John Wilson, F. Hearty, M. Skrutskie, S. Majewski, R. Schiavon, D. Eisenstein, J. Gunn, J. Holtzman, D. Nidever, B. Gillespie, D. Weinberg, B. Blank, C. Henderson, S. Smee, R. Barkhouser, A. Harding, S. Hope, G. Fitzgerald, T. Stolberg, J. Arns, M. Nelson, S. Brunner, A. Burton, E. Walker, C. Lam, P. Maseman, J. Barr, F. Leger, L. Carey, N. MacDonald, G. Ebelke, S. Beland, T. Horne, E. Young, G. Rieke, M. Rieke, T. O'Brien, J. Crane, M. Carr, C. Harrison, R. Stoll, M. Vernieri, M. Shetrone, C. Allende-Prieto, J. Johnson, P. Frinchaboy, G. Zasowski, A. Garcia Perez, D. Bizyaev, K. Cunha, V. Smith, Sz. Meszaros, B. Zhao, M. Hayden, S. D. Chojnowski, B. Andrews, C. Loomis, R. Owen, M. Klaene, J. Brinkmann, F. Stauffer, D. Long, W. Jordan, D. Holder, F. Cope, T. Naugle, B. Pfaffenberger, D. Schlegel, M. Blanton, D. Muna, B. Weaver, S. Snedden, K. Pan, H. Brewington, E. Malanushenko, V. Malanushenko, A. Simmons, D. Oravetz, S. Mahadevan, S. Halverson
The Apache Point Observatory Galactic Evolution Experiment (APOGEE) uses a dedicated 300-fiber, narrow-band
near-infrared (1.51-1.7 μm), high resolution (R~22,500) spectrograph to survey approximately 100,000 giant stars across
the Milky Way. This three-year survey, in operation since late-summer 2011 as part of the Sloan Digital Sky Survey III
(SDSS III), will revolutionize our understanding of the kinematical and chemical enrichment histories of all Galactic
stellar populations. We present the performance of the instrument from its first year in operation. The instrument is
housed in a separate building adjacent to the 2.5-m SDSS telescope and fed light via approximately 45-meter fiber runs
from the telescope. The instrument design includes numerous innovations including a gang connector that allows
simultaneous connection of all fibers with a single plug to a telescope cartridge that positions the fibers on the sky,
numerous places in the fiber train in which focal ratio degradation had to be minimized, a large mosaic-VPH (290 mm x
475 mm elliptically-shaped recorded area), an f/1.4 six-element refractive camera featuring silicon and fused silica
elements with diameters as large as 393 mm, three near-infrared detectors mounted in a 1 x 3 mosaic with sub-pixel
translation capability, and all of these components housed within a custom, LN2-cooled, stainless steel vacuum cryostat
with dimensions 1.4-m x 2.3-m x 1.3-m.
Development of the Apache Point Observatory Galactic Evolution Experiment (APOGEE) near-infrared spectrograph
has motivated thorough investigation into the properties and performance of optical fibers. The fiber selected for
APOGEE is a step index, multi-mode fiber, developed by PolyMicro, with a 120μm low OH, fused silica core, 25μm
cladding, and 10μm buffer. The instrument design includes a 40 meter fiber run, connecting the spectrograph to the
2.5m Sloan Digital Sky Survey (SDSS) telescope, and an additional 2.5 meter fiber segment located within the
instrument dewar, a vacuum-sealed, cryogenic environment. This light path is convoluted and includes many transitions
and connections where the beam is susceptible irrevocable loss. To optimize the spectrograph performance it is
necessary to minimize the losses incurred in the fiber system, especially those resulting in focal ratio degradation (FRD).
The focus of this research has been to identify potential sources of loss and where applicable, select material components
to minimize this effect. There is little previous documented work concerning the performance of optical fibers within
this wavelength band (1.5-1.7μm). Consequently, the following includes comprehensive explanations of the APOGEE
fiber system components, our experimental design and optical test bed set-up, beam alignment procedures, fiber
terminating and polishing techniques, and results from our examination of FRD as correlated with source wavelength,
fiber length and termination, and environmental conditions.
The Apache Point Observatory Galactic Evolution Experiment (APOGEE) will use a dedicated 300-fiber, narrow-band
(1.5-1.7 micron), high resolution (R~30,000), near-infrared spectrograph to survey approximately 100,000 giant stars
across the Milky Way. This survey, conducted as part of the Sloan Digital Sky Survey III (SDSS III), will revolutionize
our understanding of kinematical and chemical enrichment histories of all Galactic stellar populations. The instrument,
currently in fabrication, will be housed in a separate building adjacent to the 2.5 m SDSS telescope and fed light via
approximately 45-meter fiber runs from the telescope. The instrument design includes numerous technological
challenges and innovations including a gang connector that allows simultaneous connection of all fibers with a single
plug to a telescope cartridge that positions the fibers on the sky, numerous places in the fiber train in which focal ratio
degradation must be minimized, a large (290 mm x 475 mm elliptically-shaped recorded area) mosaic-VPH, an f/1.4 sixelement
refractive camera featuring silicon and fused silica elements with diameters as large as 393 mm, three near-within a custom, LN2-cooled, stainless steel vacuum cryostat with dimensions 1.4 m x 2.3 m x 1.3 m.
This paper will describe the concerns, parameters and restrictions in the design and construction of the instrument rotator used on the SDSS telescope.
The rotator provides support for two 600 Lb. Spectrographs, through all axes motion, without causing harmful radial moments to be translated to its inner ring which supports the mosaic imaging camera. This is accomplished using an outer-inner ring design. The outer ring is a thin-walled box structure incorporating the drive surface and is attached to the inner ring through a steel membrane. This rotator design requires the telescope’s primary support structure to provide final structural integrity. Due to this feature, a special fixture was needed to transport the rotator from the vendor and to install it onto the telescope.
Positional accuracy and feedback is provided by an optical tape and read-head system manufactured by Heidenhain and attached to the inner ring. The drive motor was designed to use the same motor as those employed for the other two telescope axes, thus minimizing the spare-parts inventory and maintenance. Its drive pinion is of a pinch design, with the pinion axis parallel to rotator radius. A great deal of attention and planning was required in the construction of the box frame outer ring and the induction heat-treating of the drive surface.
Drive surface tolerances were maintained within +/-0.001 inches, and internal stress cracks from heat-treating were minimal.
The support and position control systems for both the primary and secondary mirror of the SDSS Telescope allow the mirrors up to 12 mm of precisely positioned axial motion, as well as limited tilt and transverse motion. This paper describes the final design and operation of these systems. Some relative strengths and limitations of the components and problems encountered with their implementation are also summarized.
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