First on-sky results of a Fabry-Perot Instrument for Oxygen Searches (FIOS) prototype

Context. The upcoming Extremely Large Telescopes (ELTs) are expected to have a sufficient collecting area required to detect potential biosignature gases such as molecular oxygen, O₂, in the atmosphere of terrestrial planets around nearby stars.
Aims: One of the most promising detection methods is transmission spectroscopy. To maximize our capability to detect O₂ using this method, spectral resolutions R ≥ 300 000 are required to fully resolve the absorption lines in an Earth-like exoplanet atmosphere and disentangle the signal from telluric lines.
Methods: Current high-resolution spectrographs typically achieve a spectral resolution of R ~ 100 000. Increasing the resolution in seeing limited observations and/or instruments requires drastically larger optical components, making these instruments even more expensive and hard to fabricate and assemble. Instead, we demonstrate a new approach to high-resolution spectroscopy. We implemented an ultra-high spectral resolution booster to be coupled to a high-resolution spectrograph. The instrument is based on a chained Fabry-Perot array which generates a hyperfine spectral profile.
Results: We present on-sky telluric observations with a lab demonstrator. Depending on the configuration, this two-arm prototype reaches a resolution of R = 250 000-350 000. After carefully modeling the prototype's behavior, we propose a Fabry-Perot Interferometer (FPI) design for an eight-arm array configuration aimed at ELTs capable of exceeding R = 300 000.
Conclusions: The novel FPI resolution booster can be plugged in at the front end of an existing R = 100 000 spectrograph to overwrite the spectral profile with a higher resolution for exoplanet atmosphere studies.