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 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 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 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 (w0) and its evolution with redshift (wa) by approximately a factor of ten over existing spectroscopy baryon acoustic oscillation surveys (e.g., BOSS1) 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.
[The BigBOSS experiment is a redshift survey designed to map the large scale structure of the universe and probe the nature of dark energy. Using massively-multiplexed _ber spectroscopy over 14,000 deg2 of sky, the survey will deliver more than 20 million galaxy and quasar redshifts. The resulting three dimensional sky map will contain signatures from primordial baryon acoustic oscillations (BAO) that set a "standard ruler" distance scale. Using the BAO signature, BigBOSS will measure the cosmological distance scale to < 1% accuracy from 0.5<z<3.0, shedding new light on the expansion history and growth of large scale structure in the Universe at a time when dark energy began to dominate. In this work, we give an overview of the BigBOSS survey goals and methodology, focusing on measuring the [O II] λ3727 emission line doublet from star-forming galaxies. We detail a new spectral simulation tool used in generating BigBOSS observations for emission-line galaxy targets. We perform a trade study of the detected galaxy redshift distribution under two observational cases relative to the baseline survey and discuss the impact on the BigBOSS science goal.
BigBOSS is a proposed ground-based dark energy experiment to study baryon acoustic oscillations (BAO) and the
growth of large scale structure. It consists of a fiber-fed multi-object spectrograph designed to be installed on the Mayall
4-meter telescope at Kitt Peak, Arizona. BigBOSS includes an optical corrector assembly and 5000-fiber-positioner
focal plane assembly that replace the existing Mayall prime focus hardware. 40-meter long optical fiber bundles are
routed from the focal plane, through the telescope declination and right ascension pivots, to spectrographs in the
thermally insulated FTS Laboratory, immediately adjacent to the telescope. Each of the ten spectrographs includes three
separate spectral bands. The FTS Laboratory also houses support electronics, cooling, and vacuum equipment. The
prime focus assembly includes mounts for the existing Mayall f/8 secondary mirror to allow observations with
Cassegrain instruments. We describe the major elements of the BigBOSS instrument, plans for integrating with the
Telescope, and proposed modifications and additions to existing Mayall facilities.
BigBOSS is a Stage IV dark energy experiment based on proven techniques to study baryon acoustic oscillations and the growth of large scale structure. The 2010 Astronomy and Astrophysics Decadal Survey labeled dark energy as a key area of exploration. BigBOSS is designed to perform a 14,000 square degree survey of 20 million galaxies and quasi-stellar objects. The project involves installation of a new instrument on the Mayall 4m telescope, operated by the National Optical
Astronomy Observatory. The instrument includes a new optical widefield corrector, a 5,000 fiber actuator system, and a multi-object spectrometer. Systems engineering flowdown from data set requirements to instrument requirements are discussed, along with the trade considerations and a pre-conceptual baseline design of the widefield optical corrector, spectrometer and fiber positioner systems.
BigBOSS is a proposed DOE-NSF Stage IV ground-based dark energy experiment designed to study
baryon acoustic oscillations (BAO) and the growth of large scale structure with a 14,000 square
degree survey of the redshifts of galaxies and quasi-stellar objects. The project involves
modification of existing facilities operated by the National Optical Astronomy Observatory
(NOAO). Design and systems engineering of a preliminary 3 degree field of view refractive
corrector, atmospheric dispersion corrector (ADC), and 5000 actuator fiber positioning system are
In March and April 2003, the Chandra X-ray Observatory carried out a
series of 126 short observations (5 ksec each) covering a continuous
area of the Bootes constellation to construct a large area shallow
X-ray survey. These observations were carried out as collaboration of
Guest Observer (C. Jones PI) and Guaranteed Time Observer (S. Murray
PI) programs. We present here, in Paper I, an initial analysis of the
survey data and the source detection process, showing the sky
coverage, exposure map, and some of the collective properties of the
resulting catalog of sources. The Bo\"otes area was selected to
overlap a well studied region where optical, and radio data, to
sufficient depth, have already been obtained making the identification
of candidate counterparts straight forward. In 5 ksec, we reach a
limiting flux of ≈10-3ct s-1 (corresponding to ≈10-14 erg cm-2s-10.5-7.0 keV). We examine the spatial distribution of the sources in this ~9.3 square degree survey region using several techniques to search for evidence of cosmic variance in the X-ray source density on scales as small as the ACIS-I field of view
(~16x16 arc minutes). With follow up optical spectroscopy using the MMT/Hectospec, we can obtain spectroscopic redshifts for about 1/3 - 1./2 of the X-ray sources, which can be used to look for evidence of large scale structures traced by AGN associated with the cosmic web.
