[Show abstract][Hide abstract] ABSTRACT: The Prime Focus Spectrograph (PFS) is a major instrument under development
for the 8.2 m Subaru telescope. Four identical spectrograph modules are located
in a room above one Nasmyth focus. A 55~m fiber optic cable feeds light to the
spectrographs from a robotic positioner at the prime focus, behind the
wide-field corrector developed for Hyper Suprime-Cam. The positioner contains
2400 fibers and covers a 1.3~degree hexagonal field of view.
The spectrograph optical design consists of a Schmidt collimator, two
dichroic beamsplitters to split the light into three channels, and for each
channel a volume phase holographic (VPH) grating and a dual-corrector, modified
Schmidt reimaging camera. This design provides a 275~mm collimated beam
diameter, wide simultaneous wavelength coverage from 380~nm to 1.26~\textmu m,
and good imaging performance at the fast f/1.05 focal ratio required from the
cameras to avoid oversampling the fibers. The three channels are designated as
the blue, red, and near-infrared (NIR), and cover the bandpasses 380--650~nm
(blue), 630--970~nm (red), and 0.94--1.26~\textmu m (NIR). A mosaic of two
Hamamatsu 2k$\times$4k, 15~\textmu m pixel CCDs records the spectra in the blue
and red channels, while the NIR channel employs a 4k$\times$4k,
substrate-removed HAWAII-4RG array from Teledyne, with 15~\textmu m pixels and
a 1.7~\textmu m wavelength cutoff.
VPH gratings were an obvious choice for PFS and a set of three prototype VPH
gratings (one each of the blue, red, and NIR designs) was ordered and has been
recently delivered. In this paper we present the design and specifications for
the PFS gratings, the plan and setups used for testing both the prototype and
final gratings, and results from recent optical testing of the prototype
[Show abstract][Hide abstract] ABSTRACT: Building on the legacy of the Sloan Digital Sky Survey (SDSS-I and II), SDSS-III is a program of four spectroscopic surveys on three scientific themes: dark energy and cosmological parameters, the history and structure of the Milky Way, and the population of giant planets around other stars. In keeping with SDSS tradition, SDSS-III will provide regular public releases of all its data, beginning with SDSS Data Release 8 (DR8), which was made public in 2011 January and includes SDSS-I and SDSS-II images and spectra reprocessed with the latest pipelines and calibrations produced for the SDSS-III investigations. This paper presents an overview of the four surveys that comprise SDSS-III. The Baryon Oscillation Spectroscopic Survey will measure redshifts of 1.5 million massive galaxies and Lyα forest spectra of 150,000 quasars, using the baryon acoustic oscillation feature of large-scale structure to obtain percent-level determinations of the distance scale and Hubble expansion rate at z < 0.7 and at z 2.5. SEGUE-2, an already completed SDSS-III survey that is the continuation of the SDSS-II Sloan Extension for Galactic Understanding and Exploration (SEGUE), measured medium-resolution (R = λ/Δλ 1800) optical spectra of 118,000 stars in a variety of target categories, probing chemical evolution, stellar kinematics and substructure, and the mass profile of the dark matter halo from the solar neighborhood to distances of 100 kpc. APOGEE, the Apache Point Observatory Galactic Evolution Experiment, will obtain high-resolution (R 30,000), high signal-to-noise ratio (S/N ≥ 100 per resolution element), H-band (1.51 μm < λ < 1.70 μm) spectra of 105 evolved, late-type stars, measuring separate abundances for ~15 elements per star and creating the first high-precision spectroscopic survey of all Galactic stellar populations (bulge, bar, disks, halo) with a uniform set of stellar tracers and spectral diagnostics. The Multi-object APO Radial Velocity Exoplanet Large-area Survey (MARVELS) will monitor radial velocities of more than 8000 FGK stars with the sensitivity and cadence (10-40 m s–1, ~24 visits per star) needed to detect giant planets with periods up to two years, providing an unprecedented data set for understanding the formation and dynamical evolution of giant planet systems. As of 2011 January, SDSS-III has obtained spectra of more than 240,000 galaxies, 29,000 z ≥ 2.2 quasars, and 140,000 stars, including 74,000 velocity measurements of 2580 stars for MARVELS.
The Astronomical Journal 08/2011; 142(3):72. · 4.97 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Volume phase holographic (VPH) gratings are increasingly being used as diffractive elements in astronomical instruments due to their potential for very high peak diffraction efficiencies and the possibility of a compact instrument design when the gratings are used in transmission. Historically, VPH grating (VPHG) sizes have been limited by the size of manufacturer's holographic recording optics. We report on the design, specification and fabrication of a large, 290 mm × 475 mm elliptically-shaped, mosaic VPHG for the Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectrograph. This high-resolution near-infrared multi-object spectrograph is in construction for the Sloan Digital Sky Survey III (SDSS III). The 1008.6 lines/mm VPHG was designed for optimized performance over a wavelength range from 1.5 to 1.7 mum. A step-and-repeat exposure method was chosen to fabricate a three-segment mosaic on a 305 mm × 508 mm monolithic fused-silica substrate. Specification considerations imposed on the VPHG to assure the mosaic construction will satisfy the end use requirements are discussed. Production issues and test results of the mosaic VPHG are discussed.