HARPS: The Planet Hunter

HARPS is the ESO facility for the measurement of radial velocities with the highest accuracy currently available. It is fibre-fed by the Cassegrain focus of the 3.6m telescope in La Silla.

The instrument is built to obtain very high long term radial velocity accuracy (on the order of 1 m/s). To achieve this goal, HARPS is designed as an echelle spectrograph fed by a pair of fibres and optimised for mechanical stability. It is contained in a vacuum vessel to avoid spectral drift due to temperature and air pressure variations. One of the two fibres collects the star light, while the second is used to either record simultaneously a Th-Ar reference spectrum or the background sky. The two HARPS fibres (object + sky or Th-Ar) have an aperture on the sky of 1"; this produces a resolving power of 115,000 in the spectrograph. Both fibres are equipped with an image scrambler to provide a uniform spectrograph pupil illumination, independent of pointing decentering. The spectral range covered is 378nm-691nm, distributed over the echelle orders 89-161. As the detector consists of a mosaic of 2 CCDs (altogether 4k x 4k, 15 microns pixels), one spectral order (N=115, from 530nm to 533nm) is lost in the gap between the two chips.

HARPS produces a signal-to-noise ratio of 110 per pixel at 550nm for a Mv=6, G2V star, in 1 minute integration time (1" seeing, airmass = 1.2). When using the Simultaneous Thorium Reference Method (which is the standard mode for achieving the highest accuracy radial velocities) this signal-to-noise ratio should be sufficient to achieve a photon noise error on the radial velocity determination of about 0.90 m/s. Taking into account errors introduced by the guiding, focus, and instrumental uncertainties, a global radial velocity accuracy of about 1m/s RMS is achieved. This is attained for spectral type later than G and for non-rotating stars (v sin i < 2km/s).

In simultaneous Th-Ar mode, HARPS users should strictly follow the calibrations foreseen by the Calibration Plan, which includes a number of bias, flat field and Th-Ar exposures taken before the night.

HARPS is equipped with its own pipeline (installed at La Silla). This pipeline provides the visiting astronomer in near real-time with extracted and wavelength calibrated spectra in all observing modes. When the Simultaneous Thorium reference method is applied, the pipeline delivers precise radial velocities (RV, relative to the solar system barycentre) for late type stars whose RV is known within 1-2km/s, provided that a set of standard calibrations has been executed in the afternoon.

Project Milestone

May 1998 Announcement of Opportunity
February 2000 project kickoff
July 2000 Preliminary Design Review
March 2001 Final Design Review
December 2002 Preliminary Acceptance (Europe)
January 2003 Installation at La Silla
February 2003 Commissioning 1
March 2003 First Call for Proposals (for Period 72)
June 2003 Commissioning 2
October 1st 2003 Instrument offered to the community.

Project Details

Built under ESO contract by: Observatoire de Genève
Observatoire de Haute Provence
Universität Bern
Service d'Aéronomie
with substantial deliveries by ESO-La Silla, ESO-INS
Funded by Swiss National Science Foundation
Federal Office for Education and Research
La Région Provence, Alpes et Côte d'Azur
Institut National des Sciences de l'Univers INSU
Principal Investigator Michel Mayor (Geneva)
Project Scientists Didier Queloz (Geneva), Luca Pasquini (ESO Garching)
Project Managers Francesco Pepe (Geneva), Gero Rupprecht (ESO Garching)
Location La Silla 3.6m telescope, coudé west room
Project status Instrument available to the community (since 01/10/2003)
Instrument Science Team Joergen Christensen-Dalsgaard/Aarhus, Dainis Dravins/Lund, Martin Kürster/MPIA-Heidelberg, Artie Hatzes/Tautenburg, Francesco Paresce/ESO, Alan Penny/RAL
Work done by the HARPS Team

See also the HARPS web page in Geneva