The APO-K2 Catalog. I. ∼7500 Red Giants with Fundamental Stellar Parameters from APOGEE DR17 Spectroscopy and K2-GAP Asteroseismology

Jessica Schonhut-Stasik, Joel C. Zinn, Keivan G. Stassun, Marc Pinsonneault, Jennifer A. Johnson, Jack T. Warfield, Dennis Stello, Yvonne Elsworth, Rafael A. García, Savita Mathur, Benoit Mosser, Marc Hon, Jamie Tayar, Guy S. Stringfellow, Rachael L. Beaton, Henrik Jönsson, Dante Minniti

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)


We present a catalog of fundamental stellar properties for ∼7500 evolved stars, including stellar radii and masses, determined from the combination of spectroscopic observations from the Apache Point Observatory Galactic Evolution Experiment, part of the Sloan Digital Sky Survey IV, and asteroseismology from K2. The resulting APO-K2 catalog provides spectroscopically derived temperatures and metallicities, asteroseismic global parameters, evolutionary states, and asteroseismically derived masses and radii. Additionally, we include kinematic information from Gaia. We investigate the multidimensional space of abundance, stellar mass, and velocity with an eye toward applications in Galactic archaeology. The APO-K2 sample has a large population of low-metallicity stars (∼288 with [M/H] ≤ −1), and their asteroseismic masses are larger than astrophysical estimates. We argue that this may reflect offsets in the adopted fundamental temperature scale for metal-poor stars rather than metallicity-dependent issues with interpreting asteroseismic data. We characterize the kinematic properties of the population as a function of α enhancement and position in the disk and identify those stars in the sample that are candidate components of the Gaia-Enceladus merger. Importantly, we characterize the selection function for the APO-K2 sample as a function of metallicity, radius, mass, ν max , color, and magnitude referencing Galactic simulations and target selection criteria to enable robust statistical inferences with the catalog.

Original languageEnglish
Article number50
JournalAstronomical Journal
Issue number2
Publication statusPublished - 1 Feb 2024

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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