APOGEE Data Releases 13 and 14: Stellar Parameter and Abundance Comparisons With Independent Analyses

TL;DR

This paper presents the APOGEE Data Releases 13 and 14, detailing the spectra, stellar parameters, and abundances, and evaluates the accuracy of the ASPCAP pipeline through comparisons with independent optical analyses.

Contribution

It provides a comprehensive comparison of APOGEE stellar parameters and abundances with independent optical analyses, validating the pipeline’s accuracy and systematic differences.

Findings

Most elemental abundances differ by less than 0.05 dex from independent analyses.

Magnesium shows the most accurate alpha-element measurement and disk separation.

Nickel is the most accurate iron-peak element besides iron.

Abstract

Data from the SDSS-IV / Apache Point Observatory Galactic Evolution Experiment (APOGEE-2) have been released as part of SDSS Data Releases 13 (DR13) and 14 (DR14). These include high resolution H-band spectra, radial velocities, and derived stellar parameters and abundances. DR13, released in August 2016, contained APOGEE data for roughly 150,000 stars, and DR14, released in August 2017, added about 110,000 more. Stellar parameters and abundances have been derived with an automated pipeline, the APOGEE Stellar Parameter and Chemical Abundance Pipeline (ASPCAP). We evaluate the performance of this pipeline by comparing the derived stellar parameters and abundances to those inferred from optical spectra and analysis for several hundred stars. For most elements -- C, Na, Mg, Al, Si, S, Ca, Cr, Mn, Ni -- the DR14 ASPCAP analysis have systematic differences with the comparisons samples of less than 0.05 dex (median), and random differences of less than 0.15 dex (standard deviation). These differences are a combination of the uncertainties in both the comparison samples as well as the ASPCAP-analysis. Compared to the references, magnesium is the most accurate alpha-element derived by ASPCAP, and shows a very clear thin/thick disk separation, while nickel is the most accurate iron-peak element (besides iron).