APOGEE Data Access
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
Reduction Version Numbers
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-DR14
- 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.
APOGEE DR15 uses the following reduction/configuration versions:
- APRED_VERS
- r8
- APSTAR_VERS-DR14
- 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.
| 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.
| 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-DR14/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-DR14/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-DR14/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-DR14/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
| 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-DR14, ASPCAP_VERS, RESULTS_VERS, LOCATION_ID |
The Cannon Parameters and Abundances Pipeline
The Cannon pipeline involves a number of intermediate files.
| 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-DR14, 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-DR14, 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-DR14, 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).
| 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-DR14, 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-DR14, 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-DR14, LOCATION_ID |
Visit Processing
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.
| 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!
| 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 |
