APOGEE Survey and Instruments Overview

Apache Point Observatory Galactic Evolution Experiment (APOGEE)

APOGEE collects near-infrared spectra in order to carry out a systematic survey of all Milky Way Components using simple selection criteria.

The APOGEE Survey

APOGEE is a large-scale, stellar spectroscopic survey conducted in the near-infrared portion of the electromagnetic spectrum (H-band, details of wavelength coverage). As opposed to optical wavelength surveys, APOGEE can more easily detect light from stars situated in the dusty regions of the Milky Way, such as the disk and bulge. The high-resolution APOGEE spectra (R~22500) provide detailed chemical and kinematic information for target stars.

The first installment of the APOGEE Survey (APOGEE-1) was executed over three period, from September 2011 to July 2014. Observations were performed with the APOGEE-North spectrograph on the Sloan Foundation 2.5m Telescope of Apache Point Observatory (APO). The second installment, APOGEE-2, will be carried out from July 2014 through Summer 2020 and continues data acquisition at APO. in addition, observations will be taken with the APOGEE-South spectrograph on the Irénée du Pont 2.5m Telescope of Las Campanas Observatory (LCO).

For both APOGEE instruments, 300 spectra of science and calibration targets are acquired simultaneously.

By design, spectra for most of the survey stars are integrated over multiple visits, with at least one visit separated by at least one month, to enable the identification of binary stars through detection of radial velocity variations. For most survey fields, multiple observations are made at different epochs to allow for the identification of binary stars through detection of their radial velocity variations. Combined spectra of these multiple observations are one of APOGEE’s primary data products. Stellar atmospheric parameters and chemical abundances are derived from these combined spectra using the APOGEE Stellar Parameters and Chemical Abundances Pipeline (ASPCAP).

This page provides a brief introduction to the APOGEE survey and its data. See the APOGEE technical papers for detailed information on all aspects of the APOGEE survey in a format that you can cite in your work.

APOGEE Instruments

Since July 2014, APOGEE-2N data collection has been taken with the 2.5-m Sloan Foundation Telescope at Apache Point Observatory. APOGEE-2S, beginning February 2017, has conducted observations with the 2.5-m Irenee du Pont Telescope at Las Campanas Observatory.

APOGEE Spectral Data

Prior to Data Release 10, all released SDSS spectroscopic data, including the stellar data from the SEGUE and SEGUE-2 surveys, were taken with optical spectrographs.

APOGEE spectra sample the infrared portion of the electromagnetic spectrum, covering a wavelength range of 1.5-1.7 microns (i.e., H-band; see details of wavelength coverage). Moreover, the spectra are taken at relatively high spectral resolution — 10 times higher than the SDSS optical spectra. This higher resolution enables a more detailed look at the light emitted by stars, and allows the radial velocities, chemical compositions, and physical properties of the survey stars to be measured with greater precision and accuracy. The APOGEE spectra and associated products were first released in DR10. For more information on the related instrumentation, see the detailed description of the APOGEE spectrograph.

Data Access

Several interfaces are available to access the data (see APOGEE Data Access for more details):

Catalog Archive Server (CAS)

APOGEE target information and derived radial velocities, stellar parameters, and abundances are loaded into the Catalog Archive Server (CAS) database.  This contains a number of ways of interfacing with the database, including low-level SQL access through the CasJobs interface that allows you to save and analyze all your search results.

Science Archive Server (SAS)

Summary FITS files containing the derived radial velocities, stellar parameters, and abundances for all APOGEE stars, as well as all raw and processed APOGEE data are available from the APOGEE Science Archive Server (SAS), including all directories and files listed in the Data Model.
The Science Archive Webapp provides a searchable interface for infrared spectra, and includes an interactive view of infrared spectra, and a data download facility (supports both rsync and wget):

SkyServer

The SkyServer Explore tool provides a quick way to find APOGEE spectra for a desired object. Quick Look shows an image and spectrum for all SDSS objects. For objects with APOGEE spectra, the tool includes an APOGEE section. The APOGEE section of the Explore tool shows a composite spectrum, radial velocities, and derived stellar atmospheric parameters, and gives links to further data, including the spectrum as a FITS file.

All APOGEE catalog data are available through the search tools of SkyServer. The Infrared Spectroscopy Query Form lets you search for APOGEE catalog objects by position, spectral classification, redshift, and other constraints in spectroscopy and/or imaging. SQL Search lets you create your own search using the SQL database programming language; see the SkyServer SQL Tutorial to learn how to write SQL queries.

Additional Information

Broadly speaking, the main APOGEE data products released in DR14 are the outputs of two software pipelines. The data reduction pipeline delivers extracted, one-dimensional, calibrated spectra as well as derived radial velocity information. Those interested in working with APOGEE spectra should be aware of instrumental and reduction-specific features visible in the data. Users of the released spectra are strongly advised to visit the Using APOGEE Spectra page.

The APOGEE Stellar Parameters and Chemical Abundances Pipeline (ASPCAP) determines stellar parameters and abundances through the automatic analysis of APOGEE’s high-resolution H-band spectra. ASPCAP delivers derived effective temperatures (Teff), surface gravities (log g), and 20 chemical species. Users interested in working with ASPCAP data are strongly advised to read the documentation in the Using APOGEE Stellar Parameters page and the Using APOGEE Chemical Abundances page, where uncertainties, potential systematic effects, and other important issues are discussed.

Detailed APOGEE Information

The following pages give detailed information about various aspects of APOGEE.

The APOGEE Instrument and Survey
gives an overview of how APOGEE spectroscopic data are taken and organized.
Examples
provides examples of how to query the database or summary data files in order to retrieve a variety of information for different types of targets.
APOGEE Data Access
describes all of the APOGEE data products that are available through the Science Archive Server.
Using APOGEE Stellar Parameters
describes important things you need to know if you plan to use the derived stellar atmospheric parameters.
Using APOGEE Chemical Abundances
describes important things you need to know if you plan to use the derived elemental abundances.
Using APOGEE Spectra
describes some important features in APOGEE spectra about which anyone looking at spectra should be aware.

APOGEE Software Pipelines and Associated Steps

The following pages describe the steps in the APOGEE software pipelines, and the files created at each step.

APOGEE Target Information
describes the way in which APOGEE targets are chosen (targeted), and how this is documented in the target flags.
APOGEE Visit Spectra Reduction
gives information about how individual visit spectra are observed, processed and stored.
APOGEE Visit Spectra Combination
gives information about how the combined spectra for each star are created and stored, including information about the derivation of radial velocities.
APOGEE Stellar Parameter and Abundance Determination
describes how the stellar parameters and abundances available in APOGEE spectroscopic catalogs are derived.
APOGEE Caveats
gives a running list of known issues with the DR14 release.