APOGEE Data Access


This page provides a summary of the files associated with the different steps of the APOGEE reduction pipeline. These tables include links to the file format documentation (the “data model”) and templates that can be used to generate Science Archive Server (SAS) URLs for those files.

Most of the catalog data (but not the spectra themselves) have been loaded into the Catalog Archive Server (CAS) database. Users may be better off obtaining SDSS data through a CAS query than they are downloading the data files from the SAS. Simple queries can be used to select just the objects and parameters of interest, while more complex queries can be used to do complex calculations on many objects, thereby avoiding the need to download the data on them at all.

The major spectroscopic results are contained in a few different file structures (on SAS) and database tables (in CAS), listed below. Note that the links into SAS below bring you into the full directory tree; before perusing that, it may be best to read both Understanding APOGEE Spectroscopic Data and the data model.

APOGEE Pipeline Reduction Steps
This page describes APOGEE data products. Detailed descriptions of the APOGEE pipeline reduction steps are provided on these pages:

Use of APOGEE Data Products
Additional descriptions pertaining to the use of the resulting data products can be found on additional pages:

Reduction Version Numbers

APOGEE Version Conventions

The APOGEE pipeline is continually being improved, so it may be important to track the version of the pipeline that was used to reduce APOGEE spectra. To allow for changes in different sections of the pipeline without requiring all data to be rerun through all sections of the code again, four separate version names track the software/configuration used in different portions of the pipeline:

denotes the version of the basic spectra reduction used to generate the visit spectra.
denotes the version of the code used to combine individual visit spectra into higher signal-to-noise, resampled, combined spectra.
denotes the version of the code used to determine the stellar atmospheric parameters for each combined spectrum.
denotes the version of the code used to (1) compile the final results, and (2) apply additional empirical corrections and set data quality flags based on evaluation of results for calibration objects. A given RESULTS_VERS implies versions of all of the preceding steps, and thus uniquely identifies the full set of software used.

DR12 Versions

APOGEE DR12 uses the following reduction/configuration versions:


Catalogs of Quantities Measured from APOGEE Spectra

Summary FITS table files of cataloged parameters (as distinct from the spectra themselves) are provided in the SAS. These catalog files are also loaded into the CAS to enable database access. Note that one of the FITS table files (allStar) is split into two separate CAS tables: aspcapStar and apogeeStar, and thus listed twice in the table below.

Spectra catalogs
description SAS location CAS table
catalog of ASPCAP parameters for observed stars allStar-RESULTS_VERS.fits
(in APOGEE_REDUX; see datamodel)
catalog of stellar parameters from combined spectra
(e.g., RVs)
(in APOGEE_REDUX; see datamodel)
catalog of parameters from individual visit spectra allVisit-RESULTS_VERS.fits
(in APOGEE_REDUX; see datamodel)

Spectral Data

Spectral data are available in the SAS. Three different types of reduced spectra are available: visit spectra, combined spectra, and ASPCAP spectra. Visit spectra give spectra of individual visits and are organized by PLATE and MJD. Combined spectra (all visits combined) and ASPCAP spectra (pseudocontinuum-normalized combined spectra) are organized by field (encoded by a LOCATION_ID).

One way to associate PLATES, LOCATION_ID, and field names is to look at the index embedded in the SAS. You can also get this information from the CAS or the summary data files, see, e.g., examples for plates or for location IDs.

To access APOGEE spectra, see the SAS webapp . This allows you to do some simple searches on objects and interactively plot the spectra. It can also be used to construct lists of small or large numbers of spectra to be downloaded in bulk, see Bulk Data Downloads.

APOGEE Spectra themselves

Description SAS location SAS interface
Pseudo-continuum normalized, combined spectra, with best matching synthetic spectrum, one file per object aspcapStar-RESULTS_VERS-STARNAME.fits
Combined spectra, one file per object apStar-APSTAR_VERS-STARNAME.fits
Individual spectra, one file per PLATE-MJD-FIBER apVisit-APRED_VERS-PLATE-MJD-FIBER.fits

Intermediate Data Products

While most users are likely to be satisfied with the data in the files listed above, there are a number of lower level intermediate processed files, which we list here. The templates are in “C printf ” format, and can be used in C, bash, Python, and many other languages to automatically generate URLs.

