# Ways to Access APOGEE Data

This page provides a summary of the available outputs from the different stages of the APOGEE pipelines. These can be obtained via a number of tools.

We provide three primary tools to access the APOGEE data: the Catalog Archive Server (CAS), the Science Archive Webapp (SAW), and the Science Archive Server (SAS). File formats are described in the data model and we provide some examples for how to use these resources. 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. Users should consult the "Using APOGEE Data" pages for further instructions on how to properly use and analyze the APOGEE data.

Tool Description Quick Links for APOGEE
Catalog Archive Server
(CAS)
The CAS contains the information from the summary catalogs in a queryable database structure that can be accessed through the SkyServer or directly via SQL.
Science Archive Webapp
(SAW)
The SAW contains spectra and associated parameters in a searchable interactive interface.
Science Archive Server
(SAS)
The SAS houses parameter summary catalogs, spectra, and all intermediate data products in flat files within a directory structure.

## Catalog Archive Server (CAS)

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

The SkyServer Explore tool provides a quick way to find APOGEE spectra for the desired object. The QuickLook pane shows an image and spectrum for each SDSS object. 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, while also providing links to additional 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, velocity, and other constraints from spectroscopic and/or photometric parameters. 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.

We provide some use-cases for the CAS tools on Examples.

## Science Archive Webapp (SAW)

The Science Archive Webapp (SAW) provides a searchable interface for infrared spectra and includes both an interactive view of the spectra and a data download facility (supports both rsync and wget):

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.

We provide some use-cases for the SAW tools on Examples.

The entire spectroscopic dataset, at each stage of its data processing, is available through the SAS. In the subsections to follow, we explain how to find these different data stages in the SAS.

### Summary Catalogs

The tables below give the summary catalog files in FITS format on the SAS. These are found in the following directory: /sas/dr16/apogee/spectro/aspcap/r12/l33

Summary Catalogs
Contents File Name & Direct Link Data Model
summative catalog containing all quantities for each combined spectrum allStar-r12-l33.fits (3.2 Gb) Data Model
"lite" summative catalog containing all quantities for each combined spectrum allStarLite-r12-l33.fits (891 Mb) Data Model
summative catalog containing quantities derived from each individual visit spectrum allVisit-r12.l33.fits (1.6 Gb) Data Model
catalog of Cannon stellar parameters and abundances Not produced in DR16;
Please see DR15 Data Access Documentation for details on how to retrieve these files.
DR15 Cannon Data Model

### Spectral Data

#### Combined ASPCAP Spectrum:: aspcapStar

The pseudo-continuum normalized, combined spectrum, with best matching synthetic ASPCAP spectrum is recorded as one file per object in the aspcapStar file (data model). These are sorted by telescope and field, and can be found in the SAS using a path constructed as follows:

/sas/dr16/apogee/spectro/aspcap/r12/l33/TELESCOPE/FIELD/

The file name is constructed as:

aspcapStar-r12-APOGEE_ID.fits

Where TELESCOPE, FIELD and APOGEE_ID are tags for each object that can be found in the allStar (or equivalent) summary file. Thus, to acquire this file, the user can build the URL from information in the allStar file.

#### Combined Spectrum:: apStar or asStar

The combined, RV-corrected spectra are recorded as one file per object in the apStar or asStar files, where apStar files are created for objects observed by the northern spectrograph and asStar files are created for objects observed by the southern spectrograph. These are sorted by telescope and field, and can be found in the SAS using a path constructed as follows:

 /sas/dr16/apogee/spectro/redux/r12/stars/TELESCOPE/FIELD

The filename is constructed as:

 apStar-r12-APOGEE_ID.fits, asStar-r12-APOGEE_ID.fits

In the allStar (or equivalent) summary file, the filename for the combined spectrum is contained in the FILE tag. Thus, the user can build the URL from information contained in the allStar file.

#### Visit Spectrum:: apVisit or asVisit

The individual visit spectra are recorded as one file per visit in the apVisit or asVisit files. These are sorted by telescope, plate, MJD, and FIBERID. These files can be found in the SAS using a path constructed as follows:

 /sas/dr16/apogee/spectro/redux/r12/visit/TELESCOPE/FIELD/PLATE/MJD

The filename is constructed as:

 apVisit-r12-PLATE-MJD-FIBERID.fits or asVisit-r12-PLATE-MJD-FIBERID.fits

This information can be acquired from the allVisit summary file, or in the VISITS tag of the allStar file. The VISITS tag contains a comma-separated list of the visit file names (without .fits appended).

#### Summary Table for Spectral Data

APOGEE File Name Contents SAS Path Data Model
aspcapStar Pseudo-continuum normalized, combined spectrum, with best matching synthetic ASPCAP spectrum, one file per object /sas/dr16/apogee/spectro/aspcap/r12/l33/TELESCOPE/FIELD/aspcapStar-r12-APOGEE_ID.fits Data Model
apStar
-or-
asStar
Combined spectrum, one file per object /sas/dr16/apogee/spectro/redux/r12/stars/TELESCOPE/FIELD/FILE Data Model
apVisit
-or-
asVisit
Individual visit spectrum, one file per visit /sas/dr16/apogee/spectro/redux/r12/visit/TELESCOPE/FIELD/PLATE/MJD/filename Data Model

### Intermediate Data Products

In addition to the summary catalogs and spectral data, all intermediate data products are also provided in the data release. Here the process is presented in the order of operations from targeting to final ASPCAP parameters and abundances. The pipeline code is available on github: sdss/apogee.

#### Targeting Field Summary Files

DR16 includes four types of files containing useful information on the stars (both targeted and non-targeted) in APOGEE fields and on the fields themselves, the designs, and the plates in which the targets are organized (see further details on this organizational structure in Zasowski et al. 2013 and Zasowski et al. 2017 ).

