Astronomy and Astrophysics Supplement Series

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ELODIE: A spectrograph for accurate radial velocity measurements DOI: 10.1051/aas:1996251

Astronomy and Astrophysics Supplement Series, Vol. 119, October II 1996, 373-390

ELODIE: A spectrograph for accurate radial velocity measurements

A. Baranne , D. Queloz , M. Mayor , G. Adrianzyk , G. Knispel , D. Kohler , D. Lacroix , J.-P. Meunier , G. Rimbaud and A. Vin
Send offprint requests to: D. Queloz

Observatoire de Marseille, 2 Place Le Verrier, F--13248 Marseille, France
Observatoire de Genève, CH--1290 Sauverny, Switzerland
Observatoire de Haute--Provence, F--04870 Saint Michel l'Observatoire, France

Received September 28, 1995; accepted February 15, 1996

Abstract:

The fibre--fed echelle spectrograph of Observatoire de Haute--Provence, ELODIE, is presented. This instrument has been in operation since the end of 1993 on the 1.93 m telescope. ELODIE is designed as an updated version of the cross--correlation spectrometer CORAVEL, to perform very accurate radial velocity measurements such as needed in the search, by Doppler shift, for brown--dwarfs or giant planets orbiting around nearby stars. In one single exposure a spectrum at a resolution of 42000 (

) ranging from 3906 Å to 6811 Å is recorded on a 1024

1024 CCD. This performance is achieved by using a

echelle grating and a combination of a prism and a grism as cross--disperser. An automatic on--line data treatment reduces all the ELODIE echelle spectra and computes cross--correlation functions. The instrument design and the data reduction algorithms are described in this paper. The efficiency and accuracy of the instrument and its long term instrumental stability allow us to measure radial velocities with an accuracy better than 15ms

for stars up to 9th magnitude in less than 30 minutes exposure time. Observations of 16th magnitude stars are also possible to measure velocities at about 1kms

accuracy. For classic spectroscopic studies (

>100) 9th magnitude stars can be observed in one hour exposure time.

Key words: instrumentation: spectrographs --- methods: data analysis --- techniques: spectroscopic --- radial velocities