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Early chemical enrichment of the Milky Way dwarf satellites from high-resolution and NLTE analysis of VMP stars

2018; Cambridge University Press; Volume: 14; Issue: S344 Linguagem: Inglês

10.1017/s1743921318005318

1743-9221

L. Mashonkina, P. Jablonka, T. Sitnova, Yuri Pakhomov, P. North, А. М. Татарников, М. А. Бурлак, O. V. Vozyakova,

Astrophysics and Star Formation Studies

Abstract We present the NLTE abundances of 10 chemical species in 65 very metal-poor stars in eight dSphs and the Milky Way halo. The classical dSphs Sculptor, Ursa Minor, Sextans, and Fornax reveal a similar plateau at [α/Fe] = 0.3 for each of Mg, Ca, and Ti, similarly to the MW halo. We provide the evidence for a decline in α/Fe in the Boötes I UFD, that is probably due to the ejecta of SNeIa. The dichotomy in the [Sr/Ba] versus [Ba/H] diagram is observed in the classical dSphs, similarly to the MW halo, calling for two different nucleosynthesis channels for Sr. The Boötes I and UMa II UFDs reveal very similar ratios of [Sr/Mg] = −1.3 and [Ba/Mg] = –1. The stars in the Coma Berenices and Leo IV UFDs are even poorer in Sr and Ba. The subsolar Sr/Ba ratios of Boötes I and UMa II indicate a common r-process origin of their n-capture elements.