HARPS spectrograph
The High Accuracy Radial velocity Planet Searcher (HARPS) is a high-precision echelle planet finding spectrograph installed in 2002 on the ESO's 3.6m telescope at La Silla Observatory in Chile. The first light was achieved in February 2003. HARPS has discovered over 130 exoplanets to date, with the first one in 2004, making it the most successful planet finder behind the Kepler space observatory. It is a second-generation radial-velocity spectrograph, based on experience with the ELODIE and CORALIE instruments.
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 due 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 careful 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 planetary 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.
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