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Into the red: opening up the M-band for high resolution spectroscopic characterisation of exoplanet atmospheres

Presentation #503.01 in the session The Future.

Published onApr 03, 2024
Into the red: opening up the M-band for high resolution spectroscopic characterisation of exoplanet atmospheres

High resolution spectroscopy (HRS; R~100,000) combined with adaptive optics has been enormously successful in advancing our knowledge of exoplanet atmospheres, from chemistry to rotation and atmospheric dynamics. It now a major science driver for the Extremely Large Telescopes (ELTs), including the search for biosignatures in the nearest rocky exoplanet atmospheres with first-light instruments, such as METIS/ELT. METIS will operate at 3-5 μm, which contains spectral features of key biosignature molecules such as CO2, H2O, and CH4. However, HRS is untested beyond 3.3 μm, where the thermal background becomes a significant challenge. Here, we open up the M-band (4-5 μm) for the first time to HRS. We present CRIRES+/VLT R = 100,00 M-band observations of the young giant exoplanet beta Pic b, and successfully detect CO (S/N=7) in its atmosphere at 4.75 μm. We further measure the planet spin rate and discuss other molecules, including silicates, which have spectral features in the M-band and act as tracers of the rock/vapour accretion history of giant exoplanets. The opening of the M-band to HRS therefore offers a new regime of exploration, and we highlight how the superior spatial and spectral resolution, collecting area, and the resulting reduced thermal background of the ELT will allow HRS to push to the characterisation of rocky exoplanets, from lava worlds to habitable zone planets.

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