The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 sq deg will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. We will describe the extensive preparations of the Mayall telescope and its environs for DESI, and will report on progress-to-date of the installation of DESI itself.
The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 square degrees will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. We present an overview of the instrumentation, the main technical requirements and challenges, and the current status of the project.
The Dark Energy Spectroscopic Instrument (DESI), currently under construction, is designed to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 40 million galaxies over 14000 sq deg will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. This paper describes the overall design and construction status of the prime focus corrector. The size and complexity of the system poses significant design and production challenges. The optics of the corrector consists of six lenses, ranging from 0.8 - 1.14m in diameter, two of which can be rotated to act as an atmospheric dispersion corrector. These lenses are mounted in custom cells that themselves are mounted in a barrel assembly the alignment of which can be actively controlled by a hexapod system to micrometer precision. The whole assembly will be mounted at the prime focus of the Mayall 4m telescope at Kitt Peak observatory and will be one of the largest lens systems ever built for an optical telescope. Construction of the corrector began in 2014 and is well advanced. The system is due to be delivered to the telescope for installation in early 2018.
The Dark Energy Spectroscopic Instrument (DESI), which is currently under construction, is designed to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 40 million galaxies over 14000 sq deg will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fibre optic positioners. The fibres in turn feed ten broad-band spectrographs. The prime focus corrector for DESI consists of six lenses that range in diameter from 0.80 - 1.14 meters and from 83 - 237 kg in weight. The alignment of the large lenses of the optical corrector poses a significant challenge as in order to meet the fibre throughput requirements they have to be aligned to within a tolerance of ~50 micrometres. This paper details the design for the cells that will hold the lenses and the alignment and assembly procedure for the mounting of the lenses into the cells and into the complete barrel assembly. This is based on the experience obtained from the alignment of the Dark Energy Camera (DECam) instrument which was successfully assembled and aligned by the same team and we include in the paper the lessons learnt and design modifications that will be implemented on the DESI system.
The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 40 million galaxies over 14,000 sq. deg. will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. We describe the ProtoDESI experiment, planned for installation and commissioning at the Mayall telescope in the fall of 2016, which will test the fiber positioning system for DESI. The ProtoDESI focal plate, consisting of 10 fiber positioners, illuminated fiducials, and a guide, focus and alignment (GFA) sensor module, will be installed behind the existing Mosaic prime focus corrector. A Fiber View Camera (FVC) will be mounted to the lower surface of the primary mirror cell and a subset of the Instrument Control System (ICS) will control the ProtoDESI subsystems, communicate with the Telescope Control System (TCS), and collect instrument monitoring data. Short optical fibers from the positioners will be routed to the back of the focal plane where they will be imaged by the Fiber Photometry Camera (FPC) or back-illuminated by a LED system. Target objects will be identified relative to guide stars, and using the GFA in a control loop with the ICS/TCS system, the guide stars will remain stable on pre-identified GFA pixels. The fiber positioners will then be commanded to the target locations and placed on the targets iteratively, using the FVC to centroid on back-illuminated fibers and fiducials to make corrective delta motions. When the positioners are aligned with the targets on-sky, the FPC will measure the intensities from the positioners’ fibers which can then be dithered to look for intensity changes, indicating how well the fibers were initially positioned on target centers. The final goal is to operate ProtoDESI on the Mayall telescope for a 6-hour period during one night, successfully placing targets on the intended fibers for the duration of a typical DESI science exposure.
The Dark Energy Spectroscopic Instrument (DESI) is under construction and will be used to measure the expansion history of the Universe using the Baryon Acoustic Oscillation (BAO) technique and the growth of structure using redshift-space distortions (RSD). The spectra of 30 million galaxies over 14000 sq deg will be measured over the course of the experiment. In order to provide spectroscopic targets for the DESI survey, we are carrying out a three-band (g,r,z ) imaging survey of the sky using the NOAO 4-m telescopes at Kitt Peak National Observatory (KPNO) and the Cerro Tololo Interamerican Observatory (CTIO). At KPNO, we will use an upgraded version of the Mayall 4m telescope prime focus camera, Mosaic3, to carry out a z-band survey of the Northern Galactic Cap at declinations δ≥+30 degrees. By equipping an existing Dewar with four 4kx4k fully depleted CCDs manufactured by the Lawrence Berkeley National Laboratory (LBNL), we increased the z-band throughput of the system by a factor of 1.6. These devices have the thickest active area fielded at a telescope. The Mosaic3 z-band survey will be complemented by g-band and r-band observations using the Bok telescope and 90 Prime imager on Kitt Peak. We describe the upgrade and performance of the Mosaic3 instrument and the scope of the northern survey.
