Value Added Catalogs

APOGEE red-clump catalog

APOGEE's target selection algorithm includes many red-clump (RC) stars in the APOGEE sample. A new method for identifying red-clump stars from spectrophotometric data and its application to the APOGEE data was presented in Bovy et al. (2014). This technique creates a very pure sample of red-clump stars with minimal contamination from red-giant-branch, secondary-red-clump, and asymptotic-giant-branch stars. The narrowness of the RC locus in color-metallicity-luminosity space allows distances to the stars to be assigned with an accuracy of 5%-10%. The purity is estimated to be about 95%.

The DR12 release includes both the DR11 version of the RC catalog, which was based on the first two years of APOGEE data and was the specific subject of Bovy et al. (2014), and the DR12 version of the catalog, which for all purposes supersedes the DR11 catalog. The DR11 catalog was used by Nidever et al. (2014) to study the distribution of abundances in the Milky Way disk.

The following table lists where the RC catalogs can be found on the SAS, where to find their data model, and some basic information about the catalog.

Accounting for Observational Biases in APOGEE

Section 4 of Bovy et al. (2014) described how to correct for observational biases due to the APOGEE target selection (for the whole (J-Ks)0 > 0.5 sample, not just the red-clump sample). Specifically, these are the biases due to the incomplete sampling of the available targets with (J-Ks)0 > 0.5 as a function of position on the sky and magnitude. Tools to correct for these biases are included in the apogee python package and extensive documentation on how to use this package is given on the package webpage. This selection-function code has been updated for DR12 (from the DR11 version described in the paper).

Section 5 of Bovy et al. (2014) discussed astrophysical biases due to the red-clump selection. Specifically, they investigated the biases in recovering the underlying age and metallicity distribution by only selecting red-clump stars. The RC selection preferentially select stars with ages between 1 and 4 Gyr and with metallicities > -0.9. Please consult section 5 of the paper above for full details. The apogee python package also has tools for working with the astrophysical biases.