SAGE巡天介绍I——测光系统和数据处理

摘要

SAGE(Stellar Abundance and Galactic Evolution)巡天采用一套对恒星大气参数敏感的独特测光系统,包括uSC,vSAGE,g,r,i,Hαn,Hαw和λDDO51(David Dunlap Observatory,DDO)共8个波段.该系统对恒星大气参数(有效温度Teff、表面重力lg g 和金属丰度[Fe/H])和星际消光的测量比传统的uvbyβ 系统(Str?mgren-Crawford,SC)更敏感.由于g,r,i波段带宽较宽,因而观测效率较高,对恒星大气参数的测量精度和观测效率均超过uvbyβ系统和宽带测光系统.利用美国亚利桑那大学Steward 天文台2.3 m Bok 望远镜、新疆天文台南山1 m 望远镜和乌兹别克斯坦MAO(Maidanak Astronomical Observatory)1 m 望远镜已展开巡天观测.项目计划在约4 年时间内完成所有的巡天观测,北天天区覆盖面积约12 000(°)2,高精度测光(信噪比为100σ)深度约15 mag(V 波段);5σ 探测极限可深至约20 mag(V 波段).最终将探测约5×108颗恒星,并得出其恒星大气参数以及星际消光.该样本比之前的u,v,b,y,β 测光巡天,如GCS(Geneva-Copenhagen Survey)巡天和HM(Hauck and Mermilliod 1998)巡天,扩展到更深的区域,即深度达到7~8 mag(V波段).利用观测得到的大样本恒星测光星表,可以开展如下课题的研究:(1)得到银河系约5×108颗恒星大样本的金属丰度分布,并根据恒星演化模型得到其年龄分布;(2)预期搜寻到一批贫金属星候选体,并利用其他望远镜进行下一步观测;(3)结合高质量的uSC波段数据,预期可以找到一批白矮星;(4)结合其他星表,预期找到一批长周期变源以及移动天体;(5)结合uSC波段数据和其他星表,预期可以找到一批类星体.%The SAGE(Stellar Abundance and Galactic Evolution)survey utilizes a special photometric system,which includes 8 bands in total,uSC,vSAGE,g,r,i,Hαw,Hαnand λDDO51.Compared to the uvbyβ system,the SAGE system is designed more sensitive to the stellar atmospheric parameters(i.e.,effective temperature Teff,surface gravity lg g and metallicity [Fe/H])and interstellar extinction.The system is also more efficient in observations as the bandwidths of g,r,i bands are much wider than those of the uvbyβ system.Therefore,the accuracy of the stellar parameter measurement of the SAGE system could actually exceed that of the broadband photometry.Three telescopes(2.3-m Bok telescope of Steward Observatory of University of Arizona,Nanshan 1-m telescope of Xinjiang Astronomical Observatory and Maidanak Astronomical Observatory(MAO)1-m telescope of Uzbekistan)are used and all the observations of the survey will be completed within about 4 years.The footprint is more than 12 000(°)2of the north sky and the magnitude coverage of the high precision photometry is about 15 mag(100σ)in V-band; the 5σ detection limit is about 20.0 mag in V-band.Finally in total about 0.5 billion stars will be detected,and the stellar atmospheric parameters as well as the interstellar extinction will be determined.The SAGE survey actually could extend about 7~8 mag(V-band)fainter than the previous uvbyβ survey,e.g.,the Geneva-Copenhagen Survey(GCS)and the HM survey.