天文光学频率梳双通道同步定标系统消除光谱漂移的测试研究

The wavelength calibration of high resolution astronomical spectrographs with a laser frequency comb (LFC) can significantly increase the accuracy of radial velocity measurements (RV) to the precision of cm/s, this provides a powerful research tool for various cutting-edge scientific problems such as the detection of earth-like planets and the determination of the expansion of the universe and so on. The astrocombs with the frequency spacing of 25GHz is installed on the high resolution astronomical spectrograph of 2.16-meter telescope in Xinglong observatory, the precision improvement of the RV is strongly limited by the comb tooth shift, which is caused by the time-varying systematic effects, such the fluctuation of the pressure and the temperature, all the variation will decrease the calibration repeatability of the astrocombs. The dual mode fiber-fed calibration system of the laser optical comb for simultaneous wavelength calibration is designed, combining the calibration and the comb drift tracking of the LFC, the comb source is injected to the spectrograph with the different transmission path, which will provide two modes for calibration using the LFC during the long exposures, the standard operational mode and the simultaneous comparison mode. The two modes of the calibration provide an ideal reference comb line, combined with the mutual data analysis technique of the two comb tooth, obtained the calibration drift according to the systematic effects, the calibration can be revised by the obtained drift, with these modifications the LFC can meet the optimization of the calibration system. All works increase the stability of the optical frequency comb tooth and provide a theory insight to help the precision improvement of the RV.

天文光学频率梳用于光谱仪波长定标，可将视向速度测量精度提高到cm/s量级，从而为类地行星探测、宇宙膨胀加速度等前沿课题研究提供有力的工具。在我国2.16m望远镜安装天文光学频率梳后，外界环境微扰累积及系统误差引起的梳齿谱线漂移成为当前限制定标精度提高的主要因素。基于此，提出了天文光梳的双通道同步定标系统，结合天文光梳的定标功能和系统误差校正功能，将天文光梳通过不同传输路径导入光谱仪，为定标系统稳定性的精确计算提供参考梳齿，通过两种定标模式下的光梳梳齿对比定标算法，实现梳齿漂移的测量和定标精度的精确修正，为进一步提高光梳梳齿稳定性，提高视向速度测量精度提供理论指导。

提高视向速度的测量精度，是实现系外行星探索的关键技术之一。在北京兴隆观测站的2.16m望远镜光谱仪是中国目前可实现视向速度测量的主要仪器。其光谱仪分辨率是49800，光纤对天张角为2.4’’，光学频率梳做为新的定标光源在2016-2019年不断的安装和改进。为提高视向速度的测量精度，对定标系统和光纤连接系统进行了升级，双通道连接系统和八边形光纤振动扰模器的使用，使得系统获得稳定的定标光谱输出，通过汞灯实现平场测试，通过钍氩灯和光学频率梳进行光谱定标。在该系统下，光学频率梳定标精度达到0.36m/s，影响精度进一步提高的主要因素是光谱仪本底的漂移。