The variability sky survey is a very effective method of searching for quasars. In the paper, we present a novel method to discriminate quasars from variable stars based on their intrinsic variabilities. The power-law model is used to fit the light-curve structure function in five wavebands, but the value of the structure function is normalized. The developed method is applied to 1411 spectroscopically confirmed quasars and 174 stars in SDSS stripe 82. We set a suitable criterion, then obtain a reasonable classified result. The classification accuracies about quasars and stars reach 92.2% and 83.6% respectively. Compared with the structure function only based on one physical parameter, the normalized structure function with amplitude and power-law index has a good efficiency to deal with these data. The method for selecting quasar candidates ensures big sky survey telescope a high survey efficiency and saving valuable astronomical observation time. The results support that the optical variabilities of most of quasars originate from the instabilities of accretion disks.%光变巡天是搜寻类星体的一个很有效的方法. 应用归一化结构函数对SDSS stripe 82中存在光变的1411个类星体和174个恒星进行分类, 选取幂函数模型拟合这些样本5个波段的结构函数. 综合幅值和幂指数两个物理量设置了合适的分类判据, 获得了比较理想的分类结果, 类星体和恒星最高分类正确率分别达到了92.2%和83.6%. 结果表明, 改正后的结构函数对类星体的证认有很好的效果, 能节约大型望远镜宝贵的观测时间, 让类星体巡天获得比较高的观测效率. 分析结论支持大部分类星体的光变缘于盘的不稳定性.
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