A similar instrument, HARPS-N, has been implemented and installed on the 3.6-m Italian Telescopio Nazionale Galileo at La Palma, Canary Islands in Spain in 2012, allowing astronomers to search for exoplanets with the radial velocity method from both hemispheres. mounted on the ESO 3.6 m telescope in La Silla in Chile. Indeed, discoveries of the vast majority of exoplanets via the radial velocity method is only possible with the High Accuracy Radial velocity Planet Searcher (HARPS), a high precision echelle spectrograph built by Mayor et al. As can be imagined, to reveal the small perturbation caused by planetary companion in the host star’s radial velocity, it requires very precise measurement of radial velocity, which is only possible via very high resolution spectrograph. The downside of the radial velocity method is that we do not know the inclination of the planetary orbit, so the interpreted planetary mass is always the lowest possible value, and the true mass can be much heavier if we are observing the planetary system in a almost face-on view. While the result received a vast amount of critics, especially with the speculations that such kind of radial velocity signal could be mimicked by stellar spots, it has turned out that the radial velocity signal is truly coming from a planetary mass companion. The idea is, if there is an unseen planetary mass companion to the host star, they will both exhibit orbital motion around the common mass center, rendering periodic blue and redshift of emission and/or absorption lines in the host star’s spectra due to the Doppler effect. ![]() The first exoplanet around solar like stars-51 Pegasi b-was found by a radial velocity method by Mayor and Queloz in 1995. Interestingly, the very first extra-solar planets (hereafter exoplanets) were not found around a main-sequence star, but rather an neutron star using the change in pulsar timing. Searching for and characterization of planets beyond the solar system has been a long quest for observational astronomy. In this article, I present a concise review of the extra-solar planet discoveries, discussing the strengths and weaknesses of the major planetary detection methods, providing an overview of our current understanding of planetary formation and evolution given the tremendous observations delivered by various methods, as well as on-going and planned observation endeavors to provide a clear picture of extra-solar planetary systems. The exquisite AO imaging from ground-based large telescopes, coupled with high-contrast coronagraph, captured the photons directly emitted by planets around other stars. Ultra wide-field, high cadence, continuous monitoring of the Galactic bulge from different sites around the southern hemisphere provides us the opportunity to observe microlensing effects caused by planetary systems from the solar neighborhood, all the way to the Milky Way center. ![]() High precision photometry from the space, especially with the Kepler mission, enables us to detect planets when they transit their stars and dim the stellar light by merely one percent or smaller. Thanks to high precision spectrographs, we are able to reveal unseen companions to stars with the radial velocity method. ![]() Our understanding of extra-solar planet systems is highly driven by advances in observations in the past decade.
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