暗弱天体自行星表GPS2的构建及其在恒星年龄精确测量中的应用

The large proper motion catalog GPS1 released in 2017 has played an important role in many scientific researches. However, GPS1 does not include those objects fainter than 20 mag in r-band. Meanwhile, the faint objects in the upcoming Gaia DR2 may not be able to reach a precision of sub-mas/yr. In order to significantly improve the proper motions of fainter objects (19<mr<23 mag), we propose to combine the photometric positions with the long time baseline positions provided by PS1 and SDSS with Gaia DR2, to upgrade GPS1, and release one of the deepest proper motion catalogs in the world (dubbed GPS2). GPS2 will be an excellent complement and extension to Gaia DR2, and an important proper motion source before the next generation surveys (e.g. LSST).. Based on the proper motion, trigonometric parallax and radial velocity, we also propose to search for white dwarf-main sequence (WD-MS) binaries from the GPS2, Gaia DR2, and LAMOST, and use the WD-MS samples to measure the stellar age of low mass (smaller than one solar mass) stars, which could make up the shortcoming of the classic methods, such as asteroseismology, gyrochronology etc., for the age estimation of low mass stars. The precision of stellar age can be improved by a factor of 2~3 in this project.

申请人发布的大型自行星表GPS1已在国际上得到了广泛的应用，并发挥了重要作用。但GPS1星表未包括暗于20等天体自行，同时即将发布的Gaia DR2中暗弱天体的自行可能无法达到亚毫角秒每年精度，为此本课题提出：通过结合PS1、SDSS等长时间基线的测光数据，显著提高暗弱天体（19<mr<23 mag）的自行精度，发布国际上最深的高质量大型自行星表GPS2。GPS2将及时补充和扩展GPS1、Gaia星表，且对下一代巡天（如LSST）有重要的承上启下意义。. 作为GPS2一个典型的科学应用，该课题还将借助GPS2、Gaia DR2等星表在自行、三角视差等方面的优势，搜寻并利用白矮-主序双星样本开展精确测量低质量恒星年龄的研究，弥补星震学等经典方法在年龄测量方面的不足，将恒星年龄的测量精度提高2-3倍。

在该项目的支持下，负责人及其团队成员在原来构建的GPS1的基础上，完成了4亿多颗暗弱天体的自行测量，平均自行精度达亚毫角秒每年（sub-mas/yr），发布了GPS1+自行星表。利用GPS1+、Gaia以及我国自主设计完成的郭守敬望远镜（LAMOST）巡天数据，完成了以下科学研究内容：（1）利用白矮-主序（WD-MS）双星精确测量主序星的年龄；（2）搜寻远距双星，并利用其限制MACHO银晕暗物质模型；（3）首次发现宽距“双胞胎”星比例异常；（4）发现太阳邻域年轻星族巨型恒星结构；（5）揭示出银晕恒星的化学-动力学规律；（6）精确测量出银河系质量；（8）详细研究了恒星“蛇”的整体结构及属性特征。这些成果为我们深入理解银河系的形成及结构演化提供了不可或缺的观测证据。

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