The Tierras Observatory: An ultra-precise photometer to characterize nearby terrestrial exoplanets

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.