The upcoming Extremely Large Telescopes (ELTs) are expected to have the collecting area required to detect potential biosignature gases in the atmosphere of rocky planets around nearby low-mass stars. Some efforts are currently focusing on searching for molecular oxygen (O2), since O2 is a known biosignature on Earth. One of the most promising methods to search for O2 is transmission spectroscopy in which high-resolution spectroscopy is combined with cross-correlation techniques. In this method, high spectral resolution is required both to resolve the exoplanet’s O2 lines and to separate them from foreground telluric absorption. While current astronomical spectrographs typically achieve a spectral resolution of 100,000, recent studies show that resolutions of 300,000 – 400,000 are optimal to detect O2 in the atmosphere of earth analogs with the ELTs. Fabry Perot Interferometer (FPI) arrays have been proposed as a relatively low-cost way to reach these resolutions. In this paper, we present performance results for our 2-FPI array lab prototype, which reaches a resolving power of 600,000. We further discuss the use of multi-cavity etalons (dualons) to be resolution boosters for existing spectrographs.
We report on the status of The Tierras Observatory at the F.L. Whipple Observatory atop Mt. Hopkins, Arizona, a refurbished 1.3-m ultra-precise fully-automated photometer. Tierras is designed to regularly achieve photometric precisions below 700 ppm from the ground, which will enable the characterization of terrestrial planet transits orbiting < 0.3R stars with 3σ significance, as well as the potential discovery of exo-moons and exo-rings. The design choices that will enable our science goals include: a four-lens focal reducer and field-flattener to increase the field-of-view of the telescope from a 11.94' to a 0.48‡ side; a custom narrow bandpass (40.2 nm FWHM) filter centered around 863.5 nm to minimize precipitable water vapor (PWV) errors known to limit ground-based photometry of red dwarfs; and a deep-depletion 4K x 4K CCD with a 300ke- full well and QE< 85% in our bandpass, operating in frame transfer mode. We are also pursuing the design⊚ of a set of baffes to minimize the significant amount of scattered light currently reaching the image plane. Tierras will begin science operations in early 2021.
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