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.
Carrillo, Andreia, et al. "The detailed chemical abundance patterns of accreted halo stars from the optical to infrared." Monthly Notices of the Royal Astronomical Society, vol. 513, no. 2, Apr. 2022. https://doi.org/10.1093/mnras/stac518
Carrillo, Andreia, Hawkins, Keith, Jofré, Paula, de Brito Silva, Danielle, Das, Payel, & Lucey, Madeline (2022). The detailed chemical abundance patterns of accreted halo stars from the optical to infrared. Monthly Notices of the Royal Astronomical Society, 513(2). https://doi.org/10.1093/mnras/stac518
Carrillo, Andreia, Hawkins, Keith, Jofré, Paula, et al., "The detailed chemical abundance patterns of accreted halo stars from the optical to infrared," Monthly Notices of the Royal Astronomical Society 513, no. 2 (2022), https://doi.org/10.1093/mnras/stac518
@article{osti_1866523,
author = {Carrillo, Andreia and Hawkins, Keith and Jofré, Paula and de Brito Silva, Danielle and Das, Payel and Lucey, Madeline},
title = {The detailed chemical abundance patterns of accreted halo stars from the optical to infrared},
annote = {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.},
doi = {10.1093/mnras/stac518},
url = {https://www.osti.gov/biblio/1866523},
journal = {Monthly Notices of the Royal Astronomical Society},
issn = {ISSN 0035-8711},
number = {2},
volume = {513},
place = {United Kingdom},
publisher = {Oxford University Press},
year = {2022},
month = {04}}
Brinson Foundation; Heising–Simons Foundation; Moore Foundation; National Fund for Scientific and Technological Development (FONDECYT); National Science Foundation (NSF); UK Research and Innovation Council; USDOE; USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC)
Grant/Contract Number:
NA0003843
OSTI ID:
1866523
Alternate ID(s):
OSTI ID: 1979565
Journal Information:
Monthly Notices of the Royal Astronomical Society, Journal Name: Monthly Notices of the Royal Astronomical Society Journal Issue: 2 Vol. 513; ISSN 0035-8711