# APOGEE Data Access

Note that the APOGEE data in DR15 are identical to those in DR14, but use the DR15 documentation pages for reference.

## Introduction

This page provides a summary of the available outputs from the different stages of the APOGEE pipelines. Parameters derived from APOGEE spectra (radial velocities, stellar atmospheric parameters, and element abundances), as well as the spectra themselves, are stored in files and database tables that are available from different SDSS data access tools. Here, links are provided as well as advice on how to get the types of data users might need, along with links to the file format documentation (aka, the "data model"). Some examples of querying these resources are available here.

The primary means of accessing APOGEE data are the Science Archive Server (SAS) and the Catalog Archive Server (CAS). The SAS houses spectra and parameter summary catalogs in flat files (often FITS format) within a directory structure. The CAS contains the information in the summary catalogs in a queryable database structure.

The entire spectroscopic dataset, at all stages of reduction, is available through the SAS, generally in the form of FITS files. However, many users will be satisfied with the final allStar catalog on the SAS, which gives radial velocities, stellar parameters, and abundances for each star, obtained from the combined spectra. For users interested in radial velocity (RV) variations, the SAS also contains a separate allVisit catalog, which gives information and RVs for each individual visit.

Most of the catalog data (but not the spectra themselves) have also been loaded into the CAS database. For users who prefer a database interface (SQL), the CAS provides an effective alternative (or at least an informative precursor) to navigating the SAS's directories and downloading the full data files. 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, perhaps even avoiding the need to download the data at all.

## Background Information and File Naming Conventions

APOGEE Pipeline Steps
Detailed descriptions of the APOGEE pipelines' steps are provided on these pages:

Use of APOGEE Data Products
Descriptions relevant to the use of the resulting data products can be found on these pages:

### Reduction Version Numbers

APOGEE Pipeline Version

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

APRED_VERS
denotes the version of the basic reduction used to generate the visit spectra.
APSTAR_VERS
denotes the version of the code used to combine individual visit spectra into single combined spectra.
ASPCAP_VERS
denotes the version of the code used to determine the ASPCAP stellar atmospheric parameters for each combined spectrum.
RESULTS_VERS
denotes the version of the code used to compile the final results, apply empirical corrections, and set data quality flags based on evaluation of results for calibration objects.
CANNON_VERS
denotes the version of the code used to determine the Cannon stellar atmospheric parameters for each combined spectrum.

Note that a given RESULTS_VERS implies versions of all of the preceding steps, and thus uniquely identifies the full set of software used.

DR15 Versions

APOGEE DR15 uses the following reduction/configuration versions:

APRED_VERS
r8
APSTAR_VERS
stars
ASPCAP_VERS
l31c
RESULTS_VERS
l31c.2
CANNON_VERS
cannon

## APOGEE Data

The sections below provide names and brief descriptions of the SAS files and CAS tables relevant to different flavors of APOGEE data. These include summary catalogs of final parameters and abundances, reduced spectra and their best-fit synthetic models, and raw and intermediate data reduction products. Further essential details about this content are found in Using APOGEE Spectra, Using APOGEE Parameters, and Using APOGEE Abundances.

### Summary Catalogs

The tables below gives the main summary files in FITS format (on the SAS) and database tables (in CAS). Be aware that the links into the SAS bring you into the full directory tree; before perusing that, it may be helpful to read both Understanding APOGEE Spectroscopic Data and the data model. Note that data in one of the FITS files (allStar) are split between two separate CAS tables: aspcapStar and apogeeStar.

Catalog Data
Contents SAS Location CAS Table
catalog of ASPCAP stellar parameters and abundances allStar-l31c.2.fits
(in APOGEE_REDUX; see datamodel)
aspcapStar
catalog of Cannon stellar parameters and abundances allStarCannon-l31c.2.fits
(in APOGEE_REDUX; see datamodel)
cannonStar
catalog of stellar properties from combined spectra
(e.g., RVs)
allStar-l31c.2.fits
(in APOGEE_REDUX; see datamodel)
apogeeStar
catalog of properties from individual visit spectra allVisit-l31c.2.fits
(in APOGEE_REDUX; see datamodel)
apogeeVisit

The DR15 CAS has several predefined table-based functions that can be used to return all stellar parameters or all chemical abundances from the aspcapStar table, rather than specifying each element separately in a SELECT statement. These include:

dbo.fAspcapParams
returns all parameters (Teff, log g, vmicro, vmacro, vsini, [M/H], [α/M])
dbo.fAspcapElems
returns abundances of all calibrated species.

Uncertainties and flags can also be retrieved by using dbo.fAspcapParamErrs, dbo.fAspcapParamFlags, dbo.fAspcapElemErrs, and dbo.fAspcapElemFlags, and values, uncertainties, and flags can be obtained in single calls to dbo.fAspcapParamsAll and dbo.fAspcapElemsAll. Use of these functions requires a CROSS APPLY statement.

### APOGEE Spectral Data

Spectral data are available only in the SAS. Three different types of reduced spectra are available: visit spectra, combined spectra, and ASPCAP/Cannon spectra. Visit spectra, which come from individual visits to a source, are organized by the PLATE_ID and MJD of the visit. Combined spectra (combination of all visits) and ASPCAP/Cannon spectra (pseudo-continuum normalized combined spectra) are organized by the target's FIELD, which is encoded in a LOCATION_ID.

