Hansen, T. T.T. T.HansenMarshall, J. L.J. L.MarshallSimon, J. D.J. D.SimonLi, T. S.T. S.LiBernstein, R. A.R. A.BernsteinPace, A. B.A. B.PaceFerguson, P.P.FergusonNagasawa, D. Q.D. Q.NagasawaKuehn, K.K.KuehnCAROLLO, DanielaDanielaCAROLLOGeha, M.M.GehaJames, D.D.JamesWalker, A.A.WalkerDiehl, H. T.H. T.DiehlAguena, M.M.AguenaAllam, S.S.AllamAvila, S.S.AvilaBertin, E.E.BertinBrooks, D.D.BrooksBuckley-Geer, E.E.Buckley-GeerBurke, D. L.D. L.BurkeRosell, A. CarneroA. CarneroRosellKind, M. CarrascoM. CarrascoKindCarretero, J.J.CarreteroCostanzi, M.M.CostanziDa Costa, L. N.L. N.Da CostaDesai, S.S.DesaiDe Vicente, J.J.De VicenteDoel, P.P.DoelEckert, K.K.EckertEifler, T. F.T. F.EiflerEverett, S.S.EverettFerrero, I.I.FerreroFrieman, J.J.FriemanGarcía-Bellido, J.J.García-BellidoGaztanaga, E.E.GaztanagaGerdes, D. W.D. W.GerdesGruen, D.D.GruenGruendl, R. A.R. A.GruendlGschwend, J.J.GschwendGutierrez, G.G.GutierrezHinton, S. R.S. R.HintonHollowood, D. L.D. L.HollowoodHonscheid, K.K.HonscheidKuropatkin, N.N.KuropatkinMaia, M. A. G.M. A. G.MaiaMarch, M.M.MarchMiquel, R.R.MiquelPalmese, A.A.PalmesePaz-Chinchón, F.F.Paz-ChinchónPlazas, A. A.A. A.PlazasSanchez, E.E.SanchezSantiago, B.B.SantiagoScarpine, V.V.ScarpineSerrano, S.S.SerranoSmith, M.M.SmithSoares-Santos, M.M.Soares-SantosSuchyta, E.E.SuchytaSwanson, M. E. C.M. E. C.SwansonTarle, G.G.TarleVarga, T. N.T. N.VargaWilkinson, R.R.WilkinsonDES Collaboration2025-04-032025-04-0320200004-637Xhttp://hdl.handle.net/20.500.12386/37015We present a detailed abundance analysis of the three brightest member stars at the top of the giant branch of the ultrafaint dwarf (UFD) galaxy Grus II. All stars exhibit a higher than expected [Mg/Ca] ratio compared to metal-poor stars in other UFD galaxies and in the Milky Way (MW) halo. Nucleosynthesis in high-mass ( $\geqslant $ 20 M<SUB>☉</SUB>) core-collapse supernovae has been shown to create this signature. The abundances of this small sample (three) stars suggests the chemical enrichment of Grus II could have occurred through substantial high-mass stellar evolution, and is consistent with the framework of a top-heavy initial mass function. However, with only three stars it cannot be ruled out that the abundance pattern is the result of a stochastic chemical enrichment at early times in the galaxy. The most metal-rich of the three stars also possesses a small enhancement in rapid neutron-capture (r-process) elements. The abundance pattern of the r-process elements in this star matches the scaled r-process pattern of the solar system and r-process enhanced stars in other dwarf galaxies and in the MW halo, hinting at a common origin for these elements across a range of environments. All current proposed astrophysical sites of r-process element production are associated with high-mass stars, thus the possible top-heavy initial mass function of Grus II would increase the likelihood of any of these events occurring. The time delay between the α and r-process element enrichment of the galaxy favors a neutron star merger as the origin of the r-process elements in Grus II. <SUP>*</SUP> This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile....STAMPAenArticle10.3847/1538-4357/ab9643https://iopscience.iop.org/article/10.3847/1538-4357/ab96432020ApJ...897..183HFIS/05 - ASTRONOMIA E ASTROFISICA