The detailed chemical abundance patterns of accreted halo stars from the optical to infrared

Carrillo, Andreia; Hawkins, Keith; Jofré, Paula; de Brito Silva, Danielle; Das, Payel; Lucey, Madeline

Abstract

Understanding the assembly of our Galaxy requires us to also characterize the systems that helped build it. In this work, we accomplish this by exploring the chemistry of accreted halo stars from Gaia-Enceladus/Gaia-Sausage (GES) selected in the infrared from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) Data Release 16. We use high resolution optical spectra for 62 GES stars to measure abundances in 20 elements spanning the α, Fe-peak, light, odd-Z, and notably, the neutron-capture groups of elements to understand their trends in the context of and in contrast to the Milky Way and other stellar populations. Using these derived abundances we find that the optical and the infrared abundances agree to within 0.15 dex except for O, Co, Na, Cu, and Ce. These stars have enhanced neutron-capture abundance trends compared to the Milky Way, and their [Eu/Mg] and neutron-capture abundance ratios (e.g. [Y/Eu], [Ba/Eu], [Zr/Ba], [La/Ba], and [Nd/Ba]) point to r-process enhancement and a delay in s-process enrichment. Their [α/Fe] trend is lower than the Milky Way trend for [Fe/H] > −1.5 dex, similar to previous studies of GES stars and consistent with the picture that these stars formed in a system with a lower rate of star formation. This is further supported by their depleted abundances in Ni, Na, and Cu abundances, again, similar to previous studies of low-α stars with accreted origins.

Citation

Carrillo, A., Hawkins, K., Jofré, P., de Brito Silva, D., Das, P., & Lucey, M. (2022). The detailed chemical abundance patterns of accreted halo stars from the optical to infrared. Monthly Notices of the Royal Astronomical Society, 513(2), 1557-1580. https://doi.org/10.1093/mnras/stac518

• Journal Article Type: Article
• Acceptance Date: Feb 21, 2022
• Online Publication Date: Apr 28, 2022
• Publication Date: 2022-06
• Deposit Date: Jun 23, 2022
• Publicly Available Date: Jun 23, 2022
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Royal Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 513
• Issue: 2
• Pages: 1557-1580
• DOI: https://doi.org/10.1093/mnras/stac518
• Public URL: https://durham-repository.worktribe.com/output/1203257