First Light Results from the Tierras Observatory, An Ultra-precise Time-series M-dwarf Photometer

We are engaged in a project to refashion the 1.3m 2MASS telescope located at the F.L. Whipple Observatory atop Mount Hopkins, Arizona, into an ultra-precise time-series photometer: The Tierras Observatory is designed to achieve a photometric precision of 250 ppm across an observing season. The design choices that enable this precision include a four-lens focal reducer and field-flattener to increase the field-of-view of the telescope from 12 arc minutes to 0.48 degrees on a side; a custom narrow (40 nm) bandpass filter centered around 863.5 nm to minimize precipitable water vapor errors known to limit ground-based photometry of M dwarfs; a deep-depletion 4k × 4k CCD with a quantum efficiency of 85% in our bandpass, operating in frame transfer mode; and, a fully automated observing mode. Tierras achieved first light in the fall of 2021, and in February 2022 we installed a new set of baffles to significantly reduce sky background. We will share recent light curves and summarize our current on-sky performance. Tierras is starting a three-year survey of M dwarf stars within 15 parsecs to detect new terrestrial planets that were too small or too cool to be found by TESS or previous ground-based efforts, and to monitor known exoplanets (both rocky and gaseous) to search for satellites or systems of circumstellar rings. Furthermore, a long term monitoring campaign will permit Tierras to determine M dwarf rotation periods, elucidating the process and timescale over which these stars lose their angular momentum.