High-precision spectrographs for exoplanet research: CORAVEL, ELODIE, CORALIE, SOPHIE, and HARPS

Abstract

In this chapter, we will present the concepts, designs, and performances of several generations of simultaneous-reference spectrographs that have made the history of exoplanet discoveries by means of the Doppler technique. It is not possible to understand the strengths of this category of spectrographs without understanding first the revolutionary approach of CORAVEL that set the path for the next generation of instruments using CCDs, i.e., ELODIE and CORALIE. These instruments were extremely successful (e.g., with the discovery of 51 Peg b), it however quickly became clear that higher precision would be necessary in order not to remain stuck with Jupiter-and Saturn-mass planets only. The ELODIE/CORALIE concept was optimized in order to reach best possible performances. This process led to the development of HARPS that has become, through the tens of discoveries of Super-Earths and Neptunes, the new reference for high-precision Doppler velocity measurements. The success of HARPS had to be transposed to the northern hemisphere, an ambition that resulted first in the manufacturing of SOPHIE and later of HARPS-N. This work was finally the baseline for the development of ESPRESSO aiming at the next level of precision. We refer, however, to the chapter dedicated to ESPRESSO in this same handbook for a detailed description.