Exploring Worlds with VLTI/MATISSE in the Mid-Infrared

Pushing the limits of high-angular-resolution spectroscopy, VLTI/MATISSE enables us to retrieve L- and M-band spectra of exoplanets and brown dwarfs at small angular separations (down to 100 mas), with a medium spectral resolution of R ≈ 500. In this talk, we focus on two benchmark companions: HD 72946 B, a brown dwarf, and HR 8799 e, a directly imaged exoplanet with a very low L-band flux (0.3 mJy). Observing such faint sources remains challenging, but specific post-processing tools have been developed to allow spectral extraction below the millijansky level. My research involve also optimizations and the investigation of methods improving the companion singal extraction that could be beneficial to the future ELT observation of exoplanets. The mid-IR spectral window provided by MATISSE includes molecular features such as H2O, CH4, and CO, which help constrain and refine key atmospheric parameters like the C/O ratio (giving clues of their formation mechanism), temperature, surface gravity, and vertical mixing. These physical features are all indicators of the chemistry at play in their atmospheres. In this context, we present a comparative analysis of HD 72946 B and HR 8799 e based on MATISSE observations in order to better understand the physico-chemical processes shaping their atmospheres nowadays as well as their formation mechanism long time ago.