The Dark Energy Spectroscopic Instrument, to be located at the prime focus of the Mayall telescope, includes a wide field corrector, a 5000 fiber positioner system, and a fiber view camera. The mapping of the sky to the focal plane, needed to position the fibers accurately, is described in detail. A major challenge is dealing with the large amount of distortion introduced by the optics (of order 10% scale change), including time-dependent non-axisymmetric distortions introduced by the atmospheric dispersion compensator. Solutions are presented to measure or mitigate these effects.
Motivated by a desire to improve the KPNO Mayall 4m telescope’s pointing and tracking performance prior to the start of the DESI installation and by a need to improve the maintainability of its telescope control system (TCS), we recently completed a major modernization of that system based heavily on recent changes made at the CTIO Blanco 4m, as described by Warner et al (2012). We describe here the things we did differently from the Blanco upgrade. We also present results from the as-built performance of the new servo and pointing systems.
The Dark Energy Spectroscopic Instrument (DESI) is under construction for installation on the Mayall 4 Meter telescope. The use of a liquid cooling system is proposed to maintain the DESI prime focus assembly temperature within ±1°C of ambient. Due to concerns of fluid deposition onto optical surfaces from possible leaks, systematic tests were performed of the effects on first surface aluminized mirrors of ethylene glycol and two other candidate coolants. Objective measurement of scattering and reflectivity was an important supplement to visual inspection. Rapid cleanup of a coolant spill followed by a hand wash of the mirror limited surface degradation to the equivalent of a few months of general environmental exposure. Prolonged exposure to corrosive coolants dissolved the aluminum, necesitating mirror recoating.
The Mayall 4-meter telescope recently went through a major modernization of its telescope control system in preparation for DESI. We describe MPK (Mayall Pointing Kernel), our new software for telescope control. MPK outputs a 20Hz position-based trajectory with a velocity component, which feeds into Mayall’s new servo system over a socket. We wrote a simple yet realistic servo simulator that let us develop MPK mostly without access to real hardware, and also lets us provide other teams with a Mayall simulator as test bed for development of new instruments. MPK has a small core comprised of prioritized, soft real-time threads. Access to the core’s services is via MPK’s main thread, a complete, interactive Tcl/Tk shell, which gives us the power and flexibility of a scripting language to add any other features, from GUIs, to modules for interaction with critical subsystems like dome or guider, to an API for networked clients of a new instrument (e.g., DESI). MPK is designed for long term maintainability: it runs on a stock computer and Linux OS, and uses only standard, open source libraries, except for commercial software that comes with source code in ANSI C/C++. We discuss the technical details of how MPK combines the Reflexxes motion library with the TCSpk/TPK pointing library to generically handle any motion requests, from slews to offsets to sidereal or non-sidereal tracking. We show how MPK calculates when the servos have reached a steady state. We also discuss our TPOINT modeling strategy and report performance results.
The Dark Energy Spectroscopic instrument (DESI) is a 5000 fiber multi-object spectrometer system under development
for installation on the National Optical Astronomy Observatory (NOAO) Kitt Peak 4m telescope (the Mayall telescope).
DESI is designed to perform a 14,000° (square) galaxy and Quasi-Stellar Object (QSO) redshift survey to improve
estimates of the dark energy equation of state. The survey design imposes numerous constraints on a prime focus
corrector design, including field of view, geometrical blur, stability, fiber injection efficiency, zenith angle, mass and
cost. The DESI baseline wide-field optical design described herein provides a 3.2° diameter field of view with six 0.8-
1.14m diameter lenses and an integral atmospheric dispersion compensator.
