Juliana García-Mejía, David Charbonneau, Dan Fabricant, Jonathan Irwin, Robert Fata, Joseph Zajac, Brian McLeod, Peter Doherty, Ryan Cloutier Tierras the Observatory First Light Results from a New Ultra- precise Time-series M-dwarf Photometer For more information, contact: juliana.garcia-mejia@cfa.harvard.edu State-of-the-art ground-based robotic facilities studying mid-to-late M dwarfs and their planets typically reach per-point night-to-night photometric precisions in the order of 3000 ppm. These experiments are limited by precipitable water vapor (PWV) error, since water features in the photometric bandpass result in a color dependent offset when comparing the relative brightness of the red target to the blue field stars. We have refashioned the 1.3-m 2MASS N 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 (1) limit systematic errors, notably PWV error, to <250 ppm across an observing season and (2) limit stochastic errors, notably scintillation and target photon noise, to less than that of an Earth-transit for a 5 min integration time, for all stars with radii <0.3 R⊙ out to a distance of 15 pc. For more information, please refer to Garcia-Mejia et al. Proc. of the SPIE, 114457R, arXiv:2012.09744, (2020). Science Operations Have Begun! A Representative First-Light Tierras Light Curve Secondary Baffle 1 3 820 830 840 850 860 870 880 890 900 910 Wavelength (nm) 0 20 40 60 80 100 Transmission (%) Tellurics, 5mm Filter (Empirical) A four-lens focal reducer and field-flattener under the 1.3-m primary mirror (M1), which increases the field of view from a to a side and allows us to monitor more comparison stars. 0.19∘ 0.50∘ A custom narrow (40.2 nm FWHM) bandpass filter centered at 863.5 nm (right plot) avoids prominent telluric features and desensitizes our o b s e r v a t i o n s f r o m changes in PWV. 400 600 800 1000 Wavelength (nm) 0.0 0.2 0.4 0.6 0.8 Quantum E±ciency Tierras CCD MEarth CCD Summer 2021: Installed the Tierras filter, optics, and CCD dewar under M1 (top left). Fall 2021: Tested the remote control software on- s k y , c o l l i m a t e d t h e telescope, and reached first light! Winter 2021-2022: Built and installed a new set of baffles to minimize sky background (bottom right). On the left, we show a schematic diagram of the optics, along with representative ray traces and spot diagrams. Plate scale = 0.43’’/pixel. 2 A deep- d e p l e t i o n C C D operating in fast f r a m e t r a n s f e r (shutter-less) mode with>85% quantum efficiency (QE) in our bandpass (right plot), low read-noise and low dark current. A custom dewar houses the CCD, maintaining it at -105℃. 4K × 4K Commissioning Summary CCD Dewar Mount Plate Optics Installation Fixture Mount Surface Filter mounted to its bezel CCD chip with masked readout regions Primary Baffle Primary Mirror LHS 2913 - M3 star 13 pc away. This light curve (left) is not de-trended, highlighting the efficacy of our filter. We are already meeting our photometric precision goals on this star (right). Project Overview LHS 2913 The design choices enabling our photometric precision goals include: