Sulfur Abundances in Metal-Poor Stars Based on OAO-1.88 m/HIDES Spectra

The LTE abundances of sulfur (S) of 21 metal-poor stars and one normal star were explored in the metallicity range of $-3 < \mathrm{[Fe/H]} \leq 0$, based on the equivalent widths of the S I (1) 9212, 9237 Å and S I (6) 8693, 9894 Å lines measured on high-resolution spectra, which were observed by the OAO 1.88-m telescope equipped with HIDES. Our main results are: (1) The abundances derived from the S I (6) lines are consistent with those from the S I (1) lines among our sample stars in the range of $\mathrm{[Fe/H]} \gt-2 \mathrm{[Fe/H]} \gt-2$ with an average difference of $+0.03 \pm 0.05 \,\mathrm{dex}$, whereas a significant discrepancy is observed in the range of $\mathrm{[Fe/H]} \leq-2$. (2) The behavior of $\mathrm{[S(6)/Fe]}$ versus $\mathrm{[Fe/H]}$ of our halo sample stars exhibits a nearly flat trend with an average of $+0.62 \pm 0.09 \,\mathrm{dex}$ in the range of $-3 < \mathrm{[Fe/H]} <-1.25$, and shows a distribution around $+0.29 \,\mathrm{dex}$ in $-1.25 \leq\mathrm{[Fe/H]}\leq-0.7$. Our sample stars with $-1.25 \leq \mathrm{[Fe/H]} \leq-0.5$ follow an increasing trend with decreasing $\mathrm{[Fe/H]}$. The behavior of $\mathrm{[S(1)/Fe]}$ of our sample stars also shows essentially the same trend as $\mathrm{[S(6)/Fe]}$, though it is quantitatively different. (3) The S behavior in the range of $-3 < \mathrm{[Fe/H]} \leq 0$ inferred from the abundances of multiplets 6 and 1 are qualitatively consistent with each other, and may be represented by a combination of a nearly flat trend and a linearly increasing trend with decreasing $\mathrm{[Fe/H]}$. A transition of the trend is likely to occur at $\mathrm{[Fe/H]} \sim-1.5 \,\mathrm{dex}$.