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| APOGEE-2S | |
|---|---|
| Name | APOGEE-2S |
| Mission | Ground-based astronomical spectroscopic survey |
| Operators | Apache Point Observatory, Las Campanas Observatory, Sloan Digital Sky Survey |
| Instruments | Near-infrared spectrograph |
| Wavelength | Near-infrared H-band (1.5–1.7 μm) |
| Telescopes | 2.5-meter Sloan Telescope, 2.5 m du Pont Telescope, Magellan Telescopes |
| Start | 2017 |
| Status | Operational (survey phase) |
APOGEE-2S is the southern component of a high-resolution, near-infrared stellar spectroscopic survey developed within the Sloan Digital Sky Survey program. The project extends a northern survey to the southern celestial hemisphere using facilities at Las Campanas Observatory and partnerships with southern observatories, enabling chemical and kinematic mapping of the Milky Way's disk, bulge, and halo. APOGEE-2S integrates hardware, software, and collaboration models rooted in established large surveys to produce uniformly calibrated spectra and stellar parameters for hundreds of thousands of stars.
APOGEE-2S operates as part of a broader effort by the Sloan Digital Sky Survey to produce high-resolution spectroscopy across both hemispheres, complementing northern observations performed at Apache Point Observatory. The southern program employs a cryogenic, multi-object, fiber-fed near-infrared spectrograph designed to observe through interstellar dust toward regions such as the Galactic Center, Large Magellanic Cloud, and Small Magellanic Cloud. Goals include mapping metallicity gradients implicated in the formation histories probed by comparisons to surveys like Gaia and to legacy projects such as RAVE, LAMOST, and SEGUE.
The APOGEE-2S spectrograph is a high-resolution (R~22,000) instrument optimized for the H-band, using a cryogenic optical bench, volume-phase holographic gratings, and infrared detectors derived from technologies used at facilities like Gemini Observatory and ESO. Fibers are plugged into drilled plates fabricated to coordinate systems tied to catalogs from missions including Gaia and 2MASS. The fiber system routes light from focal-plane positions on telescopes such as the du Pont Telescope and Magellan Telescopes into the spectrograph housed in a temperature-controlled enclosure, mirroring approaches applied in instruments like FLAMES and AAOmega.
APOGEE-2S employs a tiered targeting strategy that prioritizes red giant branch stars, red clump stars, and other luminous evolved populations across sightlines selected to probe the Galactic bulge, Galactic disk, and Galactic halo. Target selection algorithms cross-match photometry from 2MASS, proper motions from Gaia, and ancillary catalogs produced by collaborations with teams associated with Spitzer Space Telescope and WISE. The survey uses a mixture of fields: long, deep visits for the Galactic Center and shorter, wide-area tiles for the southern disk and satellite galaxies like the Large Magellanic Cloud and Small Magellanic Cloud. Coordination with time-domain programs such as Kepler and TESS allows joint asteroseismic and spectroscopic analyses.
Raw data from APOGEE-2S are processed through an automated pipeline adapted from methods developed for the northern instrument, incorporating extraction, wavelength calibration, sky subtraction, and telluric correction. Calibration employs observations of hot, featureless standards and nightly lamps following practices used at ESO and NOIRLab facilities. Stellar parameters (Teff, log g, [Fe/H]) and individual abundances are derived using spectral synthesis and model-atmosphere grids comparable to those utilized in programs like GALAH and techniques pioneered in spectroscopic analyses for Kepler targets. Cross-validation leverages stars in common with Gaia and with high-resolution studies from instruments such as UVES and HIRES.
Primary scientific goals include reconstructing the Milky Way's formation history through chemo-dynamical tagging, measuring abundance gradients across structural components, and characterizing stellar populations in nearby satellites such as the Large Magellanic Cloud. Early APOGEE-2S results have refined metallicity and alpha-element trends in the inner disk and bulge, provided constraints on radial migration comparable to interpretations from Gaia kinematics, and improved inventories of stellar parameters for membership studies of globular clusters like Omega Centauri and dwarf galaxies similar to Fornax. The survey has also contributed to studies of stellar evolution by supplying abundances for stars observed by Kepler and K2, enabling age-abundance relations essential for Galactic archaeology.
APOGEE-2S is managed through collaboration among institutions in the Sloan Digital Sky Survey consortium, southern observatories, and international partners from universities and national laboratories associated with projects like NOAO and AAO. Operations involve plate drilling, fiber plugging, nightly sequencing, and collaborative data releases coordinated with the SDSS data management teams and archives modeled on the Sloan Digital Sky Survey public data release framework. Cross-survey synergies include joint analyses with Gaia, GALAH, RAVE, and time-domain missions, and cooperative observing campaigns with facilities such as Magellan and ESO telescopes.
Future enhancements anticipate expanded targeting in under-sampled southern sightlines, improved pipelines incorporating machine-learning approaches akin to work in the Gaia-ESO Survey, and integration with next-generation facilities like Vera C. Rubin Observatory for complementary photometry and variability characterization. The APOGEE-2S dataset is intended to form a lasting legacy for Galactic archaeology, providing a homogeneous spectroscopic baseline for comparison with future high-resolution surveys and space missions including Roman Space Telescope and successive Gaia data releases. The southern component's catalogues and spectra will continue to enable studies of chemical evolution, stellar populations, and the assembly history of the Milky Way.
Category:Astronomical surveys