KEYWORDS: Spectrographs, Control software, Software development, Charge-coupled devices, Camera shutters, Design and modelling, Control systems, Computer architecture, Data acquisition, Switches
Local Volume Mapper Spectrograph Control Package (LVMSCP) is the software that controls three spectrographs to acquire science spectral data cubes automatically. The software architecture design based on Python 3.9 follows a hierarchical structure of Actors, the unit that controls each piece of hardware. We used the software framework Codified Likeness Utility to implement each Actor. The Actors communicate with each other through RabbitMQ, which implements the Advanced Message Queuing Protocol. The Actor applies asynchronous programming with non-blocking procedures as the three spectrographs should operate simultaneously. For the requirement of incremental code change and management in the collaboration of the developers, we adopted the SDSS Github Action, which supports continuous integration/continuous deployment. As a result, unit testing with Pytest tested the individual components of the software, respectively, and lab testing with LVMSCP provided the spectra data for the spectrograph calibration. The LVMSCP provides the application programming interface to the Robotic Observation Package to fulfill the required scientific survey execution for the spectrographs.
The Sloan Digital Sky Survey V (SDSS–V) is an all-sky spectroscopic survey of <6 million objects, designed to decode the history of the Milky Way, reveal the inner workings of stars, investigate the origin of solar systems, and track the growth of supermassive black holes across the universe. The Local Volume Mapper (LVM) is a facility designed to provide a contiguous 2500 deg2 integral-field survey over a 3.5 year period from Las Campa˜nas Observatory (LCO) in Chile. The facility comprises four 0.16 m bench-mounted telescopes that feed three multiobject spectrographs with 1801 science fibres, 119 calibration fibres, and 24 sky-background fibres. The fibre cable spans approximately 20 meters from the telescope platform to the spectrograph slits. A sorting hat, located in the spectrograph room, redistributes the 1944 fibres into three 648–element bundles that terminate at the spectrograph slits. In this paper, we briefly summarize the current production progress of the integral-field units, the spectrograph slits, and the sorting hat.
Sloan Digital Sky Survey fifth-generation (SDSS-V) Local Volume Mapper (LVM) is a wide-field IFU survey that uses an array of four 160 mm telescopes. It provides IFU spectra over the optical range with R ∼ 4,000 to reveal the inner components of galaxies and the evolution of the universe. Each telescope observes the science field or the calibration field independently, but all of them should be simultaneously synchronized with the science exposure. To minimize the moving parts, the LVM adopted the siderostat design with a field derotator. We designed the optimized control software for our LVM observation, lvmagp, which controls four focusers, three K-mirror derotators, one fiber selector, four mounts (siderostats), and seven guide cameras. It was built on its owen user interface and messaging protocol called actor and clu based on asynchronous programming. The lvmagp provides three key sequences: autofocus sequence, field acquisition sequence, and autoguide sequence. Also, we designed and fabricated the proto-model siderostat for the software test. The real sky test was made with proto-model siderostat, and the lvmagp showed arcsecond-level field acquisition and autoguide accuracy.
We developed control software for an enclosure system of the SDSS-V Local Volume Mapper (LVM) which provides a contiguous 2,500 deg2 integral-field survey. The LVM enclosure, located at the Las Campanas Observatory in Chile, is a building that hosts the LVM instruments (LVM-I). The enclosure system consists of four main systems: 1) a roll-off dome, 2) building lights, 3) a Heating, Ventilation, and Air Conditioning (HVAC) system, and 4) a safety system. Two Programmable Logic Controllers (PLCs) as middleware software directly operate complex mechanisms of the dome and the HVAC via the Modbus protocol. The LVMECP is implemented by Python 3.9 following the SDSS software framework which adopted a protocol, called CLU, with message passing based on the RabbitMQ and Advanced Message Queuing Protocol (AMQP). Also, we applied asynchronous programming to our system to process multiple requests simultaneously. The Dome PLC system remotely sends commands for the operation of a roll-off dome and enclosure lights. The HVAC PLC system keeps track of changing environmental values of the HVAC system in real-time. This software provides observers with remote access by high-level commands.
