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Metal-poor components of dwarf galaxies around the Milky Way could beremnants of the building blocks of the Galactic halo structure. Low-mass starsthat are currently observed as metal-poor stars are expected to have formed inchemically homogeneous clusters in the early phases of galaxy formation. Theyshould have already disintegrated and should exhibit large scatter in abundanceratios of some sets of elements (e.g., Sr/Ba) in the Milky Way field stars.However, chemical abundance ratios are expected to cluster in very metal-poorstars in dwarf galaxies because the number of clusters formed in individualgalaxies in the very early phase is expected to be quite limited. We examinethe possible clustering of abundance ratios of Sr and Ba in the Sextans dwarfgalaxy to test for the clustering star formation scenario. We investigate atotal of 11 elements (C, Mg, Ca, Sc, Ti, Cr, Mn, Ni, Zn, Sr, Ba) in five starsin the Sextans dwarf galaxy. Previous studies suggest that these have similarabundance ratios. In this study, we focus on the abundance ratio of Sr to Ba.The observations are based on high-resolution spectroscopy (R = 40 000) usingthe Subaru Telescope High Dispersion Spectrograph. The distribution of$\alpha$/Fe abundance ratios of the Sextans dwarf galaxy stars is slightlylower than the average of the values of stars in the Galactic halo. The Sr/Baabundance ratios for the five metal-poor stars are in good agreement, and thisclumping is distinctive compared to the [Sr/Ba] spread seen in the metal-poorhalo stars. We find that the probability of such clumping is very small if theSextans stars have distributions of Sr and Ba abundances similar to halo stars.

Chemical abundance analysis of extremely metal-poor stars in the Sextans dwarf spheroidal galaxy