In 1995, the swiss #astronomers Michel Mayor and Didier Queloz discovered the first #exoplanet orbiting a #Sun-like #star: 51 Peg b. For that, they received the 2019 Physics' #Nobel Prize.
This discovery opened a new field of research in #astronomy. It was based on #observations done with the 1.93m #telescope at #HauteProvence #observatory (🇫🇷 ) with the instrument #ELODIE.
Below ⤵️ is a #thread presenting this instrument who allowed the discovery of 51Peg b.
#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.
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.
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.
However, in the mid-1990's when #ELODIE was developed, very few people actually managed to feed stellar light through fibers. It indeed requires a very precise optical alignment (with micro-lensing at the fiber entrance) and most attempt at the time led to low throughput. But André managed to do it, which was really an instrumental #breakthrough at that time.
We can see in this picture the same orange fibers entering the optical parts of the #ELODIE spectrograph.
Nowadays, most extreme precision radial-velocity instruments are still using this approach of fiber-fed spectrograph (although it has been marginally improved). This includes the ESPRESSO spectrograph at the 8.2m #ESO-VLT telescope in Chile, or the recently installed #KPF spectrograph on the 10m #Keck telescope in #Hawaii.
André's #breakthrough instrumental #achievement is still used now, almost 30 years later.
The second instrumental #breakthrough for the development of #ELODIE was to install the spectrograph in a stable, temperature controlled room, to avoid any deformation of the opto-mechanical elements that lead to instrumental radial velocity variation, that we want to avoid.
The pictures below show #ELODIE, sitting on a marble table and covered to limit thermal changes in its environment.
#ELODIE is a cross-dispersion spectrograph, meaning that the stellar light is first dispersed by a grating and then cross-dispersed by a prism. This makes spectrum to appear like a ladder (echelle in 🇫🇷 ) and not a single line spectrum. We call these kind of optical design an echelle spectrograph (see picture).
- 48 & 49: the fibers
- 38: the grating
- 42: the prism.
- 47: the CCD cooled by liquid nitrogen to -100ºC (-148°F).
Other optical elements are collimation mirrors.
All these optical elements can now be seen on the ground floor of the 1.93-m telescope at the #HauteProvence #Observatory (🇫🇷 ). Here are a few pictures of #ELODIE I took for you.
Although the #Nobel Prize 2019 was awarded to the 2 leading astronomers, the 51Peg b discovery was made possible thanks to a much broader team of technicians and engineers (here in 2005) from the #HauteProvence Observatory and the Marseille Observatory, especially André Baranne.
from left to right: J.-P. Berger, G. Knispel, J.-C. Baietto, G. Adrianzyk, D. Lacroix, A. Baranne, M. Mayor,
D. Queloz, D. Kohler, J.-P. Meunier, P. Véron, and P. Brunel.
A. Vin is missing in this picture.
Since 2006, #SOPHIE is replacing #ELODIE at the 1.93-m telescope and a major upgrade, #SOPHIERed, is planned for early 2023.
#SOPHIE is able to reach a radial velocity precision down to 1m/s.
SOPHIE is also in a thermally controlled room. I'm working with this instrument since 2009 and I never had the opportunity to actually see it (only on this picture). I was able to enter the temperature-controlled room only once, to perform some test / measurements.
Maybe next year for #SOPHIERed ?
References:
- http://obs-hp.fr/histoire/193/spectro_ELODIE.shtml (in 🇫🇷 )
- https://aas.aanda.org/articles/aas/pdf/1996/14/ds1106.pdf
Pictures are my own (A. Santerne / OHP-CNRS), from the #OHP / CNRS Images, or from Geneva Observatory.
I hope you enjoyed this thread.
Note that André Baranne passed away on 2021, January 26, at an age of 89.
This #thread aims to be for his honor.
Here is a picture I took of André Baranne (left) and Michel Mayor (right) in 2011 during the #CoRoT symposium. Michel was receiving a Doctorat Honoris Causa from the Aix-Marseille University #AMU.
Dr. Alexandre Santerne 🌍
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