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

Abstract

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.