The Local Volume Mapper (LVM) project in the fifth iteration of the Sloan Digital Sky Survey (SDSS-Ⅴ) will produce large integral-field spectroscopic survey data to understand the physical conditions of the interstellar medium in the Milky Way, the Magellanic Clouds, and other local-volume galaxies. We developed the Local Volume Mapper Spectrograph Control Package (LVMSCP) which controls the instruments for the operation of the spectrograph. We use the new SDSS message passing protocol CLU (Codified Likeness Utility) for the interaction, based on the RabbitMQ that implemented the Advanced Message Queuing Protocol (AMQP). Also, asynchronous programming with non-blocking procedures is applied for the package since three spectrographs should be operated simultaneously. The software is implemented based on Python 3.9, and will provide the Application Programming Interface (API) to the Robotic Observation Package (ROP) for the integrated observation.
This paper presents an update on the construction, testing, and commissioning of the SDSS-V Local Volume Mapper (LVM) telescope system. LVM is one of three surveys that form the fifth generation of the Sloan Digital Sky Survey, and it will employ a coordinated network of four, 16-cm telescopes feeding three fiber spectrographs at the Las Campanas Observatory. The goal is to spectrally map approximately 2500 square degrees of the Galactic plane with 37” spatial resolution and R~4000 spectral resolution over the wavelength range 360-980 nm. LVM will also target the Magellanic Clouds and other Local Group galaxies. Each of the four LVM telescopes consists of a two-mirror siderostat in alt-alt configuration feeding an optical breadboard. This produces a fixed, stable focal plane for the fiber-based Integral Field Unit (IFU). One telescope hosts the science IFU, while two others observe adjacent fields to calibrate geocoronal emission. The fourth telescope makes rapid observations of bright stars to compensate telluric absorption. The entrance slits of the spectrographs intersperse the fibers from all three types of telescope, producing truly simultaneous science and calibration exposures. We summarize the final design of the telescope system and report on its construction, alignment and testing in the laboratory. We also describe our deployment plan for commissioning at LCO, anticipated for late 2022.
The Sloan Digital Sky Survey V (SDSS-V) is an all-sky spectroscopic survey of <6 million objects, designed to decode the history of the Milky Way, reveal the inner working of the stars, investigate the origin of solar systems, and track the growth of supermassive black holes across the Universe. The Local Volume Mapper (LVM) is one of three surveys that form SDSS-V, and it consists of four telescopes optimized for broad visible-wavelength coverage of 360-980 nm feeding three fiber-fed R∼4000 spectrographs. Each telescope comprises a siderostat and an optical table that hosts powered refracting optics in a triplet configuration, hardware for image de-rotation, image acquisition and guiding systems, and a focal plane assembly. The optical design of LVM balances the science requirements for broad wavelength coverage and spaxel size with the focal ratio imposed by the spectrograph fibers and microlenses. Initial design was completed and optimized in Zemax OpticStudio software. The resulting lenses were fabricated by a vendor and assembled at Carnegie Observatories. Final testing will be on-sky at Las Campanas Observatory in Chile during commissioning in 2022. The assembly process includes bonding of the triplet lenses using Dow Corning SYLGARD 184 Silicone Elastomer (“Sylgard 184”) and mounting in a cell that travels on a motorized focusing stage on the optical table. We present details of the Sylgard 184 bonding process, a basic bonding procedure, recovery from a stress feature in two bonds, and removal of Sylgard during imperfect applications.
This plenary presentation, "Sloan Digital Sky Survey," was prepared for the Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray conference at SPIE Astronomical Telescopes + Instrumentation 2022.
