We develop a method to estimate photometric metallicities by simultaneously fitting the dereddened colors u-g, g-r, r-i and i-z from the SDSS with those predicted by the metallicity-dependent stellar loci. The method is tested with a spectroscopic sample of main-sequence stars in Stripe 82 selected from the SDSS DR9 and three open clusters. With 1 per cent photometry, the method is capable of delivering photometric metallicities precise to about 0.05, 0.12, and 0.18 dex at metallicities of 0.0, -1.0, and -2.0, respectively, comparable to the precision achievable with low-resolution spectroscopy at a signal-to-noise ratio of 10. We apply this method to the re-calibrated Stripe 82 catalog and derive metallicities for about 0.5 million stars of colors 0.3 < g-i < 1.6 mag and distances between 0.3 -- 18 kpc. Potential systematics in the metallicities thus derived, due to the contamination of giants and binaries, are investigated. Photometric distances are also calculated. About 91, 72, and 53 per cent of the sample stars are brighter than r = 20.5, 19.5, and 18.5 mag, respectively. The median metallicity errors are around 0.19, 0.16, 0.11, and 0.085 dex for the whole sample, and for stars brighter than r = 20.5, 19.5, and 18.5 mag, respectively. The median distance errors are 8.8, 8.4, 7.7, and 7.3 per cent for the aforementioned four groups of stars, respectively. The data are publicly available. Potential applications of the data in studies of the distribution, (sub)structure, and chemistry of the Galactic stellar populations, are briefly discussed. The results will be presented in future papers.
Gaia FGK Benchmark Stars: spectral library, metallicities and abundances of $α$ and Fe-peak elements of the third version
LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS（巴黎天文台，PSL大学，索邦大学，巴黎西岱大学，塞吉-蓬图瓦兹大学，法国国家科学研究中心）；Laboratoire d’Astrophysique de Bordeaux, Univ. Bordeaux, CNRS（波尔多大学，法国国家科学研究中心）；Instituto de Estudios Astrofísicos, Facultad de Ingeniería y Ciencias, Universidad Diego Portales（迭戈·波特莱斯大学工程与科学学院天体物理研究所）；Harvard-Smithsonian Center for Astrophysics（哈佛-史密森尼天体物理中心）；Faculty of Psychology, UniDistance Suisse（瑞士远程教育大学心理学学院）；Observational Astrophysics, Department of Physics and Astronomy, Uppsala University（乌普萨拉大学物理与天文系观测天体物理学）；Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM（巴黎萨克雷大学，巴黎西岱大学，法国原子能和替代能源委员会）
The Pristine survey XXIX. Data Release 2: Photometric metallicities for 15 millions stars down to $G\sim 20.5$
School of Astronomy and Space Science, Nanjing University（南京大学天文与空间科学学院）；Key Laboratory of Modern Astronomy and Astrophysics, Nanjing University, Ministry of Education（南京大学现代天文与天体物理教育部重点实验室）；Institute of Astronomy, University of Cambridge（剑桥大学天文学研究所）；Université de Strasbourg, CNRS, Observatoire astronomique de Strasbourg, UMR 7550（斯特拉斯堡大学、法国国家科学研究中心、斯特拉斯堡天文台）；Max-Planck-Institut für Astronomie（马克斯·普朗克天文学研究所）；Kapteyn Astronomical Institute, University of Groningen（格罗宁根大学卡普坦天文研究所）；LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS（巴黎天文台 LIRA 实验室、巴黎文理研究大学、索邦大学、巴黎西岱大学、塞吉-蓬图瓦兹大学、法国国家科学研究中心）；Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange（蔚蓝海岸大学、蔚蓝海岸天文台、法国国家科学研究中心、拉格朗日实验室）
Chemical abundances of 1111 FGK stars from the HARPS GTO planet search program IV. Carbon and C/O ratios for Galactic stellar populations and planet hosts
Photometric Metallicities for 367,324 stars of Omega Centauri
Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University（北京师范大学前沿天体物理研究所）；School of Physics and Astronomy, Beijing Normal University（北京师范大学物理与天文学院）；Department of Physics and Astronomy, University of Notre Dame（圣母大学物理与天文系）；Joint Institute for Nuclear Astrophysics – Center for the Evolution of the Elements (JINA-CEE)（核天体物理联合中心——元素演化中心）
Gaia FGK benchmark stars: Abundances of n-capture elements of the third version
Instituto de Astrofísica de Canarias（加那利天体物理学研究所）；Universidad de La Laguna（拉帕鲁尼亚大学）；Instituto de Estudios Astrofísicos, Facultad de Ingeniería y Ciencias, Universidad Diego Portales（迭戈·波特莱斯大学工程与科学学院天体物理研究所）；LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS（巴黎天文台LIRA实验室（隶属PSL大学、索邦大学、巴黎西岱大学、CY塞尔吉-巴黎大学及法国国家科学研究中心））；Laboratoire d’Astrophysique de Bordeaux, Univ. Bordeaux, CNRS（波尔多大学天体物理学实验室（隶属法国国家科学研究中心））；Observational Astrophysics, Department of Physics and Astronomy, Uppsala University（乌普萨拉大学物理与天文学系观测天体物理学）；Instituto de Astrofísica, Pontificia Universidad Católica de Chile（智利天主教大学天体物理研究所）；Harvard-Smithsonian Center for Astrophysics（哈佛-史密森尼天体物理中心）；Faculty of Psychology, UniDistance Suisse（瑞士远程大学心理学学院）