One way to associate PLATE_ID, LOCATION_ID, and FIELD name is to look at this index embedded in the SAS. You can also get this information from the CAS or the summary data files above. See examples for, e.g., plates or for location IDs.

To access APOGEE spectra, most users will first (or only) employ the Science Archive Webapp (SAW). The SAW permits some simple object searches as well as interactively plots their associated spectra. It can also be used to construct lists of spectra to be downloaded in bulk; see further instructions in Bulk Data Downloads.

Spectral Data

Description SAS Location Science Archive Webapp
Pseudo-continuum normalized, combined spectrum, with best matching synthetic ASPCAP spectrum, one file per object aspcapStar-RESULTS_VERS-STARNAME.fits
(in APOGEE_REDUX/APRED_VERS/APSTAR_VERS/ASPCAP_VERS/RESULTS_VERS/LOCATION_ID; see datamodel)
Spectrum Search
Pseudo-continuum normalized, combined spectrum, with best matching Cannon spectral model, one file per object cannonStar-RESULTS_VERS-STARNAME-xh-censor.fits
(in APOGEE_REDUX/APRED_VERS/APSTAR_VERS/ASPCAP_VERS/RESULTS_VERS/CANNON_VERS/LOCATION_ID; see datamodel)
Spectrum Search
Combined spectrum, one file per object apStar-APSTAR_VERS-STARNAME.fits
(in APOGEE_REDUX/APRED_VERS/APSTAR_VERS/TELESCOPE/LOCATION_ID; see datamodel)
Spectrum Search
Individual visit spectrum, one file per PLATE-FIBER-MJD apVisit-APRED_VERS-PLATE-MJD-FIBER.fits
(in APOGEE_REDUX/APRED_VERS/TELESCOPE/PLATE_ID/MJD5; see datamodel)
Spectrum Search

### 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 are listed here. The templates are in "code>C printf format and can be used in C, bash, Python, and many other languages to automatically generate URLs.

#### APOGEE Stellar Parameters and Chemical Abundances Pipeline (ASPCAP)

The ASPCAP stellar parameters pipeline produces one intermediate file, used to make the aspcapStar file described above.

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.), normalized spectra, and best fit spectra for all stars in a given field APOGEE_REDUX/%s/%s/%s/%s/%s/aspcapField-%04d.fits APRED_VERS, APSTAR_VERS, ASPCAP_VERS, RESULTS_VERS, LOCATION_ID

#### The Cannon Parameters and Abundances Pipeline

The Cannon pipeline involves a number of intermediate files.

SAS Files Used or Generated by the Cannon
file type in/out description URL format format parameters
Cannon model out/in trained model: pixel flux coefficients and covariances APOGEE_REDUX/%s/%s/%s/%s/%s/apogee-dr14-giants-xh-censor.model APRED_VERS, APSTAR_VERS, ASPCAP_VERS, RESULTS_VERS, CANNON_VERS
cannonTrainingSet in set of ASPCAP parameters and abundances used to train the Cannon model APOGEE_REDUX/%s/%s/%s/%s/%s/apogee-dr14-giants-xh-censor-training-set.fits APRED_VERS, APSTAR_VERS, ASPCAP_VERS, RESULTS_VERS, CANNON_VERS
cannonField out Cannon stellar parameters (log g, Teff, [M/H], etc.), normalized spectra, and reconstructed spectra for all stars in a given field APOGEE_REDUX/%s/%s/%s/%s/%s/%s/cannonField-%04d.fits APRED_VERS, APSTAR_VERS, ASPCAP_VERS, RESULTS_VERS, CANNON_VERS, LOCATION_ID

#### Combined Spectra

For details regarding the process of combining visits for the same target see the visit combination page and/or the data reduction and processing paper (Nidever et al. 2015).

SAS Files Used or Generated By the Visit Combination Pipeline
file type in/out description URL format format parameters
apStar out Combined spectrum for an individual star APOGEE_REDUX/%s/%s/%s/apStar-%s.fits APRED_VERS, APSTAR_VERS, LOCATION_ID, APOGEE_ID
apField out Radial velocities, target information for all stars in a given field APOGEE_REDUX/%s/%s/%s/apField-%d.fits APRED_VERS, APSTAR_VERS, LOCATION_ID
apFieldVisits out Table of individual visit RVs for a given field APOGEE_REDUX/%s/%s/%s/apFieldVisits-%d.fits APRED_VERS, APSTAR_VERS, LOCATION_ID

#### Visit Processing

For information about the processing of APOGEE visit data, see the Visit Reduction page and the APOGEE data reduction paper (Nidever et al. 2015).

In short, the apred pipeline (a) reads science and calibration exposures from the spectrographs, (b) collapses these data cubes into two dimensional exposures, (c) reduces and calibrates the science exposures, (d) extracts the one dimensional spectra from the two dimensional exposures, (e) corrects for sky emission and telluric absorption, (f) stacks multiple dithered exposures into well-sampled spectra, and (g) 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

#### Raw Data Collection

APOGEE raw data are stored on the SAS. It is highly 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 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