Spectral resolution is one of the key instrument parameters for a future flagship mission aiming to detect and characterize rocky exoplanets. At visible wavelengths, the relatively narrow molecular oxygen A-band absorption feature at 760 nm is one of the driving spectrograph design considerations. We combined numerical models for a segmented space telescope, coronagraph, and lenslet array integral field spectrograph to simulate high-fidelity data products for an Earth-analog exoplanet observed in a 20% bandpass centered on this absorption feature. The simulations were repeated over a set of spectral resolutions, integration times, and noise realizations. The extracted planet spectra were fed into a Bayesian spectral retrieval pipeline. Our nested sampling forward model interpolates over a 6-parameter grid of terrestrial reflectance spectra. For a signal-to-noise ratio per spectral bin of 15, we find modest constraints on the O2 atmosphere mixing ratio are possible at spectral resolutions R<110, with [16th , 84th] percentile confidence interval [∼ 5%, ∼ 40%] given a true input mixing ratio of 21%. At higher spectral resolutions, for a fixed integration time we find no significant improvement in the confidence interval of the O2 mixing ratio.
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