APOGEE Survey and Instruments Overview
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
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 Spectral Data
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.
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):
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.
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.
- 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.