Radial Velocity

The radial velocity technique was utilized to make the first exoplanet discoveries and continues to play a major role in the discovery and characterization of exoplanetary systems. In this chapter we describe how the technique works, and the current precision and limitations. We then review its major successes in the field of exoplanets. With more than 250 planet detections, it is the most prolific technique to date and has led to many milestone discoveries, such as hot Jupiters, multi-planet systems, transiting planets around bright stars, the planet-metallicity correlation, planets around M dwarfs and intermediate-mass stars, and recently, the emergence of a population of low-mass planets: ice giants and super-Earths. In the near future radial velocities are expected to systematically explore the domain of telluric and icy planets down to a few Earth masses close to the habitable zone of their parent star. They will also be used to provide the necessary follow-up observations of transiting candidates detected by space missions. Finally, we also note alternative radial velocity techniques that may play an important role in the future.