All summary files can be found in this directory:  /sas/dr16/apogee/target/

Targeting Field Summary Files
Summary File Description Data Model
apogee2Field
-or-
apogeeField
Summary file that contains information for all fields, such as central coordinates Data Model
apogee2Design
-or-
apogeeDesign
contains information on the individual designs, or groups of stars, like color limits and cohort fiber allocations Data Model
apogee2Plate
-or-
apogeePlate
contains information on the physical plates, such as drill angle Data Model

In addition to these summary files, we also have the targeting input files that are used to design each plate. These are organized by survey and by field. They are contained in folders within /sas/dr16/apogee/target/ and the links provided below go to the proper sub-directory.

Targeting Input Files
Field File Description Data Model
apogee2Object contains photometric and proper motion information on the candidate targets in the APOGEE-2 fields; one file for each field in the survey. Data Model
apogeeObject contains photometric and proper motion information on the candidate targets in the APOGEE-1 fields; one file for each field in the survey. Data Model
apogee1mObject contains photometric and proper motion information on the candidate targets in the APOGEE 1m fields; one file for each field in the survey. Similar to apogeeObject
##### Observation Files

APOGEE raw image data are also available on the SAS. These are organized by telescope and MJD. To find these files, the user needs to have acquired the MJD for each visit in the allVisit file.

Files Generated during Data Collection
TELESCOPE Telescope Location of Files
apo25m Apache Point Observatory
2.5 meter
apogee/spectro/data/MJD
lco25m Las Campanas Observatory
2.5 meter
apogee/spectro/data2s/MJD
apo1m Apache Point Observatory
1.0 meter
apogee/spectro/data1m/MJD

The raw data files are named apR-CHIP-EXPOSURE.apz for data taken by the northern spectrograph and asR-CHIP-EXPOSURE.apz for data taken by the southern spectrograph. The CHIP can be “a”, “b”, or “c”, where these letters correspond to the “red”, “green”, and “blue” APOGEE detectors, respectively.
The intermediate-level ap2D and ap1D files are available, but users should consult the data models (ap1D and ap2D), as well as the APOGEE reduction paper (Nidever et al. 2015) before using these files.

##### Visit Level Processing

The visit-level processing occurs in a code called apred and is described on Visit Reduction. These are are organized by telescope, FIELD, PLATE, and MJD. The file path is constructed as follows:

 /sas/dr16/apogee/spectro/redux/r12/visit/TELESCOPE/FIELD/PLATE/MJD/
Files used or created by apred for Visit Processing
File input or output File Description Data Model
apPlan
-or-
asPlan
input the apred processing plan Data Model
apCFrame
-or-
asCFrame
output calibrated spectra file for each chip of each exposure Data Model
apPlate
-or-
asPlate
output Summary file for all exposures of each chip containing the 300 combined flux- and wavelength-calibrated spectra Data Model
apPlateSum
-or-
asPlateSum
output Summary file with metadata for the objects with apPlate/asPlate files
apVisit
-or-
asVisit
output for a given object on a given plate/MJD the combined flux- and wavelength-calibrated spectra for all exposures Data Model
apVisitSum output Summary file with the derived parameters for objects with apVisit/asVisit files (no spectra)
##### Combined Spectra

The visit spectra for each target are combined as described on the visit combination page. This occurs in the following directory:

 /sas/dr16/apogee/spectro/redux/r12/stars/TELESCOPE/FIELD
Files Created for Visit Combination
File input or output File Description Data Model
apStar
-or-
asStar
output Combined spectrum for an individual object. Data Model
apStarLSF output one for each object Data Model
apField
-or-
asField
output Radial velocities and target information for all stars in a given field Data Model
apFieldVisits output Table of individual visit RVs for a given field Data Model
##### APOGEE Stellar Parameters and Chemical Abundances Pipeline (ASPCAP)

The ASPCAP stellar parameters pipeline produces one intermediate file for each field that is then merged to form the allStar summary file. These “aspcapField” files are found in the aspcap directories sorted by telescope and field.

 /sas/dr16/apogee/spectro/aspcap/r12/l33/TELESCOPE/FIELD/aspcapField-FIELD.fits
Files created by ASPCAP
File input or output File Description Data Model
aspcapField output ASPCAP stellar parameters (logg, Teff, [M/H], etc.), normalized spectrum, and best fit spectrum for each stars in a given field. Data Model

The following Value Added Catalogs (VACs) have been produced for the DR16 datasets.

• VAC0045: Open Clusters -- Provides membership probabilities for stars in the vicinity of open clusters targeted in APOGEE-2 and the bulk cluster properties from high-likelihood cluster members.
• VAC0048: Joker -- Provides stellar orbital parameters from multi-epoch RV measurements for binary star candidates.
• VAC0055: StarHorse -- Provides distances and extinctions using spectro-photometry for all stars in DR16.
• VAC0061: AstroNN -- Provides stellar parameters, elemental abundances, distances, and ages from a neural network-based code and orbital parameters for DR16 stars.
• VAC0062: Red Clump -- Provides a catalog of red clump stars using spectro-photometric selections.

The DR16 release involved a major reorganization of the SAS file structure for APOGEE data. For consistency with previous data releases, we provide the equivalent pipeline versions here. Users wishing to access data from data releases are advised to refer to those pages, e.g., DR15 Data Access.

DR16 Pipeline Versions
APOGEE tags each stage of its pipeline with specific version numbers that are then included in the file names and as tags in the allStar (or equivalent) summary file. DR16 uses the following reduction/configuration versions:

• APRED_VERSION:: r12
• APSTAR_VERSION:: stars
• ASPCAP_VERSION:: l33
• RESULTS_VERSION:: l33