天文光梳双通道同步定标交叠光谱的视向速度算法研究

Astro-comb is the most promising high precision spectral calibration source of the next generation. The calibration precision level can reach as best as cm/s when it calibrates for the astronomical spectrograph. Owing to the limited stability of the spectrograph, the calibration ability of the astro-comb can only be brought into full play in the way of two-channel simultaneous calibration in general. 2.16m telescope high resolution spectrograph (HRS) is the first astronomical spectrograph in China which has been both equipped with the astro-comb and available for two-channel simultaneous calibration. However there is significant channel crosstalk for its simultaneous calibration raw spectra. This significant channel crosstalk makes it difficult for extracting the 1D spectra of a particular channel individually. And there will be large systematic errors in the extracted astro-comb's 1D spectra, thus the precision of radial velocity measurements will be worsen severely. Aiming at this issue, based on the cross-correlation function method, we proposed the creative algorithm for radial velocity measurement of the simultaneous calibration spectra having channel crosstalk. This algorithm steers clear of the difficult 1D spectrum extraction of a particular channel, but it is able to obtain the spectral drift and radial velocity of each channel by directly extracting the contaminated spectra. This algorithm is simple and free of those systematic errors. It is hopeful that the precision of radial velocity measurements for HRS can be highly improved by the use of this algorithm, and the astro-comb can better perform its calibration ability on HRS.

天文光梳是最具前景的下一代高精度光谱定标源，它为天文光谱仪定标，最高可以达到cm/s量级的定标精度。由于天文光谱仪稳定性有限，一般只有通过双通道同步定标的方式才能更好地发挥天文光梳的定标能力。2.16m望远镜高分辨率光谱仪（HRS）是国内首台配备天文光梳且具备双通道同步定标功能的天文光谱仪，然而它的双通道同步定标光谱有显著的通道交叠。这使得抽取不同通道独立的一维光谱变得困难，并且抽取的天文光梳一维光谱中会存在很大的系统误差，严重影响视向速度测量精度。针对这个问题，本项目创新性地提出了基于互相关函数法的双通道同步定标交叠光谱的视向速度算法，该算法巧妙绕开了抽取独立的一维光谱这个难点，只需抽取交叠光谱就能求出不同通道的光谱漂移量和视向速度，简化了算法的同时也克服了那些系统误差。将该算法应用于HRS天文光梳双通道同步定标，有望显著提高HRS的视向速度测量精度，更好地发挥天文光梳的定标能力。

本项目针对兴隆2.16-m望远镜高分辨率光纤光谱仪（HRS）的双通道交叠（crosstalk）问题进行研究。HRS双通道crosstalk显著，使得以传统数据处理方法来抽取不同通道独立的一维光谱变得困难，天文光梳的定标能力得不到充分发挥，并最终影响天体目标的视向速度测量精度。本项目试图从数据处理角度降低双通道crosstalk对定标精度的影响，从天文光梳在HRS的实测重复性定标精度、HRS线扩散函数的精确刻画、天文光梳在HRS的实测双通道同步定标精度三个方面展开研究，最终实现了在530～600 nm范围内0.15 m/s的光梳短期重复性定标精度与0.3 m/s的光梳双通道同步定标精度的结果。这个结果证明双通道crosstalk已得到了较好的抑制，HRS的双通道同步定标能够支撑m/s量级精度的视向速度测量。其中提出的主干-残差模型刻画光谱仪线扩散函数实现了0.6%的刻画精度，在降低双通道crosstalk影响的数据处理方法中起到了重要作用。