# APOGEE: Probing the Evolution of the Milky Way

## Apache Point Observatory Galactic Evolution Experiment 1 (APOGEE-1)

### APOGEE-1 at a Glance:

• Bright time observations at Apache Point Observatory
• September 2011 - July 2014
• Instrument: APOGEE-N
• 150,000 stars in the Galactic bulge, disk, and halo
• Spectral Resolution $R \sim 22,500$
• Typical signal-to-noise $\gt 100$
• Wavelength Range: $1.51-1.70 \mu m$
• Velocity uncertainties $\sim 200$ m/s
• Stellar parameters including $\log g$, $T_{eff}$, [Fe/H], [$\alpha$/Fe]
• Abundance of 15 chemical species to 0.1 dex precision

The Apache Point Observatory Galactic Evolution Experiment 1 (APOGEE-1) employed high-resolution, high signal-to-noise infrared spectroscopy to penetrate the dust that obscures significant fractions of the disk and bulge of our Galaxy. APOGEE-1 aimed to survey 100,000 red giant stars across the full range of the Galactic bulge, bar, disk, and halo. At its conclusion, APOGEE-1 observed over 150,000 stars. APOGEE-1 generated precise radial velocities and detailed chemical abundances, providing unprecedented insights into the dynamical structure and chemical history of the Galaxy. In conjunction with the planet-finding surveys, Kepler and CoRoT, APOGEE-1 unraveled problems in fundamental astrophysics.

In SDSS-III, the SEGUE-2 and APOGEE-1 datasets played a central role in near-field cosmology tests of galaxy formation and the small-scale distribution of dark matter.

IR image of the inner Galaxy, showing the plane and bulge of the Galaxy full of stars and dust. APOGEE-1 used near-infrared instrumentation, which is less affected by the extinction from interstellar dust, to study stars within the disk (now continued in APOGEE-2). Image: 2MASS

## APOGEE-1 Dataset

### Accessing APOGEE-1 data

Data Release 17 is the latest public release of APOGEE spectra and includes all data taken in APOGEE-1. The APOGEE-1 data has been processed with pipelines that have been improved throughout the operations of APOGEE-2. The following resources will help users interested in APOGEE-1 data:

Majewski et al. (2017) provides a detailed description of APOGEE-1, including a summary of major scientific results. Wilson et al. (2019) provides a description of the APOGEE-N instrument and hardware.

All APOGEE-1 technical publications are archived with the APOGEE-2 DR17 Technical Publications Repository. APOGEE-1 had data releases in DR10 and DR12.

### The APOGEE-1 Sample:

At the conclusion of APOGEE-1, DR12 included data for ~163,000 targets. The targets were distributed as follows:

• ~15,000 stars toward the Bulge
• ~28,000 stars toward the Halo
• ~55,000 stars toward the Disk
• ~14,000 stars in the Kepler or CoRoT fields
• ~8,000 objects from Ancillary Science programs
• ~1,800 stars toward the Halo Streams
• ~1,200 stars toward the Sagittarius dSph
• ~8,000 stars toward the Star Cluster fields
• ~900 bright stars observed with the NMSU 1m telescope + APOGEE
• ~17,000 hot stars for telluric correction
Final map of observations from APOGEE-1. The individual fields are color-coded by their targeting depth and because all APOGEE-1 observations were designed to have signal-to-noise of $\sim 100$ those fields with longer total integrations reach fainter magnitudes.
Projection of the APOGEE-1 observations onto an artist's impression of the Milky Way. The points are color-coded by their metallicity and shows the overall metallicity gradient in the Milky Way. Image Credit: Majewski et al. (2017)

## Snapshots of the APOGEE-1 Team

Team photo from an APOGEE-1 Team meeting held at Texas Christian University in 2014.
Team photo from APOGEE-1 Team Meeting at the University of Virginia with many of the principal task leaders from early in the project.