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

Weinberg, David H. and Holtzman, Jon A. and Johnson, Jennifer A. and Hayes, Christian and Hasselquist, Sten and Shetrone, Matthew and Ting, Yuan-Sen and Beaton, Rachael L. and Beers, Timothy C. and Bird, Jonathan C. and Bizyaev, Dmitry and Blanton, Michael R. and Cunha, Katia and Fernandez-Trincado, Jose G. and Frinchaboy, Peter M. and Garcia-Hernandez, D. A. and Griffith, Emily and Johnson, James W. and Jonsson, Henrik and Lane, Richard R. and Leung, Henry W. and Mackereth, J. Ted and Majewski, Steven R. and Mészáros, Szabolcs and Nitschelm, Christian and Pan, Kaike and Schiavon, Ricardo P. and Schneider, Donald P. and Schultheis, Mathias and Smith, Verne (2022) Chemical Cartography with APOGEE: Mapping Disk Populations with a 2-process Model and Residual Abundances. ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, 260 (2). ISSN 0067-0049

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Abstract

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 Delta[X/H] from this two-parameter fit. The rms residuals range from similar to 0.01-0.03 dex for the most precisely measured APOGEE abundances to similar 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 [alpha/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 omega 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.

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