flexure performance.
We present a conceptual design for a moderate resolution optical spectrograph for the Giant Magellan Telescope (GMT).
The spectrograph is designed to make use of the large field-of-view of the GMT and be suitable for observations of very
faint objects across a wide range of optical wavelengths. We show some details of the optical and mechanical design of
the instrument.
The Visible Integral-Field Replicable Unit Spectrograph (VIRUS) is an integral field spectrograph to support
observations for the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). The VIRUS instrument is fed by
more than 33,000 optical fibers and consists of 150 spectrographs in 75 individual, identical units. This paper discusses
the evolution in mechanical design of the VIRUS unit spectrographs to maximize the cost benefit from volume
production. Design features which enable volume manufacture and assembly are discussed. Strategies for reducing
part count while enabling precision alignment are detailed. Design considerations for deployment, operation, and
maintenance en mass at the Hobby-Eberly Telescope are also made. In addition, several enabling technologies are
described including the use of cast aluminum in vacuum housings, use of cast Invar, and processing cast parts for
precision tolerances.
The Visible Integral-Field Replicable Unit Spectrograph (VIRUS) Instrument is a set of 150+ optical spectrographs to
support observations for the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). We plan to use a
production line assembly process to construct the large number of VIRUS units. This allows each sub-assembly of a
VIRUS unit to be interchangeable amongst all other VIRUS units. A production line manufacturing procedure will
enable various sub-assemblies to be built and tested in parallel. Examples of alignment and assembly fixtures required
for the VIRUS manufacturing process include a camera mirror alignment system, a collimator structure assembly device,
a collimator mirror mounting tool, and a grating alignment system. In this paper we describe the design of these fixtures
and their importance in the VIRUS assembly process.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.