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arXiv · 2012.01430

Elevated r-process enrichment in Gaia Sausage and Sequoia

David S. Aguado·Vasily Belokurov·G. C. Myeong·N. Wyn Evans·Chiaki Kobayashi·Luca Sbordone·Julio Chanamé·Camila Navarrete·Sergey E. Koposov
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Abstract

The Gaia Sausage (GS) and the Sequoia represent the major accretion events that formed the stellar halo of the Milky Way. A detailed chemical study of these main building blocks provides a pristine view of the early steps of the Galaxy's assembly. We present the results of the analysis of the UVES high-resolution spectroscopic observations at the 8.2m VLT of 9 Sausage/Sequoia members selected kinematically using Gaia DR2. We season this set of measurements with archival data from Nissen & Schuster (2011) and GALAH DR3 (2020). Here, we focus on the neutron-capture process by analysing Sr, Y, Ba and Eu behavior. We detect clear enhancement in Eu abundance ([Eu/Fe]~0.6-0.7) indicative of large prevalence of r-process in the stellar n-capture makeup. We are also able to trace the evolution of the heavy element production across a wide range of metallicity. The barium to europium changes from a tight, flat sequence with [Ba/Eu]=-0.7 reflecting dominant contribution from exploding massive stars, to a clear upturn at higher iron abundances, betraying the onset of contamination from asymptotic giant branch (AGB) ejecta. Additionally, we discover two clear sequences in [Fe/H]-[Ba/Fe] plane likely caused by distinct levels of s-process pollution and mixing within the GS progenitor.

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David S. Aguado, Vasily Belokurov, G. C. Myeong, N. Wyn Evans, Chiaki Kobayashi, Luca Sbordone, Julio Chanamé, Camila Navarrete, Sergey E. Koposov. 2020-12-02. Elevated r-process enrichment in Gaia Sausage and Sequoia. https://doi.org/10.3847/2041-8213%2Fabdbb8

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