# APOGEE-2

## Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2)

APOGEE-2 extends the sky coverage of the SDSS by using telescopes at both Apache Point Observatory in the United States (APOGEE-2N) and Las Campanas Observatory in Chile (APOGEE-2S). Using telescopes in both hemispheres means that APOGEE-2 is able to observe the entire Milky Way. Image credit: Dana Berry / SkyWorks Digital Inc. and the SDSS collaboration.

The second generation of the Apache Point Observatory Galactic Evolution Experiment (APOGEE-2) observes the "archaeological" record of the Milky Way Galaxy embedded in hundreds of thousands of stars to explore its assembly history and evolution. The details of how the Galaxy evolved are preserved today in the motions and chemical compositions of its stars. APOGEE-2 maps the dynamical and chemical patterns of Milky Way stars with data from the 1-meter NMSU Telescope and the 2.5-meter Sloan Foundation Telescope at the Apache Point Observatory in the United States (APOGEE-2N), and the 2.5-meter du Pont Telescope at Las Campanas Observatory in Chile (APOGEE-2S).

### Key Science Questions

• What is the history of star formation and chemical enrichment of the Milky Way?
• What are the dynamics of the disk, bulge, and halo of the Milky Way?
• What is the age distribution of stars in the Milky Way?
• Do planet-hosting stars have different properties than stars that have no planets?

To answer these science questions, APOGEE-2 relies upon spectroscopy of stars using near-infrared light, which can penetrate regions obscured by interstellar dust. The APOGEE-2 spectral data provide a comprehensive view of (1) element abundance distributions in Galactic stars and (2) the dynamical motions of stars at various locations throughout the Milky Way. For those unfamiliar with these concepts, we have written a primer on spectroscopy in the near-infrared and background on the Milky Way Galaxy.

In SDSS-III, APOGEE-1 predominantly observed red giant stars distributed across several kiloparsecs of the Milky Way disk. APOGEE-2 continues to observe these evolved stars and with the Southern hemisphere component, extends into previously unreachable parts of the Galaxy. APOGEE also acquires spectra of young stars and star-forming regions, variable stars, stars in star clusters and satellite galaxies, and stars with asteroseismic measurements. See APOGEE Targeting Information for more.

## APOGEE-2 Dataset

### APOGEE-2 Technical Details

• Observations at Apache Point Observatory and Las Campanas Observatory
• Duration: August 2014 - January 2021
• Fiber Complement: 300 fibers per 7 deg2 plate (APO 2.5-m, R=$1.5^{\circ}$) or 2.8 deg2 plate (LCO 2.5-m; R=$0.95^{\circ}$); 10 fiber (APO 1-m)
• Wavelength Range: $1.51-1.70 \mu m$
• Spectral Resolution: R$\sim$22,500
• Total Sample Size: 657,000 unique targets
• Signal-to-Noise Goal: S/N $\gt$ 100 per pixel
• Radial Velocity Precision: $\sim$200 m/s
• Elemental Abundance Precision: $\sim$0.1 dex for 20 calibrated species

### Data Releases

The first data release from APOGEE-2 was DR14 presenting new data from 2 years of observations from APOGEE-N. DR16 presented the first data from APOGEE-S (operations began in 2017) and 2 additional years of observation from APOGEE-N. DR17 is the final data release from APOGEE, as a project, and includes an analysis of all observations taken with the APOGEE instruments in SDSS-III APOGEE-1 and SDSS-IV APOGEE-2 using the state-of-the-art data processing and analysis pipelines.
The planned APOGEE survey footprint, overlaid on an infrared image of the Milky Way. The completed APOGEE-1 fields are shown in blue, whereas the proposed APOGEE-2N fields and APOGEE-2S are in orange and yellow, respectively. Image credit: P. M. Frinchaboy, 2MASS (background image)
The final APOGEE DR17 footprint, overlaid on an infrared image of the Milky Way. The APOGEE-1 fields are shown in cyan, APOGEE-2N fields in blue, and APOGEE-2S are in red. Image credit: C. Hayes, 2MASS (Background image)

## APOGEE-2 Team

Principal Investigator
Steve Majewski (UVa)
Survey Scientist
Jon Holtzman (NMSU)
Project Manager
Jennifer Sobeck (UW)
Instrument Scientist
John Wilson (UVa)
Pipeline Coordinator
Matthew Shetrone (McDonald Observatory)
Target Selection Coordinators
North: Drew Chojnowski (NMSU), Chris Hayes (UVa);
South: Felipe Antonio Santana Rojas (Universidad de Chile);
Special Targets & External Programs: Kevin Covey (WWU)
Survey Operations Scientists
North: Nathan De Lee (Northern Kentucky University);
South: Penélope Longa-Peña (Universidad de Antofagasta)
LCO Operations Liaison

### Snapshots of the APOGEE-2 Team

There is also a large team of other people who work to develop pipelines, improve targeting strategies, maintain the instrument, and document the data, among many other tasks that are required for a survey of the size and scale of APOGEE. Below are some snapshots over the 7 years of APOGEE-2 activities.

Team photo from an APOGEE-2 Team meeting held at the Observatories of the Carnegie Institution for Science in 2017. Image courtesy of S. Rubel.
Team photo from the 2018 APOGEE-2 Team Meeting in Besançon, France. The cities of Charlottesville, Virginia (home to the University of Virginia) and Besançon, France (home to the Besançon Astronomical Observatory, a member of the French Participation Group) have a "sister city" relationship, making this a special meeting for the team members at either institution. Image courtesy of A. Robin.
The Targeting Team leads in 2017 at the University of Washington preparing for dual-hemisphere operations at APO and LCO. Image courtesy of J. Fernandez-Trincado.
Team photo from the 2014 joint APOGEE-1 and APOGEE-2 Team Meeting in Virginia.
Team photo taken at the Universidad de La Serena in 2016 during the preparations to bring the new APOGEE-S instrument to Las Campanas Observatory.
Team photo from the 2017 SDSS-IV Collaboration Meeting in Santiago, Chile. This meeting celebrated the expansion of SDSS operations into Chile.
Snapshot from an APOGEE-2 session at the 2016 SDSS-IV Collaboration Meeting at the University of Wisconsin. Image courtesy of C. Hayes.
The APOGEE-2S "Wrap Party" at the conclusion of ~70 nights of consecutive observations at Las Campanas Observatory to complete the APOGEE-2S observing program after interruptions due to the COVID19 pandemic. Image courtesy of A. Almeida.
Team photo at the Operational Readiness Review and 2014 Team Meeting in Mexico City.