APOGEE

APOGEE
Sloan Digital Sky Survey · CC BY 4.0 · source
Name	APOGEE
Operator	Sloan Digital Sky Survey Consortium
Location	Apache Point Observatory
Wavelength	Near-infrared (H-band)
Aperture	2.5 m (Sloan Foundation Telescope)
First light	2011
Status	Completed (APOGEE-1/2)

APOGEE is a high-resolution, near-infrared stellar spectroscopic survey conducted as part of the Sloan Digital Sky Survey program. The project obtained multiplexed, high signal-to-noise H-band spectra of hundreds of thousands of stars to trace the chemical and kinematic structure of the Milky Way across the Galactic center, Galactic bulge, Galactic disk, and Galactic halo. APOGEE data supported studies in stellar astrophysics, Galactic archaeology, and chemodynamical evolution, interfacing with projects such as Gaia, Kepler, TESS, and the Large Synoptic Survey Telescope initiatives.

Overview

APOGEE was designed within the framework of the Sloan Digital Sky Survey to address questions about the formation and evolution of the Milky Way by measuring precise radial velocities and detailed chemical abundances for large stellar samples. The survey operated in multiple phases, including APOGEE-1 and APOGEE-2, coordinated by institutions such as the University of Virginia, University of Washington, New Mexico State University, and the Carnegie Institution for Science. APOGEE complemented optical spectroscopic programs like SEGUE and photometric efforts like the Two Micron All Sky Survey and the Wide-field Infrared Survey Explorer.

Instrumentation and Survey Design

The core instrument was a cryogenic, high-resolution, near-infrared spectrograph fed by fiber bundles on the Sloan Foundation Telescope at Apache Point Observatory, with a twin instrument later deployed at Las Campanas Observatory. The spectrograph delivered R~22,500 spectra across the H-band using three detectors and an innovative optical fiber feed, enabling simultaneous observation of 300 targets per plate. The design drew expertise from teams at University of Arizona, Lawrence Berkeley National Laboratory, Harvard–Smithsonian Center for Astrophysics, and industrial partners. Calibration relied on techniques and standards associated with IRAF, radial velocity standards tied to the International Celestial Reference Frame, and throughput monitoring analogous to procedures used by SDSS-III and SDSS-IV.

Target Selection and Observing Strategy

Target selection employed color–magnitude cuts based on 2MASS photometry and targeted giants across different Galactic components, with specialized selection for fields near the Galactic center, open clusters like M67 and globular clusters such as M13 for calibration. The survey strategy balanced deep plates for faint bulge targets with bright plates for disk and halo science, adopting visit cadences tailored for radial velocity stability and binarity detection, integrating constraints from GALEX and WISE catalogs. Observing campaigns coordinated with site operations at Apache Point Observatory and Las Campanas Observatory, following scheduling practices used by the Sloan Digital Sky Survey and leveraging community-led proposals.

Data Processing and Products

Data reduction pipelines produced one-dimensional, wavelength-calibrated spectra, radial velocities, and stellar parameters using automated analysis frameworks developed by collaborations including teams at Yale University and Institute for Astronomy, University of Hawaii. Abundance determination employed synthetic spectral fitting against model atmospheres from groups such as MARCS and Kurucz, yielding multi-element abundances (e.g., C, N, O, Mg, Si, Fe) with precision useful for chemodynamical modeling. APOGEE data releases were integrated into the SDSS data archives, interoperable with catalogs from Gaia DR2, Kepler Input Catalog, and LAMOST, and were accompanied by value-added catalogs produced by working groups associated with institutions like The Ohio State University and Max Planck Institute for Astronomy.

Scientific Results

APOGEE enabled discoveries about radial and vertical abundance gradients in the Galactic disk, chemically distinct populations in the Galactic bulge, and accretion signatures in the Galactic halo attributable to merger events analogous to those inferred from studies of the Sagittarius Dwarf Spheroidal Galaxy and theoretical predictions from the Lambda-CDM framework. Results refined the age–metallicity relation through comparisons with asteroseismic ages from Kepler and K2 missions, informed stellar mixing and nucleosynthesis studies tied to models by Burbidge et al. and Woosley & Weaver, and constrained disk radial migration scenarios discussed by authors such as Sellwood & Binney. APOGEE measurements of stellar kinematics complemented proper motion catalogs from Gaia to map chemodynamical substructure like streams and moving groups similar to features observed in the GD-1 and Orphan streams.

Collaborations and Legacy Projects

APOGEE was conducted by a collaboration spanning universities and observatories including University of California, Berkeley, University of Cambridge, Princeton University, and national laboratories like Brookhaven National Laboratory. Legacy projects and follow-ups built on APOGEE included targeted surveys and instrumentation efforts such as the APOGEE-2S southern survey, synergies with the GALAH survey and the WEAVE project, and planning inputs to future facilities like the Thirty Meter Telescope and the European Extremely Large Telescope. APOGEE data continue to underpin archival research in stellar populations, informing proposals across observatories such as Gemini Observatory and Keck Observatory and contributing to graduate and postdoctoral research at institutions like University of Colorado Boulder and Carnegie Mellon University.

Category:Spectroscopic surveys Category:Sloan Digital Sky Survey projects Category:Galactic astronomy