On the radial velocity calibrations in the LAMOST medium-resolution spectroscopic survey of nebulae

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