Accurate radial velocity determinations of optical emission lines (i.e., [Nii] λλ 6548, 6584, Hα and [S ii] λλ 6717, 6731) are very important for investigating the kinematic and dynamic properties of nebulae. The second stage survey program of Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST) has started a sub-survey of nebulae (MRS-N) which will spectroscopically observe the optical emission lines of a large sample of nebulae near the Galactic plane. Until now, 15 MRS-N plates have been observed from September 2017 to June 2019. Based on fitting the sky emission lines in the red band spectra of MRS-N, we investigate the precision of wavelength calibration and find there are systematic deviations of radial velocities (RVs) from ∼ 0.2 to 4 km s⁻¹ for different plates. Especially for the plates obtained in March 2018, the systematic deviations of RVs can be as large as ∼ 4 km s⁻¹, which then go down to ∼ 0.2 – 0.5 km s⁻¹ at the end of 2018 and January 2019. An RV calibration function is proposed for these MRS-N plates, which can simultaneously and successfully calibrate the systematic deviations and improve the precision of RVs.

光发射线的准确径向速度测定（即 [N ii ] λλ 6548、6584、H α和 [S ii] λλ 6717, 6731) 对于研究星云的运动学和动力学特性非常重要。大天区多目标光纤光谱望远镜（LAMOST）的第二阶段巡天计划已经启动了星云子巡天（MRS-N），它将在光谱上观察银河平面附近大量星云样本的光发射线。到现在为止，从2017年9月到2019年6月，已经观测到了15个MRS-N板块。基于对MRS-N红波段光谱的天空发射线拟合，我们研究了波长校准的精度，发现径向存在系统偏差。不同板块的速度（RV）从 ∼ 0.2 到 4 km s ^-1。特别是对于 2018 年 3 月获得的板块，RV 的系统偏差可高达 ∼ 4 km s ^-1，然后在 2018 年底和 2019 年 1 月下降到∼ 0.2 – 0.5 km s ^-1。针对这些 MRS-N 板提出了 RV 标定功能，可以同时成功标定系统偏差并提高精度房车。