Bright Metal-Poor Star Survey - I. Tomo-e Gozen narrow-band photometric survey and medium-resolution spectroscopic follow-up

Abstract

We present the Tomo-e Gozen Bright Metal-Poor Star Survey (TeMPS), a wide-area narrow-band photometric survey for bright metal-poor stars in the northern sky. The survey uses the Tomo-e Gozen camera on the 1.05 m Kiso Schmidt telescope with four narrow-band filters centered on the \ion{Ca}{2} H and K lines, the CH $G$ band, H$\alpha$, and a reference wavelength region. We review the survey strategy, photometric processing, and calibration of metallicity and carbon abundance estimates derived from narrow-band colors. We further present medium-resolution spectroscopic follow-up with Nayuta/MALLS to validate the photometric selection and identify new metal-poor stars. The current data set covers $\gtrsim 22,000$deg${}^2$ in all four bands with a total integration time of $\sim 100$ hr. The median limiting magnitudes at S/N = 20 correspond to $G\sim 12.5$. By combining narrow-band photometry with archival broad-band photometry and {\it Gaia} distances, we estimate $T\_\mathrm{eff}$, $\log (g)$, metallicity, and carbon abundance. Calibration against literature abundances derived from high-resolution spectra shows typical scatters of $<0.3$ dex in metallicity and $<0.4$ dex in carbon abundance. We estimate metallicities for $\sim 1.7$ million stars and identify $\sim 16,000$ very metal-poor candidates with [M/H]${}_{\mathrm{NB},\mathrm{fin}}<-2$. We show that Nayuta/MALLS medium-resolution spectra provide metallicities consistent with high-resolution measurements, with a scatter of $\sim 0.27$ dex. Among 32 photometrically selected candidates followed up with MALLS, 24 are confirmed to have [M/H]${}_{\mathrm{MALLS}}<-2$, including one newly identified star with [M/H]${}_{\mathrm{MALLS}}\simeq -3.4$. These results demonstrate that Tomo-e Gozen narrow-band photometry and MALLS medium-resolution spectroscopic follow-up efficiently select bright metal-poor stars for future high-resolution abundance studies. (abbreviated)

18 pages, 18 figures; submitted to PASJ on May 30 2026