First images for the NIRPS spectrograph

The NIRPS spectrograph, whose design is led by a team from the Observatoire du Mont-Mégantic (OMM), the Centre d’optique photonique et laser (COPL) and the Institute for Research on Exoplanets (iREx), in association with engineers from the NRC Herzberg Institute of Astrophysics, obtained its very first images in August in the Université Laval’s laboratory. This is an important step before the instrument is installed on the 3.6-m telescope in La Silla, Chile, and can begin its study of exoplanets.  

NIRPS (Near InfraRed Planet Searcher) is a spectrograph built by an international collaboration led by René DoyonDirector of both the OMM and iREx, and François BouchyUniversité de Genève’s Observatoire astronomique. Operating in infrared light, NIRPS is optimised to study Earth-sized exoplanets orbiting cooler stars. It should be in operation in 2021 at the 3.6-meter telescope at La Silla, Chile, operated by ESO (European Southern Observatory). 

“We’ve been working on NIRPS for five years,” explains Étienne ArtigauiREx Researcher and NIRPS Project Scientist. “It is very motivating for the scientific team to realise that we are no more than a few months away from starting the search for exoplanets with this instrument. » 

First thermal cycle 

The instrument’s assembly was carried out over the spring and part of the summer of 2020 at Université Laval laboratories under the supervision of Simon ThibaultProfessor at the Université Laval, member of the COPL and iREx Associate Member. The team then began the instrument’s first “thermal cycle” on July 31. This step consists of assembling all the optical elements and aligning them with great precision in the cryostat, an enclosure that keeps the instrument at very cold temperatures. 

 

The team closing the cryogenic chamber on July 31 2020, in the laboratories of the Université Laval’s COPL. From left to right: Lison Malo (iREx, OMM, UdeM), Anne-Sophie Poulin-Girard (COPL, ULaval), Hugues Auger (COPL, ULaval) and Philippe Vallée (OMM, UdeM). Photo credit: Lison Malo.

The spectrograph is made up of five zinc selenide (ZnSe) prisms, an optical material ideal for infrared observations. It separates light into an infrared rainbow invisible to the naked human eye ranging from 0.97 to 1.81µm. 

“It’s quite a puzzle to assemble the instrument,” says Philippe ValléeInstrumentation Specialist at the Observatoire du Mont-Mégantic. “You have to understand that all components are installed at room temperature. Glass parts shrink much less than aluminum parts when they cool down. One small error in calculation or assembly, and it all goes crack when cooling to cryogenic temperatures! » 

Philippe Vallée, OMM Instrumentation Specialist, working on the instrument. On the left, he is gluing the mechanical supports on the sides of a ZnSe prism. The spectrograph is composed of 5 prisms like this one. On the right, we see him making adjustments on the H4RG detector. Photo credit: Lison Malo.

“After integrating the subsystems on the optical bench, we have to make sure that everything is in place according to the positioning tolerances provided. This is the first step,” explains Anne-Sophie Poulin-Girard, a Research Professional at COPL. “This is a critical step to ensure that the system will have the desired performance. Fortunately, we have 3D measuring machines that allow us to verify the mechanical positioning, and a range of optical tactics to validate the alignment of the various elements. »  

Since NIRPS operates in infrared light, it is crucial that it is cooled down to about -200 degrees Celsius, so that it does not itself emit light that would pollute the data. Cooling is a delicate procedure that takes almost two weeks to complete. 

The team was able to take the first images with the instrument on August 12. As the instrument is not yet on the telescope, the images did not capture the light of a star, but rather with that of calibration lamps.