Elevated r-process Enrichment in Gaia Sausage and Sequoia

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