APOGEE Raw Data Collection

APOGEE raw data are stored on the SAS. It is probably unlikely that users will want to access these, because the raw data contain all of the up-the-ramp detector reads (every 10s) for every exposure; it’s a lot of data!

SAS Files Generated in Spectroscopic Data Collection
file type in/out Description URL format format parameters
log file out records exposures collected on a night not public
apR out raw spectroscopic data frames $APOGEE_DATA/%d/apR-%c-%08d.apz mjd, detector (a,b,or c), exposure id
plPlugMapM in records which fiber corresponds to which hole in a plate (and therefore to which objects, and to what coordinates on the sky) not public

APOGEE Visit Processing

For details about the processing of the visit data, see the Visit Reduction page and/or the APOGEE data reduction paper (Nidever et al., in prep).

The apred pipeline reads science and calibration exposures from the spectrographs, collapses these data cubes into two dimensional exposures, reduces and calibrates the science exposures, extracts the one dimensional spectra from the two dimensional exposures, corrects for sky emission and telluric absorption, stacks multiple dithered exposures into well-sampled spectra, and produces corresponding masks and noise estimates.

SAS Files Used or Generated by the apred Pipeline
file type in/out description URL format format parameters
apPlan in the apred processing plan $APOGEE_REDUX/$APRED_VERS/apo25m/%d/%05d/apPlan-%04d-%05d.par plate, mjd, plate, mjd
apCframe out calibrated spectra for a single CCD and exposure $APOGEE_REDUX/$APRED_VERS/apo25m/%04d/%05d/apCframe-%c-%08d.par plate, mjd, chip (a, b, or c), exposure id
apPlate out the 300 combined flux- and wavelength-calibrated spectra over all exposures (potentially spanning multiple nights) for a given mapped plate $APOGEE_REDUX/$APRED_VERS/apo25m/%s/%04d/apPlate-%04d-%05d.fits plate, mjd, plate, mjd
apVisit out the combined flux- and wavelength-calibrated spectra over all exposures (potentially spanning multiple nights) for a given object on a given plate/MJD $APOGEE_REDUX/$APRED_VERS/apo25m/%s/%04d/apVisit-%04d-%05d-%03d.fits plate, mjd, plate, mjd

Stellar Combination Processing (apstar)

For details about the process, see the page on visit combination and/or the reduction paper (Nidever et al., in prep).

SAS files used or generated by the visit combination pipeline
file type in/out description URL format format parameters
apField out $APOGEE_REDUX/%s/%s/%s/apField-%d.fits APRED_VERS, APSTAR_VERS, LOCATION_ID
apFieldVisits out $APOGEE_REDUX/%s/%s/%s/apFieldVisits-%d.fits APRED_VERS, APSTAR_VERS, LOCATION_ID

APOGEE Stellar Parameters and Chemical Abundances Pipeline (ASPCAP)

The ASPCAP stellar parameters pipeline produces a number of files:

SAS Files Used or Generated by the ASPCAP pipeline
file type in/out description URL format format parameters
aspcapField out ASPCAP stellar parameters (log g, Teff, [M/H], etc.) $APOGEE_REDUX/%s/%s/%s/%s//aspcapField-%04d.fits APRED_VERS, APSTAR_VERS, ASPCAP_VERS, RESULTS_VERS, LOCATION_ID
aspcapStar out ASPCAP stellar parameters $APOGEE_REDUX/%s/%s/%s/%s/LOCATION_ID/aspcapStar-%s-%04d.fits APRED_VERS, APSTAR_VERS, ASPCAP_VERS, RESULTS_VERS, RESULTS_VERS, LOCATION_ID