96 research outputs found
The Multi-object, Fiber-fed Spectrographs for the Sloan Digital Sky Survey and the Baryon Oscillation Spectroscopic Survey
We present the design and performance of the multi-object fiber spectrographs for the Sloan Digital Sky Survey (SDSS) and their upgrade for the Baryon Oscillation Spectroscopic Survey (BOSS). Originally commissioned in Fall 1999 on the 2.5 m aperture Sloan Telescope at Apache Point Observatory, the spectrographs produced more than 1.5 million spectra for the SDSS and SDSS-II surveys, enabling a wide variety of Galactic and extra-galactic science including the first observation of baryon acoustic oscillations in 2005. The spectrographs were upgraded in 2009 and are currently in use for BOSS, the flagship survey of the third-generation SDSS-III project. BOSS will measure redshifts of 1.35 million massive galaxies to redshift 0.7 and Lyα absorption of 160,000 high redshift quasars over 10,000 deg^2 of sky, making percent level measurements of the absolute cosmic distance scale of the universe and placing tight constraints on the equation of state of dark energy. The twin multi-object fiber spectrographs utilize a simple optical layout with reflective collimators, gratings, all-refractive cameras, and state-of-the-art CCD detectors to produce hundreds of spectra simultaneously in two channels over a bandpass covering the near-ultraviolet to the near-infrared, with a resolving power R = λ/FWHM ~ 2000. Building on proven heritage, the spectrographs were upgraded for BOSS with volume-phase holographic gratings and modern CCD detectors, improving the peak throughput by nearly a factor of two, extending the bandpass to cover 360 nm < λ < 1000 nm, and increasing the number of fibers from 640 to 1000 per exposure. In this paper we describe the original SDSS spectrograph design and the upgrades implemented for BOSS, and document the predicted and measured performances
Ground-Based Astronomical Instrumentation Development in the United States: A White Paper on the Challenges Faced by the US Community
This invited white paper, submitted to the National Science Foundation in
January of 2020, discusses the current challenges faced by the United States
astronomical instrumentation community in the era of extremely large
telescopes. Some details may have changed since submission, but the basic
tenets are still very much valid. The paper summarizes the technical, funding,
and personnel challenges the US community faces, provides an informal census of
current instrumentation groups in the US, and compares the state-of-affairs in
the US with that of the European community, which builds astronomical
instruments from consortia of large hard-money funded instrument centers in a
coordinated fashion. With the recent release of the Decadal Survey on Astronomy
and Astrophysics 2020 (Astro2020), it is clear that strong community support
exists for this next generation of large telescopes in the US. Is the US ready?
Is there sufficient talent, facilities, and resources in the community today to
meet the challenge of developing the complex suite of instruments envisioned
for two US ELTs? These questions are addressed, along with thoughts on how the
National Science Foundation can help build a more viable and stable
instrumentation program in the US. These thoughts are intended to serve as a
starting point for a broader discussion, with the end goal being a plan that
puts the US astronomical instrumentation community on solid footing and poised
to take on the challenges presented by the ambitious goals we have set in the
era of ELTs.Comment: 22 pages, 1 table, 0 figures. This is an invited white paper
submitted to the National Science Foundation in January of 202
Visible camera cryostat design and performance for the SuMIRe Prime Focus Spectrograph (PFS)
We describe the design and performance of the SuMIRe Prime Focus Spectrograph
(PFS) visible camera cryostats. SuMIRe PFS is a massively multi-plexed
ground-based spectrograph consisting of four identical spectrograph modules,
each receiving roughly 600 fibers from a 2394 fiber robotic positioner at the
prime focus. Each spectrograph module has three channels covering wavelength
ranges 380~nm -- 640~nm, 640~nm -- 955~nm, and 955~nm -- 1.26~um, with the
dispersed light being imaged in each channel by a f/1.07 vacuum Schmidt camera.
