ASPCAP: The Apogee Stellar Parameter and Chemical Abundances Pipeline

TL;DR

ASPCAP is an automated pipeline that analyzes APOGEE stellar spectra to determine atmospheric parameters and chemical abundances, enabling large-scale galactic studies with high precision.

Contribution

This paper details the ASPCAP software, its components, and performance, providing a robust method for analyzing high-resolution stellar spectra in large surveys.

Findings

Achieves 2% accuracy in effective temperature estimation

Provides chemical abundances for up to 15 elements with <0.1 dex precision

Successfully processes over 150,000 stars in SDSS DR12

Abstract

The Apache Point Observatory Galactic Evolution Experiment (APOGEE) has built the largest moderately high-resolution (R=22, 500) spectroscopic map of the stars across the Milky Way, and including dust-obscured areas. The APOGEE Stellar Parameter and Chemical Abundances Pipeline (ASPCAP) is the software developed for the automated analysis of these spectra. ASPCAP determines atmospheric parameters and chemical abundances from observed spectra by comparing observed spectra to libraries of theoretical spectra, using chi-2 minimization in a multidimensional parameter space. The package consists of a fortran90 code that does the actual minimization, and a wrapper IDL code for book-keeping and data handling. This paper explains in detail the ASPCAP components and functionality, and presents results from a number of tests designed to check its performance. ASPCAP provides stellar effective temperatures, surface gravities, and metallicities precise to 2%, 0.1 dex, and 0.05 dex, respectively, for most APOGEE stars, which are predominantly giants. It also provides abundances for up to 15 chemical elements with various levels of precision, typically under 0.1 dex. The final data release (DR12) of the Sloan Digital Sky Survey III contains an APOGEE database of more than 150,000 stars. ASPCAP development continues in the SDSS-IV APOGEE-2 survey.