The Extreme-ultraviolet Stellar Characterization for Atmospheric Physics and Evolution (ESCAPE) mission is an astrophysics Small Explorer employing ultraviolet spectroscopy (EUV: 80 to 825 Å and FUV: 1280 to 1650 Å) to explore the high-energy radiation environment in the habitable zones around nearby stars. ESCAPE provides the first comprehensive study of the stellar EUV and coronal mass ejection environments that directly impact the habitability of rocky exoplanets. In a 20-month science mission, ESCAPE will provide the essential stellar characterization to identify exoplanetary systems most conducive to habitability and provide a roadmap for NASA’s future life-finder missions. ESCAPE accomplishes this goal with roughly two-order-of-magnitude gains in EUV efficiency over previous missions. ESCAPE employs a grazing incidence telescope that feeds an EUV and FUV spectrograph. The ESCAPE science instrument builds on previous ultraviolet and x-ray instrumentation, grazing incidence optical systems, and photon-counting ultraviolet detectors used on NASA astrophysics, heliophysics, and planetary science missions. The ESCAPE spacecraft bus is the versatile and high-heritage Ball Aerospace BCP-Small spacecraft. Data archives will be housed at the Mikulski Archive for Space Telescopes.
The Extreme-ultraviolet Stellar Characterization for Atmospheric Physics and Evolution (ESCAPE) mission is an astrophysics Small Explorer employing ultraviolet spectroscopy (EUV: 80 - 825 Å and FUV: 1280 - 1650 Å) to explore the high-energy radiation environment in the habitable zones around nearby stars. ESCAPE provides the first comprehensive study of the stellar EUV and coronal mass ejection environments which directly impact the habitability of rocky exoplanets. In a 20 month science mission, ESCAPE will provide the essential stellar characterization to identify exoplanetary systems most conducive to habitability and provide a roadmap for NASA's future life-finder missions. ESCAPE accomplishes this goal with roughly two-order-of-magnitude gains in EUV efficiency over previous missions. ESCAPE employs a grazing incidence telescope that feeds an EUV and FUV spectrograph. The ESCAPE science instrument builds on previous ultraviolet and X-ray instrumentation, grazing incidence optical systems, and photon-counting ultraviolet detectors used on NASA astrophysics, heliophysics, and planetary science missions. The ESCAPE spacecraft bus is the versatile and high-heritage Ball Aerospace BCP-Small spacecraft. Data archives will be housed at the Mikulski Archive for Space Telescopes (MAST). ESCAPE is currently completing a NASA Phase A study, and if selected for Phase B development would launch in 2025.
The Sloan Digital Sky Survey V (SDSS-V) is an all-sky spectroscopic survey of >6 million objects, designed to decode the history of the Milky Way, reveal the inner workings of stars, investigate the origin of solar systems, and track the growth of supermassive black holes across the Universe. The Local Volume Mapper (LVM) is a facility designed to provide a contiguous 2500 deg2 integral-field survey over a 3.5 year period from Las Campanas Observatory (LCO) in Chile. The facility comprises four small (16 cm) telescopes that deliver science, calibration, and spectro-photometric light to three bench-mounted multi-object spectrographs, designed and build by Winlight Systems. All four telescopes will be equipped with a microlens array integral-field unit (IFU) to slice the focal plane into 35–arcsec large spatial elements while maintaining near-telecentric coupling at the fiber input. The science IFU comprises 1801 fibers, additional 143 fibers are allocated for sky-background and spectro-photometric calibration, totaling 1944 fibers. Each spectrograph will be fed by 648 fibers, which are reformatted into a linear array, forming the entrance slit. In this paper, we present the opto-mechanical design of the LVM-LCO fiber cable system.