TripleSpec 4 (TS4) is a near-infrared (0.8um to 2.45um) moderate resolution (R ~ 3200) cross-dispersed spectrograph
for the 4m Blanco Telescope that simultaneously measures the Y, J, H and K bands for objects reimaged
within its slit. TS4 is being built by Cornell University and NOAO with scheduled commissioning in 2015.
TS4 is a near replica of the previous TripleSpec designs for Apache Point Observatory's ARC 3.5m, Palomar
5m and Keck 10m telescopes, but includes adjustments and improvements to the slit, fore-optics, coatings and
the detector. We discuss the changes to the TripleSpec design as well as the fabrication status and expected
sensitivity of TS4.
The KPNO Nicholas U. Mayall 4-meter telescope is to be the host facility for the Dark Energy Spectroscopic Instrument (DESI). DESI will record broadband spectra simultaneously for 5000 objects distributed over a 3-degree diameter field of view; it will record the spectra of approximately 20 million galaxies and quasi-stellar objects during a five-year survey. This survey will improve the combined precision of measurement on the dark energy equation of state today (w<sub>0</sub>) and its evolution with redshift (w<sub>a</sub>) by approximately a factor of ten over existing spectroscopy baryon acoustic oscillation surveys (e.g., BOSS<sup>1</sup>) in both co-moving volume surveyed and number of galaxies mapped. Installation of DESI on the telescope is a complex procedure, involving a complete replacement of the telescope top end, routing of massive fiber cables, and installation of banks of spectrographs in an environmentally-controlled lab area within the dome. Furthermore, assembly of the instrument and major subsystems must be carried out on-site given their size and complexity. A detailed installation plan is being developed early in the project in order to ensure that DESI and its subsystems are designed so they can be safely and efficiently installed, and to ensure that all telescope and facility modifications required to enable installation are identified and completed in time.
We describe the design, construction and measured performance of the Kitt Peak Ohio State Multi-Object Spectrograph
(KOSMOS) for the 4-m Mayall telescope and the Cerro Tololo Ohio State Multi-Object Spectrograph (COSMOS) for
the 4-m Blanco telescope. These nearly identical imaging spectrographs are modified versions of the OSMOS
instrument; they provide a pair of new, high-efficiency instruments to the NOAO user community. KOSMOS and
COSMOS may be used for imaging, long-slit, and multi-slit spectroscopy over a 100 square arcminute field of view with
a pixel scale of 0.29 arcseconds. Each contains two VPH grisms that provide R~2500 with a one arcsecond slit and their
wavelengths of peak diffraction efficiency are approximately 510nm and 750nm. Both may also be used with either a
thin, blue-optimized CCD from e2v or a thick, fully depleted, red-optimized CCD from LBNL. These instruments were
developed in response to the ReSTAR process. KOSMOS was commissioned in 2013B and COSMOS was
commissioned in 2014A.
The High-resolution Near-infrared Spectrograph (HRNIRS) concept for the Gemini telescopes combines a seeing-limited R ~ 70000 cross-dispersed mode and a MCAO-fed near diffraction-limited R ~ 20000 multi-object mode into a single compact instrument operating over the 0.9-5.5μm range. We describe the mechanical design, emphasizing the challenging design requirements and how they were met. The approach of developing the optical and mechanical designs in concert and utilizing proven working concepts from the Gemini Near Infra-Red Spectrograph were key elements of the design philosophy. Liang, et al. provides a detailed discussion of the optical design, Hinkle, et al. describes the science cases and requirements as well as a general overview, and Eikenberry, et al. describes the systems engineering and performance aspects of HRNIRS.
