High-resolution Spectroscopy Using Fabry–Perot Interferometer Arrays: An Application to Searches for O2 in Exoplanetary Atmospheres

We present a novel implementation for extremely high-resolution spectroscopy using custom-designed Fabry–Perot Interferometer (FPI) arrays. For a given telescope aperture at the seeing-limited case, these arrays can achieve resolutions well in excess of R ∼ 10 5 using optical elements that are orders of magnitude smaller in size than standard echelle spectrographs of similar resolution. We apply this method specifically to the search for O 2 in exoplanetary atmospheres using the O 2 A band at 0.76 μ m and show how an FPI array composed of ∼10 etalons with parameters optimized for this science case can record R = 3–5 × 10 5 spectra covering the full O 2 A band. Using simulated observations of the atmosphere of a transiting nearby Earth-like planet, we show how observations with an FPI array coupled to a long-slit spectrograph can reduce the number of transit observations needed to produce a 3 σ detection of O 2 by ∼30% compared to observations with an R = 10 5 echelle spectrograph. This in turn leads to a decrease in an observing program duration of several years. The number of transits needed for a 3 σ detection can be further reduced by increasing the efficiency of FPI arrays using dualons (an etalon with a buried reflective layer) and by coupling the FPI array to a dedicated spectrograph optimized for the O 2 A band.