(Proposal ID) S16A-079

(PI) Aoki, Misa

(Proposal Title)
Examination of Chemical Tagging for a Dwarf Galaxy

(Abstract)
Metal-poor components of dwarf galaxies around the Milky Way would be remnants 
of the building blocks of the Galactic halo structure. Low-mass stars that are 
currently observed as metal-poor stars are expected to have formed in 
chemically homogeneous clusters in the early phase of the galaxy formation. 
They should have already disintegrated and exhibit large scatter in abundance 
ratios of some sets of elements (e.g., Sr/Ba). However, clustering of chemical 
abundance ratios is expected in very metal-poor stars in dwarf galaxies, 
because the number of clusters formed in individual galaxies in the very early 
phase should be quite limited. Although the sample size is still limited, a 
signature of such clustering in Mg, Ca, and Ba abundance ratios is suggested 
for very metal-poor stars in the Sextans dwarf galaxy. We propose to obtain 
HDS spectra for the blue range to measure the Sr abundances for these stars. 
Since the abundance ratios of Sr/Fe and Sr/Ba of the field halo stars show 
extremely large scatter, these abundance ratios are the most critical test for 
the clustering star formation scenario.