A design is described for a potential new facility capable of taking detailed spectroscopy of millions of objects in the Universe to explore the complexity of the Universe and to answer fundamental questions relating to the equation of state of dark energy and to how the Milky Way galaxy formed. The specific design described is envisioned for implementation on the Gemini 8-meter telescopes. It utilizes a 1.5° field of view and samples that field with up to ~5000 apertures. This Kilo-Aperture Optical Spectrograph (KAOS) is mounted at prime focus with a 4-element corrector, atmospheric dispersion compensator (ADC), and an Echidna-style fiber optic positioner. The ADC doubles as a wobble plate, allowing fast guiding that cancels out the wind buffeting of the telescope. The fibers, which can be reconfigured in less than 10 minutes, feed to an array of 12 spectrographs located in the pier of the telescope. The spectrographs are capable of provided spectral resolving powers of a few thousand up to about 40,000.
High redshift radio galaxies are great cosmological tools for pinpointing the most massive objects in the early Universe: massive forming galaxies, active super-massive black holes and proto-clusters. We report on deep narrow-band imaging and spectroscopic observations of several z > 2 radio galaxy fields to investigate the nature of giant Ly-α nebulae centered on the galaxies and to search for over-dense regions around them. We discuss the possible implications for our understanding of the formation and evolution of massive galaxies and galaxy clusters.
We are exploring the feasibility of a very large telescope with a wide field of view for multi-object spectroscopic surveys. This paper presents a brief overview of the scientific need for such facility, a possible optical design for such a telescope, and a description of how such a telescope might function for both wide-field, seeing-limited spectroscopy and narrow-field, high-Strehl imaging and spectroscopy. The science is primarily driven by the fact that imaging surveys are now capable of cataloguing vast numbers of targets that would take a formidable amount of time on currently existing telescopes for spectroscopic followup. The telescope design, a 4-mirror extension of the Paul concept, is a 30-meter telescope that delivers a full 1 degree(s) field at f/4 with excellent image performance across the full field. The primary is an f/1, 30-meter. The secondary has a diameter of 5.3-meters and contains a pure conic surface that delivers an uncorrected focus between the primary and secondary. The tertiary mirror is located at the vertex of the primary and has a diameter of about 10.6- meters. The quaternary mirror, located at the position of the initial focus, is about 4.4-meters and images the final focus back at the vertex of the tertiary mirror. The initial design had both the tertiary and quaternary mirrors with high-order, even aspheric surfaces. Further study has led to a simplification of the design in which the tertiary is now a pure conic like the primary and secondary mirrors, and the quaternary mirror is something like a Schmidt corrector with only modest fourth and sixth order terms.
The confluence of advances in telescope and spectrograph design computing power, pathfinding imaging capabilities on the ground and in space, and the maturity of many astrophysical fields, allow us to look beyond the study of a few unique objects and towards the systematic study of large samples in order to completely characterize their properties, formation history, and cosmological significance. These studies require spectroscopic observations to probe the kinematics, chemical composition, dynamics, ages, masses and evolutionary histories of astronomical objects. Examples of three fundamental science goals are described that demand a wide-field system on a large telescope.