The Extreme-ultraviolet Stellar Characterization for Atmospheric Physics and Evolution (ESCAPE) mission is an astrophysics Small Explorer employing ultraviolet spectroscopy (EUV: 80 – 825 Å and FUV: 1280 – 1650 Å) to explore the high-energy radiation environment in the habitable zones around nearby stars. ESCAPE provides the first comprehensive study of the stellar EUV and coronal mass ejection environments which directly impact the habitability of rocky exoplanets. In a 21 month science mission, ESCAPE will provide the essential stellar characterization to identify exoplanetary systems most conducive to habitability and provide a roadmap for future life-finder missions. ESCAPE accomplishes this goal with roughly two-order-of-magnitude gains in EUV efficiency over previous missions. ESCAPE employs a grazing incidence telescope that feeds an EUV and FUV spectrograph, building on experience with ultraviolet and X-ray instrumentation, grazing incidence optical systems, and photon-counting ultraviolet detectors. The instrument builds on design and hardware heritage from numerous NASA UV astrophysics, heliophysics, and planetary science missions. The ESCAPE spacecraft bus is the versatile and high-heritage Ball Aerospace BCP-Smallspacecraft. Data archives are housed at the Mikulski Archive for Space Telescopes (MAST).
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.
The Sloan Digital Sky Survey V (SDSS-V) is an all-sky spectroscopic survey of <6 million objects, designed to decode the history of the Milky Way, reveal the inner workings of stars, investigate the origin of solar systems, and track the growth of supermassive black holes across the Universe. The Local Volume Mapper (LVM) is a facility designed to provide a contiguous 2,500 deg2 integral-field survey over a 3.5 year period from Las Campanas Observatory in Chile. In this paper we provide an overview and status update for the LVM instrument (hereafter LVM-I). Each integral-field unit’s spaxel probes linear scales that are sub-parsec (Milky Way) to ∼10 pc (Magellanic Clouds) which is accomplished with an angular diameter of 36.900. LVM’s spectral resolution is R = λ/∆λ ∼ 4, 000 which probes velocities of 33 kms−1 (1 σ) from 365 nm to 950 nm. LVM uses four 16-cm telescopes feeding three spectrographs. One telescope carries the bulk of the science load with ∼1,800 fibers coupled to the field via a pair of lenslet arrays, two telescopes are used to measure the night sky spectra in fields that flank the science field, and a fourth telescope contemporaneously monitors bright standard stars to determine atmospheric extinction. We expect LVM-I to deliver percent-level precision on important line ratios down to a few Rayleigh. The three spectrographs are being built by Winlight corporation in France based on those for the Dark Energy Spectroscopic Instrument (DESI). In this paper we present the high-level system design of LVM-I including the lenslet-coupled fiber IFUs, telescopes, guiding+acquisition system, calibration systems, enclosures, and spectrographs.
The Sloan Digital Sky Survey V (SDSS-V) is an all-sky spectroscopic survey of <6 million objects, designed to decode the history of the Milky Way, reveal the inner workings of stars, investigate the origin of solar systems, and track the growth of supermassive black holes across the Universe. The Local Volume Mapper (LVM) is one of three surveys that form SDSS-V. LVM will employ a coordinated system of four telescopes feeding three fiber spectrographs at Las Campanas Observatory in Chile. The goal is to map approximately 2500 square degrees of the Galactic plane over the wavelength range 360-980 nm with R~4000 spectral resolution. These observations will reveal for the first time how distinct gaseous environments within the Galaxy interact with each other and with the stellar population, producing the large-scale interstellar medium that we observe. Accurately mapping and calibrating a substantial portion of the sky at this spatial resolution requires a unique type of telescope system. Each of the four LVM telescopes has a diameter of 16 cm, making them considerably smaller and lighter than the instruments they feed. One telescope will host the science IFU containing ~1800 fibers arranged in a close-packed hexagon. Two additional Calibration telescopes will observe fields adjacent to the science IFU, in order to calibrate out terrestrial airglow and other geo-coronal emission. The fourth, Spectrophotometric telescope will make rapid observations of bright stars (typically 12 during a single IFU / Calibration exposure) to correct for telluric absorption lines and overall extinction. The fibers from all three types of telescope will be interspersed in the entrance slits of the spectrographs, allowing for simultaneous science and calibration exposures. Although considerably smaller than the next generation of giants, the LVM telescopes must also operate close to the limits of physical optics, and the geometry and scope of the LVM survey present unique challenges. For example, with this type of telescope at the Las Campanas site, the effects of optical aberrations, diffraction, seeing, and (uncorrected) atmospheric dispersion are all of comparable scale. This, coupled with the need for repeated and reliable measurements over years, leads to some unconventional design choices. This paper presents the preliminary design of the LVM telescope system and discusses the requirements and tradeoffs that led to the baseline choices.
