Chemical Cartography with APOGEE: Mapping Disk Populations with a 2-process Model and Residual Abundances

David H. Weinberg, Jon A. Holtzman, Jennifer A. Johnson, Christian Hayes, Sten Hasselquist, Matthew Shetrone, Yuan Sen Ting, Rachael L. Beaton, Timothy C. Beers, Jonathan C. Bird, Dmitry Bizyaev, Michael R. Blanton, Katia Cunha, José G. Fernández-Trincado, Peter M. Frinchaboy, D. A. García-Hernández, Emily Griffith, James W. Johnson, Henrik Jönsson, Richard R. LaneHenry W. Leung, J. Ted Mackereth, Steven R. Majewski, Szabolcs Mészáros, Christian Nitschelm, Kaike Pan, Ricardo P. Schiavon, Donald P. Schneider, Mathias Schultheis, Verne Smith, Jennifer S. Sobeck, Keivan G. Stassun, Guy S. Stringfellow, Fiorenzo Vincenzo, John C. Wilson, Gail Zasowski

Research output: Contribution to journalArticlepeer-review

17 Scopus citations


We apply a novel statistical analysis to measurements of 16 elemental abundances in 34,410 Milky Way disk stars from the final data release (DR17) of APOGEE-2. Building on recent work, we fit median abundance ratio trends [X/Mg] versus [Mg/H] with a 2-process model, which decomposes abundance patterns into a "prompt"component tracing core-collapse supernovae and a "delayed"component tracing Type Ia supernovae. For each sample star, we fit the amplitudes of these two components, then compute the residuals δ[X/H] from this two-parameter fit. The rms residuals range from ∼0.01-0.03 dex for the most precisely measured APOGEE abundances to ∼0.1 dex for Na, V, and Ce. The correlations of residuals reveal a complex underlying structure, including a correlated element group comprised of Ca, Na, Al, K, Cr, and Ce and a separate group comprised of Ni, V, Mn, and Co. Selecting stars poorly fit by the 2-process model reveals a rich variety of physical outliers and sometimes subtle measurement errors. Residual abundances allow for the comparison of populations controlled for differences in metallicity and [α/Fe]. Relative to the main disk (R = 3-13 kpc), we find nearly identical abundance patterns in the outer disk (R = 15-17 kpc), 0.05-0.2 dex depressions of multiple elements in LMC and Gaia Sausage/Enceladus stars, and wild deviations (0.4-1 dex) of multiple elements in ω Cen. The residual abundance analysis opens new opportunities for discovering chemically distinctive stars and stellar populations, for empirically constraining nucleosynthetic yields, and for testing chemical evolution models that include stochasticity in the production and redistribution of elements.

Original languageEnglish (US)
Article number32
JournalAstrophysical Journal, Supplement Series
Issue number2
StatePublished - 2022
Externally publishedYes

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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