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Title: The formation of the milky way halo and its dwarf satellites: a NLTE-1D abundance analysis. IV. Segue 1, Triangulum  ii , and Coma Berenices UFDs
ABSTRACT We present atmospheric parameters and abundances for chemical elements from carbon to barium in metal-poor stars in Segue 1 (seven stars), Coma Berenices (three stars), and Triangulum ii (one star) ultrafaint dwarf galaxies (UFDs). The effective temperatures rely on new photometric observations in the visible and infra-red bands, obtained with the 2.5 m telescope of the SAI MSU Caucasian observatory. Abundances of up to fourteen chemical elements were derived under the non-local thermodynamic equilibrium (NLTE) line formation, and LTE abundances were obtained for up to five more elements. For the first time, we present abundance of oxygen in Seg 1 S1 and S4, silicon in ComaBer S2 and Tri ii S40, potassium in Seg 1 S1−S6 and ComaBer S1−S3, and barium in Seg 1 S7. Three stars in Segue 1, two stars in Coma Berenices, and Triangulum ii star have very low [Na/Mg] of −1.08 to −1.67 dex, which is usually attributed in the literature to an odd–even effect produced by nucleosynthesis in massive metal-free stars. We interpret this chemical property as a footprint of first stars, which is not blurred due to a small number of nucleosynthesis events that contributed to chemical abundance patterns of the sample stars. Our NLTE abundances of Sr and Ba in Coma Berenices, more » Segue 1, and Triangulum ii report on lower [Sr/Ba] abundance ratio in the UFDs compared to that in classical dwarf spheroidal galaxies and the Milky Way halo. However, in UFDs, just as in massive galaxies, [Sr/Ba] is not constant and it can be higher than the pure r-process ratio. We suggest a hypothesis of Sr production in metal-poor binaries at the earliest epoch of galactic evolution. « less
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Monthly Notices of the Royal Astronomical Society
Page Range or eLocation-ID:
1183 to 1200
Sponsoring Org:
National Science Foundation
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