The Apache Point Observatory Galactic Evolution Experiment (APOGEE) Spectrographs


Wilson JC, Hearty FR, Skrutskie MF, Majewski SR, Holtzman JA, Eisenstein D, Gunn J, Blank B, Henderson C, Smee S, et al. The Apache Point Observatory Galactic Evolution Experiment (APOGEE) Spectrographs. Publications of the Astronomical Society of the Pacific [Internet]. 2019;131 :055001.

Date Published:

May 01, 2019


We describe the design and performance of the near-infrared (1.51-1.70μm), fiber-fed, multi-object (300 fibers), high resolution (R = λ/∆λ ̃22,500) spectrograph built for the Apache Point Observatory GalacticEvolution Experiment (APOGEE). APOGEE is a survey of ̃105 redgiant stars that systematically sampled all Milky Way populations(bulge, disk, and halo) to study the Galaxy’s chemical and kinematicalhistory. It was part of the Sloan Digital Sky Survey III (SDSS-III) from2011 to 2014 using the 2.5 m Sloan Foundation Telescope at Apache PointObservatory, New Mexico. The APOGEE-2 survey is now using thespectrograph as part of SDSS-IV, as well as a second spectrograph, aclose copy of the first, operating at the 2.5 m du Pont Telescope at LasCampanas Observatory in Chile. Although several fiber-fed, multi-object,high resolution spectrographs have been built for visual wavelengthspectroscopy, the APOGEE spectrograph is one of the first suchinstruments built for observations in the near-infrared. Theinstrument’s successful development was enabled by several keyinnovations, including a “gang connector” to allow simultaneousconnections of 300 fibers; hermetically sealed feedthroughs to allowfibers to pass through the cryostat wall continuously; the firstcryogenically deployed mosaic volume phase holographic grating; and alarge refractive camera that includes mono-crystalline silicon and fusedsilica elements with diameters as large as ̃400 mm. This paper containsa comprehensive description of all aspects of the instrument includingthe fiber system, optics and opto-mechanics, detector arrays, mechanicsand cryogenics, instrument control, calibration system, opticalperformance and stability, lessons learned, and design changes for thesecond instrument.