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.
The long-term stability of exoplanetary atmospheres depends critically on the extreme-ultraviolet (EUV) flux from the host star. The EUV flux likely controls the demographics of the short-period planet population as well the ability for rocky planets to maintain habitable environments long enough for the emergence of life. We present the Extreme-ultraviolet Stellar Characterization for Atmospheric Physics and Evolution (ESCAPE) mission, an astrophysics Small Explorer proposed to NASA. ESCAPE employs extreme- and far-ultraviolet spectroscopy (70 - 1800 Α) to characterize the highenergy radiation environment in the habitable zones (HZs) around nearby stars. ESCAPE provides the first comprehensive study of the stellar EUV environments that control atmospheric mass-loss and determine the habitability of rocky exoplanets. The ESCAPE instrument comprises an EUV grazing incidence telescope feeding four diffraction gratings and a photon-counting detector. The telescope is 50 cm diameter with four nested parabolic primary mirrors and four nested elliptical secondary mirrors, fabricated and aligned by NASA Marshall Space Flight Center and the Smithsonian Astrophysical Observatory. The off-plane grating assemblies are fabricated at Pennsylvania State University and the ESCAPE detector system is a micro-channel plate (MCP; 125mm x 40mm active area) sensor developed by the University of California, Berkeley. ESCAPE employs the versatile and high-heritage Ball Aerospace BCP-100 spacecraft.
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.
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.
The Visible Integral Field Replicable Unit Spectrograph (VIRUS), the instrument for the Hobby Eberly Telescope Dark Energy Experiment (HETDEX), consists of 78 replicable units, each with two integral field spectrographs. The VIRUS design takes advantage of large-scale replication of simple units to significantly reduce engineering and production costs of building a facility instrument of this scale. With VIRUS being 156 realizations of the same spectrograph, this paper uncovers the statistical variations in production of these units. Lab relative throughput measures are compared with independently measured grating and optical element performance allowing for potential diagnosis for the cause of variation due to spectrograph elements. Based on variations in performance of individual optical components, throughput curves are simulated for 156 VIRUS spectrograph channels. Once delivered, each unit is paired with a fiber bundle and throughput measurements are made on sky using twilight flats. We compare throughput variance from on-sky measurements to the simulated throughputs. We find that the variation in throughput matches that predicted by modeling of the individual optics performance. This paper presents the results for the 40 VIRUS units now deployed.
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.
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.
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 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.
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.
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.
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 conceptual design for a high-resolution optical spectrograph appropriate for mounting at Cassegrain on a large aperture telescope. The design is based on our work for the Gemini High Resolution Optical Spectrograph (CUGHOS) project. Our design places the spectrograph at Cassegrain focus to maximize throughput and blue wavelength coverage, delivering R=40,000 resolving power over a continuous 320–1050 nm waveband with throughputs twice those of current instruments. The optical design uses a two-arm, cross-dispersed echelle format with each arm optimized to maximize efficiency. A fixed image slicer is used to minimize optics sizes. The principal challenge for the instrument design is to minimize flexure and degradation of the optical image. To ensure image stability, our opto-mechanical design combines a cost-effective, passively stable bench employing a honeycomb aluminum structure with active flexure control. The active flexure compensation consists of hexapod mounts for each focal plane with full 6-axis range of motion capability to correct for focus and beam displacement. We verified instrument performance using an integrated model that couples the optical and mechanical design to image performance. The full end-to-end modeling of the system under gravitational, thermal, and vibrational perturbations shows that deflections of the optical beam at the focal plane are <29 μm per exposure under the worst case scenario (<10 μm for most orientations), with final correction to 5 μm or better using open-loop active control to meet the stability requirement. The design elements and high fidelity modeling process are generally applicable to instruments requiring high stability under a varying gravity vector.
