# Properties of Radial Velocities measurement based on LAMOST-II Medium-Resolution Spectroscopic Observations

## TL;DR

This paper presents a detailed analysis of radial velocity measurements from LAMOST-II medium-resolution spectra, achieving high accuracy and precision through calibration and comparison with standard and reference stars.

## Contribution

It introduces a method for measuring radial velocities from LAMOST-II spectra with improved calibration and evaluates the measurement accuracy and precision.

## Key findings

- Measurement accuracy reaches 0.0227 km/s compared to standard stars.
- Intrinsic precision is 1.36 km/s at S/N=10, improving to 0.91 km/s at S/N=50.
- Method effectively calibrates and assesses radial velocity measurements for large spectral datasets.

## Abstract

The radial velocity (RV) is a basic physical quantity which can be determined through Doppler shift of the spectrum of a star. The precision of RV measurement depends on the resolution of the spectrum we used and the accuracy of wavelength calibration. In this work, radial velocities of LAMOST-II medium resolution (R ~ 7500) spectra are measured for 1,594,956 spectra (each spectrum has two wavebands) through matching with templates. A set of RV standard stars are used to recalibrate the zero point of the measurement, and some reference sets with RVs derived from medium/high-resolution observations are used to evaluate the accuracy of the measurement. Comparing with reference sets, the accuracy of our measurement can get 0.0227 km s/1 with respect to radial velocities standard stars. The intrinsic precision is estimated with the multiple observations of single stars, which can achieve to 1.36 km s/1,1.08 km s/1, 0.91 km s/1 for the spectra at signal-to-noise levels of 10, 20, 50, respectively.