SDSS-III Infrared Spectroscopic Data from APOGEE

Data Release 10 is the first spectroscopic release from the Apache Point Observatory Galactic Evolution Experiment (APOGEE), including spectra and derived stellar parameters for more than 50,000 stars. APOGEE is an ongoing survey of ~100,000 stars accessing all parts of the Milky Way. By operating in the infrared (H-band) portion of the electromagnetic spectrum, APOGEE is better able to detect light from stars lying in dusty regions of the Milky Way than surveys conducted in the optical, making this survey particularly well-suited for exploring the Galactic disk and bulge. APOGEE's high resolution spectra provide detailed information about the stellar atmospheres; DR10 provides derived effective temperatures, surface gravities, overall metallicities, and information on the abundances of several chemical elements.

DR10 Scope and Status

The APOGEE survey started in Fall 2011 and will run until Summer 2014. By design, spectra for most of the survey stars are integrated over multiple visits spanning at least one month of time to make possible the identification of binary stars through detection of radial velocity variations. In DR10, data for all stars observed during the first year are released, including stars for which more visits are scheduled for subsequent years of the survey. In general, the S/N for those spectra in DR10 is lower than survey specifications, which will be met after all planned visits are executed.

Index map showing locations of fields for which there are data in DR10. Note that different fields have been visited different numbers of times, and not all fields have been completed.

Broadly speaking, the main APOGEE data products released in DR10 are the outputs of two software pipelines. The first one, the data reduction pipeline, delivers extracted, 1-dimensional, calibrated spectra as well as derived radial velocity information. Those interested in working with APOGEE spectra should be aware of instrumental and reduction-specific features visible in the data. Users of the released spectra are strongly advised to visit the Using APOGEE spectra page, and are encouraged to contact us should they find any undocumented issues with the data.

The second pipeline is the APOGEE Stellar Parameters and Chemical Abundances Pipeline (ASPCAP), which aims at achieving the unprecedented feat of determining stellar parameters and 15 elemental abundances through the automatic analysis of APOGEE's high-resolution H-band spectra. This is a very challenging problem, and one that we certainly have not fully solved yet. Currently, ASPCAP delivers derived effective temperatures (T_eff), gravities (log g), metallicities ([M/H]), and chemical abundance ratios [α/M], [C/M], and [N/M]. Users interested in working with those data are *strongly advised* to read the documentation in the Using APOGEE stellar parameters page, where uncertainties, potential systematic effects, and other important issues are discussed.

Quick Look: APOGEE Data

A quick way to view infrared spectroscopic data from APOGEE is via the SkyServer Quick Look tool. Quick Look shows an image and spectrum for all sky objects for which the SDSS has measured a spectrum. The tool also shows the object's radial velocity and derived stellar atmospheric parameters, and gives links to further data, including the spectrum as a FITS file.

The SDSS SkyServer quick look tool shows an image and spectrum of any survey star, with links to further data

Quick Look view of some APOGEE star. Click on the image to go to the Quick Look tool

Catalog Data

All APOGEE catalog data are available through the search tools of SkyServer. The Spectroscopic Query Form lets you search for spectroscopic catalog objects by position, catalog name, and several stellar parameters. SQL Search lets you create your own search; see the SkyServer SQL Tutorial to learn how to write SQL queries. An even more flexible and powerful interface is CasJobs, which allows you to save and analyze all of your search results.

Spectra (FITS)

In addition to the APOGEE catalog data, SDSS also makes all the APOGEE spectra available as FITS files through the Science Archive Server, which can return FITS spectra either individually or in bulk.

Information About APOGEE Data

Additional pages describe how to understand and use APOGEE data. Use the links below (echoed on the left sidebar menu on each page) to learn more.

Understanding the APOGEE survey gives an overview of how APOGEE spectroscopic data are taken and organized.
Available data describes in detail what APOGEE data products are available through the Science Archive Server and SkyServer.
Using APOGEE spectra describes some important features in APOGEE spectra about which anyone looking at spectra should be aware.
Using APOGEE stellar parameters describes important things you need to know if you plan to use the derived stellar atmospheric parameters.
Database catalogs describes the APOGEE information that is stored within the CAS database and summary data files and how it can be used. This includes some examples of how to query the database or summary data files to select out different pieces of information for different types of targets.
Several pages describe the steps in the APOGEE software pipelines, and the files created at each step:
- Target selection describes the way in which APOGEE targets are chosen (targeted), and how this is documented in the target flags.
- Visit reduction gives information about how individual visit spectra are observed, processed and stored.
- Combined spectra gives information about how the combined spectra for each star are created and stored, including information about the derivation of radial velocities.
- Derivation of stellar parameters describes how the stellar parameters available in APOGEE spectroscopic catalogs (which include effective temperature, surface gravity, heavy element abundance [metals/H], alpha-element abundance [α/M], carbon abundance [C/M], and nitrogen abundance [N/M]) are derived.
Caveats is a running list of known issues with the DR10 release.