The Milky Way’s metal-poor stars are nearby ancient objects that are used to study early chemical evolution and the assembly and structure of the Milky Way. Here we present reliable metallicities of ∼280,000 stars with −3.75 ≲ [Fe/H] ≲ −0.75 down to g = 17 derived using metallicity-sensitive photometry from the second data release of the SkyMapper Southern Survey. We use the dependency of the flux through the SkyMapper v filter on the strength of the Ca ii K absorption features, in tandem with SkyMapper u, g, i photometry, to derive photometric metallicities for these stars. We find that metallicities derived in this way compare well to metallicities derived in large-scale spectroscopic surveys, and we use such comparisons to calibrate and quantify systematics as a function of location, reddening, and color. We find good agreement with metallicities from the APOGEE, LAMOST, and GALAH surveys, based on a standard deviation of σ ∼ 0.25 dex of the residuals of our photometric metallicities with respect to metallicities from those surveys. We also compare our derived photometric metallicities to metallicities presented in a number of high-resolution spectroscopic studies to validate the low-metallicity end ([Fe/H] < −2.5) of our photometric metallicity determinations. In such comparisons, we find the metallicities of stars with photometric [Fe/H] < −2.5 in our catalog show no significant offset and a scatter of σ ∼ 0.31 dex level relative to those in high-resolution work when considering the cooler stars (g − i > 0.65) in our sample. We also present an expanded catalog containing photometric metallicities of ∼720,000 stars as a data table for further exploration of the metal-poor Milky Way.

银河系的贫金属恒星是附近的古老天体，用于研究早期化学演化以及银河系的组装和结构。在这里，我们展示了 280,000 颗恒星的可靠金属丰度，其中 -3.75 ≲ [Fe/H] ≲ -0.75 低至g = 17，使用来自 SkyMapper 南方巡天第二次数据发布的金属丰度敏感光度法得出。我们使用通过 SkyMapper v过滤器的通量对 Ca ii K 吸收特征强度的依赖性，与 SkyMapper u , g , i 一起使用光度测量，以推导出这些恒星的光度金属丰度。我们发现以这种方式导出的金属丰度与大规模光谱调查中得出的金属丰度比较好，我们使用这种比较来校准和量化系统学作为位置、变红和颜色的函数。基于σ的标准偏差，我们发现与 APOGEE、LAMOST 和 GALAH 调查的金属丰度有很好的一致性∼ 0.25 dex 我们的光度金属量相对于这些调查的金属量的残差。我们还将我们导出的光度金属丰度与许多高分辨率光谱研究中提出的金属丰度进行比较，以验证我们的光度金属丰度测定的低金属丰度端 ([Fe/H] < -2.5)。在这样的比较中，我们发现在我们的目录中光度 [Fe/H] < -2.5 的恒星的金属丰度在考虑较冷的恒星时相对于高分辨率工作中的那些没有显着的偏移和σ ∼ 0.31 dex 水平的散射（克-我> 0.65) 在我们的样本中。我们还提供了一个包含约 720,000 颗恒星的光度金属丰度的扩展目录，作为进一步探索贫金属银河系的数据表。