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Abstract Using multielement abundances from the Sloan Digital Sky Survey APOGEE survey, we investigate the origin of abundance variations in Milky Way (MW) disk stars on the “high- α plateau,” with −0.5 ≤ Mg/H ≤ −0.1 and 0.25 ≤ Mg/Fe ≤ 0.35. The elevated α /Fe ratios of these stars imply low enrichment contributions from Type Ia supernovae (SN Ia), but it is unclear whether their abundance patterns reflect pure core-collapse supernova (CCSN) enrichment. We find that plateau stars with higher Fe/Mg ratios also have higher X/Mg ratios for other iron-peak elements, suggesting that the Fe/Mg variations in the plateau population do reflect variations in the SN Ia/CCSN ratio. To quantify this finding, we fit the observed abundance patterns with a two-process model, calibrated on the full MW disk, which represents each star’s abundances as the sum of a prompt CCSN process with amplitude A cc and a delayed SN Ia process with amplitude A Ia . This model is generally successful at explaining the observed trends of X/Mg with A Ia / A cc , which are steeper for elements with a large SN Ia contribution (e.g., Cr, Ni, Mn) and flatter for elements with low SN Ia contribution (e.g., O, Si, Ca). Our analysis does not determine the value of Mg/Fe corresponding to pure CCSN enrichment, but it should be at least as high as the upper edge of the plateau at Mg/Fe ≈ 0.35, and could be significantly higher. Compared to the two-process predictions, the observed trends of X/Mg with A Ia / A cc are steeper for (C+N) but shallower for Ce, providing intriguing but contradictory clues about asymptotic giant branch enrichment in the early disk.
Sit et al. (Thu,) studied this question.