The Cosmic Origins Spectrograph (COS) was installed into the Hubble Space Telescope (HST) during Servicing
Mission 4 (SM4) in May 2009. COS is designed to obtain spectra of faint objects at moderate spectral resolution (R >
16,000) in two channels: FUV, covering wavelengths from 1150 to 1450 Å; and NUV, covering 1700 - 3200 Å. Two
low resolution gratings (R > 1500) cover the < 900 - 2050 Å (FUV) and 1650 - 3200 Å (NUV) wavelength regions. An
imaging capability is also available on the NUV channel.
As part of the Hubble Servicing Mission Observatory Verification (SMOV) program, an extensive period of checkout,
fine-tuning and preliminary characterization began after the installation of COS. The COS SMOV program was a
cooperative effort between the Space Telescope Science Institute and the Instrument Definition Team based at the
University of Colorado. Nearly 2800 COS exposures in 34 separate observing programs were obtained during the course
of SMOV. Early activities included an initial instrument functional checkout, turn-on and initial characterization of the
detectors, NUV and FUV channel focus and alignment, and target acquisition verification and assessment. Once this
initial period was completed, science-related calibrations and verifications were performed in order to prepare the
instrument for normal science operations. These activities included wavelength calibration, flux calibration, detector flat
field characterization, spectroscopic performance verification, high S/N operation, and thermal and structural stability
measurements. We discuss the design, execution and results of the SMOV program, including the interrelationships
between the various tasks, and how the pre-launch plan was adjusted in real-time due to changing conditions.
The Cosmic Origins Spectrograph,1 COS, will be installed in the Hubble Space Telescope (HST) during the next
servicing mission. This will be the most sensitive ultraviolet spectrograph ever flown aboard the HST.
The calibration pipeline (CALCOS), written in Python, has been developed by the Space Telescope Science
Institute (STScI) to support the calibration of HST/COS data. As with other HST pipelines, CALCOS uses an
association table to specify the data files to be included, and employs header keywords to specify the calibration
steps to be performed and the reference files to be used.
CALCOS is designed with a common underlying structure for processing far ultraviolet (FUV) and near
ultraviolet (NUV) channels which, respectively, use a cross delay line and a Multi Anode Microchannel Array
(MAMA) detector. The pipeline basics and channel dependent specifics are presented. The generation and
application of the current reference files, derived from ground-based calibration data, is described, along with
the pipeline verification process and results.
The CALCOS calibration includes pulse-height filtering and geometric correction for the FUV channel; flat-field,
deadtime, and Doppler correction for both channels. Methods for obtaining an accurate wavelength calibra-tion
using the on-board spectral line lamp are described. The instrument sensitivity is applied to the background
corrected spectrum to produce the final flux calibrated spectrum.
High resolution spectroscopy is the foundation for many of the most challenging and productive
of all astronomical observations. A highly precise, repeatable and stable wavelength calibration
is especially essential for long term RV observations. The two wavelength references
in wide use for visible wavelengths, iodine absorption cells and thorium/argon lamps, each
have fundamental limitations which restrict their ultimate utility.
We are exploring the possibility of adapting emerging laser frequency comb technology in development
at the National Institute of Standards and Technology in Boulder, Colorado, to the
needs of high resolution, high stability astronomical spectroscopy. This technology has the
potential to extend the two current wavelength standards both in terms of spectral coverage and
in terms of long term precision, ultimately enabling better than 10 cm/s astronomical radial
velocity determination.
