The third instrumental #breakthrough was to use digital detectors (CCD) that started to be used in astronomy in the late 80's / early 90's. #ELODIE was developed in 1994 so this technology was pretty new in #astronomy. CCDs offer much more stable and precise measurements. They also have many pixels allowing to record the entire visible spectrum at once (see picture). In comparison, #CORAVEL was using a (1-px) photo-multiplicator to measure the stellar light.

To improve the radial velocity precision, #ELODIE had to be a much more stable instrument, in a temperature- and pressure-controlled environment which was not compatible with the dome.

So, André Baranne (a french astronomer at Marseille Observatory who also built #CORAVEL in 1977) suggested to use optical #fibers to feed the stellar light from the #telescope to the instrument. We can see these fibers in orange in this picture of the bonnette, mounted on the 1.93-m telescope at #HauteProvence.

The jump in precision between the #CORAVEL (300m/s) and the #ELODIE (10m/s) spectrographs was due to several achievements.

CORAVEL was mounted directly on the back of the swiss telescopes at either the #HauteProvence or #LaSilla observatories. In such case, the instrument's #optical and #mechanical components are deformed by #temperature, #humidity and the position of the telescope. Such deformation was a clear limitation to the radial velocity precision.

#ELODIE is a #spectrograph that was able to measure the radial velocity of #stars via the #Doppler effect with a precision down to about 10m/s.

It is actually the successor of the #CORAVEL spectrograph with which Michel Mayor & Antoine Duquennoy studied the population of binary stars in the #solar neighborhood. #CORAVEL had a precision down to about 300m/s which is not enough to discover (most) exoplanets.

#ELODIE is thus a super coravel.