The cameras are very large, having a clear aperture of 300~mm at the entrance
window, and a mass of 280~kg. In this paper we describe the design of the
visible camera cryostats and discuss various aspects of cryostat performance
JWST's Cryogenic Position Metrology System
The James Webb Space Telescope will undergo a full system test in the cryogenic vacuum chamber A at the Johnson Spaceflight Center in order to verify the overall performance of the combined telescope and instrument suite. This will be the largest and most extensive cryogenic test ever undertaken. Early in the test system development, it was determined that precise position measurements of the overall hardware would enhance the test results. Various concepts were considered before selecting photogrammetry for this metrology. Photogrammetry has been used in space systems for decades, however cryogenic use combined with the size and the optical/thermal sensitivity of JWST creates a unique set of implementation challenges. This paper provides an overview of the JWST photogrammetric system and mitigation strategies for three key engineering design challenges: 1) the thermal design of the viewing windows to prevent excessive heat leak and stray light to the test article 2) cost effective motors and mechanisms to provide the angle diversity required, and 3) camera-flash life and reliability sufficient for inaccessible use during the number and duration of the cryogenic tests
Detectors and cryostat design for the SuMIRe Prime Focus Spectrograph (PFS)
We describe the conceptual design of the camera cryostats, detectors, and
detector readout electronics for the SuMIRe Prime Focus Spectrograph (PFS)
being developed for the Subaru telescope. The SuMIRe PFS will consist of four
identical spectrographs, each receiving 600 fibers from a 2400 fiber robotic
positioner at the prime focus. Each spectrograph will have three channels
covering wavelength ranges 3800 {\AA} - 6700 {\AA}, 6500 {\AA} - 10000 {\AA},
and 9700 {\AA} - 13000 {\AA}, with the dispersed light being imaged in each
channel by a f/1.10 vacuum Schmidt camera. In the blue and red channels a pair
of Hamamatsu 2K x 4K edge-buttable CCDs with 15 um pixels are used to form a 4K
x 4K array. For the IR channel, the new Teledyne 4K x 4K, 15 um pixel,
mercury-cadmium-telluride sensor with substrate removed for short-wavelength
response and a 1.7 um cutoff will be used. Identical detector geometry and a
nearly identical optical design allow for a common cryostat design with the
only notable difference being the need for a cold radiation shield in the IR
camera to mitigate thermal background. This paper describes the details of the
cryostat design and cooling scheme, relevant thermal considerations and
analysis, and discusses the detectors and detector readout electronics
The Sloan Digital Sky Survey Quasar Catalog I. Early Data Release
We present the first edition of the Sloan Digital Sky Survey (SDSS) Quasar
Catalog. The catalog consists of the 3814 objects (3000 discovered by the SDSS)
in the initial SDSS public data release that have at least one emission line
with a full width at half maximum larger than 1000 km/s, luminosities brighter
than M_i^* = -23, and highly reliable redshifts. The area covered by the
catalog is 494 square degrees; the majority of the objects were found in SDSS
commissioning data using a multicolor selection technique. The quasar redshifts
range from 0.15 to 5.03. For each object the catalog presents positions
accurate to better than 0.2" rms per coordinate, five band (ugriz) CCD-based
photometry with typical accuracy of 0.05 mag, radio and X-ray emission
properties, and information on the morphology and selection method. Calibrated
spectra of all objects in the catalog, covering the wavelength region 3800 to
9200 Angstroms at a spectral resolution of 1800-2100, are also available. Since
the quasars were selected during the commissioning period, a time when the
quasar selection algorithm was undergoing frequent revisions, the sample is not
homogeneous and is not intended for statistical analysis.Comment: 27 pages, 4 figures, 4 tables, accepted by A
Colors of 2625 Quasars at 0<z<5 Measured in the Sloan Digital Sky Survey Photometric System
We present an empirical investigation of the colors of quasars in the Sloan
Digital Sky Survey (SDSS) photometric system. The sample studied includes 2625
quasars with SDSS photometry. The quasars are distributed in a 2.5 degree wide
stripe centered on the Celestial Equator covering square degrees.
Positions and SDSS magnitudes are given for the 898 quasars known prior to SDSS
spectroscopic commissioning. New SDSS quasars represent an increase of over
200% in the number of known quasars in this area of the sky. The ensemble
average of the observed colors of quasars in the SDSS passbands are well
represented by a power-law continuum with (). However, the contributions of the bump
and other strong emission lines have a significant effect upon the colors. The
color-redshift relation exhibits considerable structure, which may be of use in
determining photometric redshifts for quasars. The range of colors can be
accounted for by a range in the optical spectral index with a distribution
(95% confidence), but there is a red tail in the
distribution. This tail may be a sign of internal reddening. Finally, we show
that there is a continuum of properties between quasars and Seyfert galaxies
and we test the validity of the traditional division between the two classes of
AGN.Comment: 66 pages, 15 figures (3 color), accepted by A
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