Research On Estimating Stellar Atmospheric Parameters By SAGES And Gaia Photometric Data

With the massive data provided by various optical surveys,how to rapidly and accurately measure the atmospheric parameters for a large sample of stars has became a fundamental work in astrophysics research.Stellar atmospheric parameters are crucial to comprehensively describe the physical and chemical properties of stars in the Milky Way and further to understand the structure and evolution of the Milky Way.Sponsored by the National Astronomical Observatories of the Chinese Academy of Sciences,The SAGES（Stellar Abundance and Galactic Evolution Survey）plans to perform the medium/narrow-band photometric observation by means of a new photometric system(u,v,g,r,i,H_ɑw,H_ɑnand DDO51)covering about 12,000 square degree of northern sky.SAGES aims to obtain the atmospheric parameters for hundreds of millions of stars to help us to further study stellar elemental abundance and Galactic chemical evolution.Up to now,SAGES has generally completed the u,v band survey,and catalogs the u,v band photometric data of more than 50 million stars,covering 9960 square degrees of the north sky.Our work is to study the method of measuring the atmospheric parameters,based on the photometric data from SAGES and Gaia surveys,and to determine the atmospheric parameters of different types of stars in preparation for compiling the SAGES value-added catalogue.This paper includes the following two parts:（1）Polynomial fitting of the atmospheric parameters of red giant stars.First,limiting the range of colors and absolute magnitude in G,we construct a training sample of red giant stars.Then,using polynomial fitting method,we obtain the empirical formulae for estimating the metallicity[Fe/H]and effective temperature T_eff.We examine the accuracy of the two empirical formulae by comparing our results with measurements from spectroscopic survey LAMOST and APOGEE.In addition,using the uniformity of the metallicities for member stars of Globular Cluster,we further examine empirical formula of the metallicity.The results show that the effective range of metallicity can be as low as-2.5 dex and the uncertainty of metallicities is about 0.14 dex.The estimated range of effective temperature is 4000 to 5500K and the uncertainty of effective temperature is about 49 K.Finally,we constructed a catalog containing atmospheric parameters of 526,240 red giant candidates.（2）Estimating the metallicities of FGK type stars based on likelihood function.First,limiting the range of colors and absolute magnitude in G,we divide the training sample into giants and dwarfs training samples.Combing likelihood function,we use the two samples to build relation between colors and metallicities（i.e.,metallicities-dependent stellar loci）to estimate metallicities for giants and dwarfs,respectively.To examine the accuracy of metallicities estimated by colors,we compare our results with measurements from spectroscopic survey LAMOST and APOGEE.In addition,using the uniformity of the metallicity for wide binaries,we further examine the accuracy of metallicities estimated by colors.The results show that the metallicities estimated by the methodology appear useful down to-2.5 dex,-2 dex for giants and dwarfs,respectively.The uncertainty of photometeric metallicities is 0.19 dex,0.26 dex for giants and dwarfs,respectively.Finally,we constructed a catalog containing the metallicities for 543,310 giant stars and 3,917,904 dwarf stars.