Characteristics
HARPS can attain a precision of 0.97 m/s (3.5 km/h), with an effective precision of the order of 30 cm s-1, making it one of only two instruments worldwide with such accuracy. This is thanks to a design in which the target star and a reference spectrum from a thorium lamp are observed simultaneously using two identical optic fibre feeds, and to very great attention to mechanical stability: the instrument sits in a vacuum vessel which is temperature-controlled to within 0.01 kelvins. The precision and sensitivity of the instrument is such that it incidentally produced the best available measurement of the thorium spectrum. Planet-detection is in some cases limited by the seismic pulsations of the star observed rather than by limitations of the instrument.
The principal investigator on HARPS is Michel Mayor who, along with Didier Queloz and Stéphane Udry have used the instrument to characterize the Gliese 581 system, home to one of the smallest known exoplanet orbiting a normal star, and two super-Earths whose orbits lie in the star's habitable zone.
It was initially used for a survey of a thousand stars.
Since october of 2012 the HARPS spectrograph has the precision to detect a new category of planets: Habitable super-Earths. This sensitivity was expected from simulations of stellar intrinsic signals, and actual observations of planetary systems.
Read more about this topic: High Accuracy Radial Velocity Planet Searcher