We have completed a conceptual design study of the High Resolution Optical Spectrograph for the Thirty Meter Telescope project. We propose the use of a fiber fed integral field unit and a dichroic tree to achieve R=100,000 spectroscopy from 310 to 1100 nm independent of AO performance. The system relies on the dichroic tree to provide coarse wavelength selection, and 32 first order spectro-graph benches. This approach allows for simultaneous optimization of grating and detector performance for all wavelengths, resulting in high efficiency, near uniform dispersion, and reduced program risk and cost due to the high degree of component commonality. We present projected performance and design details.
We present a conceptual design for a High Resolution Optical Spectrograph (HROS) for the Thirty Meter Telescope, a 30-m primary aperture ground-based telescope currently under development (www.tmt.org). To decouple downstream optics sizes from the size of the seeing disk and/or AO performance, we use fiber fed IFUs to generate a 0.1" pseudo-slit. The use of multiple IFUs instead of a slit also allows for spatially resolved spectroscopy, multi-object spectroscopy, positionable sky sampling, and insertion of a simultaneous wavelength calibration signal into the beam. Instead of a cross-dispersed echelle design, our concept uses a dichroic tree to provide spectral separation. The dichroics feed 32 independent first-order spectrographs that cover the 310 to 1100 nm optical waveband at a nominal spectral resolution of R=100,000. This approach allows for the optimization of coatings and on-blaze grating performance in each channel, resulting in high efficiency, near-uniform dispersion, and reduced program risk and cost due to the high degree of component commonality. We also discuss the general applicability of this concept for achieving high resolution spectroscopy in the next generation of ground-based instrumentation.
A second generation near-infrared instrument was built by the University of Colorado for the ARC 3.5 meter telescope and is being commissioned at the Apache Point Observatory. An initial engineering run, first light, commissioning observations, and initial facility science operations have been accomplished in the last year. Instrument imaging performance was good to excellent from first light and consortium observers began to employ the instrument on a shared-risk basis immediately after commissioning operations. Instrument optical and mechanical performance during this testing and operations phase are discussed. Detector system (Rockwell Hawaii-1RG 1024x1024 HgCdTe focal plane array with Leach controller) characteristics during these early operations are detailed along with ongoing efforts for system optimization. High resolution (R~10,000) spectroscopy is planned employing a Queensgate (now IC Optical) cryogenic Fabry-Perot etalon, though mechanical difficulties with the etalon precluded a system performance demonstration. The Consortium has decided that the instrument will retain the name NIC-FPS (Near Infrared Camera and Fabry-Perot Spectrometer) after commissioning.
A near-infrared instrument is being built for the ARC 3.5 meter telescope that will operate in both an imaging and a narrow band, full field spectroscopic mode. The 4.5' x 4.5' fild-of-view is imaged onto a new-generation, low-noise Rockwell Hawaii-1RG 1024x1024 HgCdTe detector. High resolution (R~10,000) spectroscopy is accomplished by employing a Queensgate (now IC Optical) cryogenic Fabry-Perot etalon. The instrument is housed in a large Dewar of innovative, light-weight design. This report describes the as-built opto-mechanical system for the instrument and the work remaining before deployment at Apache Point Observatory in New Mexico.
We present the preliminary calibration results for the Cosmic Origins Spectrograph, a fourth generation replacement instrument for the Hubble Space Telescope due to be installed in mid-2005. The Cosmic Origins Spectrograph consists of two spectroscopic channels: a far ultraviolet channel that observes wavelengths between 1150 and 2000 Åand a near ultraviolet channel that observes between 1700 and 3200 Å. Each channel supports moderate (R≈20,000) and low (R≈2000) spectral resolution. We discuss the calibration methodology, test configurations, and preliminary end-to-end calibration results. This includes spectral resolution, system efficiency, flat fields, and wavelength scales for each channel. We also present the measured transmission of the Bright Object Aperture (BOA) and the measured spatial resolution.
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