We propose to obtain high-resolution ultra-violet (UV) spectra of unevolved very metal-poor ([Fe/H]<−2) stars with HDS to determine nitrogen abundances from NH molecular band. Nitrogen abundances are a good tracer of contributions of mass-loss from massive stars with high rotational velocity to the early chemical evolution, which are predicted but not well constrained by observations. For this purpose, nitrogen abundances need to be determined for unevolved stars because the surface nitrogen abundance could be changed by internal process in the red giant phase in low-mass stars that are currently observed as metal-poor stars. The observations have been limited because of the difficulty to obtain high resolution UV spectra covering the NH band at 3360 Å. To expand the sample of unevolved stars several times, we will conduct the observations for 35 very metal-poor stars with Subaru/HDS that has advantages in efficiency thanks to the high altitude of the telescope site and the high throughput in the ultraviolet range. The abundance trend and scatter of nitrogen will examine the contributions of mass-loss of rotating massive stars to the bulk of the Milky Way halo and also constrain the impact of individual sources to the chemical evolution.
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