HRNIRS is an extremely versatile high-resolution infrared facility spectrograph designed for the Gemini South telescope. Operating over the 1.05 - 5.5 micron wavelength range, it has the capability to carry out a wide range of scientific programs by incorporating two separate modes of operation. The first is a conventional single slit cross-dispersed mode providing spectral resolution R ~ 70000 with a 0.4 arcsec slit over as much as an octave in wavelength, thus covering most of the JHK or LM windows in a single observation. In this mode the spectrograph accepts the Gemini seeing-limited f/16 input over a small field. A built-in modulator and polarizer allow HRNIRS to measure both linear and circular polarization. The second mode is a moderately-high resolution (R ~ 30000) spectrograph observing multiple objects simultaneously within a 2 arcmin field fed by the f/33.2 Gemini MCAO beam. In this paper, we discuss the optical design considerations, present the resulting design and show that the predicted performance meets the design requirements.
The High-Resolution Near-InfraRed Spectrograph (HRNIRS) concept for the Gemini telescopes combines a seeing limited R ~ 70000 cross-dispersed mode and an MCAO-fed near diffraction-limited R ~ 30000 multi-object mode into a single compact instrument operating over the 1 - 5 μm range. The HRNIRS concept was developed in response to proposals issued through the Aspen instrument process by Gemini. Here we review the science drivers and key functional requirements. We present a general overview of the instrument and estimate the limiting performance.
The High-resolution Near-infrared Spectrograph (HRNIRS) concept for the Gemini telescopes combines a seeing-limited R ~ 7000 cross-dispersed mode and an MCAO-fed near diffraction-limited R ~ 20000 multi-object mode into a single compact instrument operating over the 0.9 - 5.5 μm range. We describe the systems engineering and performance modeling aspects of this study, emphasizing simulations of high-precision radial verlocity measurements in the Gemini Cassegrain-focus instrument environment.
Current instruments and plans for new instruments for the W.M. Keck Observatory are reviewed on behalf of the Keck Science Steering Committee. Much has happened in the last two years. Both 10-meter telescopes have been in full operation for some time and each has a significant complement of instruments. Adaptive optics systems are functioning on both telescopes, the Keck II laser guide star system has been tested, and the Keck Interferometer has achieved first fringes. The existing LRIS spectrograph on Keck I has been upgraded to provide a UV/blue optimized channel and two new instruments have been delivered within the past year, namely, DEIMOS, a multi-object spectrograph and NIRC2, a diffraction-limited IR camera. A near-infrared integral field unit spectrometer for AO is currently under development, as is a CCD detector upgrade for the existing HIRES spectrograph. Future plans include detector upgrades for LRIS-R, and a powerful wide-field near-IR multi-object spectrometer.
We present the design for a recently approved instrument for the Keck Telescope. Called OSIRIS, it was inspired by the optical spectrograph TIGER of R. Bacon et al. and will utilize an infrared transmissive lenslet array to sample a rectangular field of view at close to the Keck diffraction limit. By packing the spectra very closely together (2 pixel rows per spectrum) and using the Rockwell Hawaii-2 detector (wavelengths between 1 and 2.5 microns), we will achieve a relatively large field of view (up to 6."4) while maintaining full broad-band spectral coverage at a resolution of 3900. Due to the extremely low backgrounds between night sky lines and at AO spatial samplings, the instrument will reach point source sensitivities several times fainter than any existing infrared spectrograph. We are also coupling a separate infrared AO camera dubbed SHARC to work as an acquisition camera and to monitor the point spread function's behavior during long spectroscopic exposures. Among the challenges of the instrument are: a fully cryogenic design, four spatial resolutions from 0."02 to 0."10, large aluminum optics for the spectrography, extremely repeatable spectral formats and a sophisticated data reduction pipeline.
The Keck II Adaptive Optics system and the NIRC2 camera provide a unique facility for high angular resolution imaging and spectroscopy in the near infrared. In this paper, we present the result of a unique project to map the entire surface of Io in the thermal infrared (Lp band centered at 3.8 μm). This project was undertaken by a team from the W. M. Keck Observatory and UC Berkeley to illustrate the power of this instrumentation. The 75-milliarcsec-resolution images, corresponding to ~200 km of linear spatial resolution on Io, have been combined to build a thermal infrared map of the entire satellite. We have identified 26 hot spots including one that was undetected by the Galileo mission. A movie and a Java applet featuring a volcanically active rotating satellite were created.