Radial Velocity Measurement of the DA White Dwarfs

White Dwarfs (WDs) are the final stage of the evolution of the majority of low-and medium-mass stars with initial mass <8M_⊙. Approximately 75% of all observed WDs are DA type. The spectra of DA white dwarf are dominated with Balmer Hydrogen lines. It is very difficult to measure the APP radial velocity of WDs by the line center because of the wide and asymmetry spectral profile. The kinematics of WDs is very important to distinguish populations of WDs. This paper presents a method for APP radial velocity measurement using cross-correlation between the observed spectrum and the template spectrum that has similar parameters, which has advantage than line center method, and the template spectra are from theoretical spectra by Koster et al. The final radial velocity is derived by the difference of APP radial velocity and the gravitational redshift. After test with simulated spectrum, the accuracy is within 10km/s for DA white dwarfs with T_eff higher than 10000K and SNR larger than 20. In addition, the radial velocities of observed DA WDs from SDSS DR7 are measured with the above method. The average radial velocities of these close DA white dwarfs (distance <1000pc) are approaching zero.