S22B0114

We propose to obtain high-resolution, high-quality near infrared spectra of very metal-poor ([Fe/H]<−2) stars with IRD for accurate and precise measurements of Si abundances. Si is a key element for constraining early nucleosynthesis and chemical evolution in the Galaxy, but previous studies rely on only a few spectral lines in the optical range. Our recent study based on the previous run (S20A-101) established observation and abundance analysis procedures to obtain reliable Si abundances based on IRD spectra (Aoki et al. 2022). The approach is applied to a large sample of very metal-poor stars by this program. The goal is to determine the abundances with precision as good as 0.1 dex, which is much smaller than the scatter of [Si/Fe] ratios found by previous optical studies (∼ 0.3 dex), based on a much larger number of spectral lines than previous studies, for about 40 bright metal-poor stars. This program will enable us to determine abundance trends and scatter at low metallicity for Si, providing a standard data set that will be compared with chemical-evolution models. For this program 0.5 night is allocated on March 2022 (S22A-068N), in which 15-20 objects will be observed. Another one night in S22B will complete the program by observing 25 stars with different RA range than that of S22A.

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