The Tierras Observatory: An Ultra-precise Photometer To Characterize Nearby Terrestrial Exoplanets


The lens alignment and bonding process for lens 1 (BSM51Y) inside our clean room. Top left: polished and coated lens sitting above its delivery casing bottom. After removing the lens from its casing, we cleaned and primed its edge with MOMENTIVE SS4155 blue primer. Top right: lens sitting on top of the TRIOPTICS Opticentric highprecision lens centration and alignment machine’s tilt/translation table (blue and black circular surfaces below lens). Note the lens sits inside a black delrin bond ring and interfaces to the Opticentric table via custom aluminum fixturing. The delrin ring is meant to prevent liquid RTV spillage during bonding. Bottom left: cleaned and primed bezel sits above the lens and is independently supported by three fine adjustment centration and tilt blocks. The blocks are isolated from the Opticentric tilt/translation table to enable independent bezel and lens alignment. In subsequent steps, the bezel is carefully lowered and positioned optimally with respect to the lens vertex in order to fulfill our optical prescription and axial displacement/centration/tilt tolerances. Bottom right: After the lens and bezel are optimally positioned with respect to each other, we deposit MOMENTIVE RTV560 (red liquid rubber) between the lens edge and the bezel to bond them together.

We report on the status of the Tierras Observatory, a refurbished 1.3-m ultra-precise fully-automated photometer located at the F. L. Whipple Observatory atop Mt. Hopkins, Arizona.

Tierras is designed to limit systematic errors, notably precipitable water vapor (PWV), to 250 ppm, enabling the characterization of terrestrial planet transits orbiting <0.3R⊙ stars, 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 PWV errors known to limit ground-based photometry of red dwarfs; and a deep-depletion 4K×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 baffles to minimize the significant amount of scattered light reaching the image plane. Tierras will begin science operations in early 2021.

Juliana García-Mejía, David Charbonneau, Daniel Fabricant, Jonathan M. Irwin, Robert Fata, Joseph M. Zajac, Peter E. Doherty

Comments: SPIE Astronomical Telescopes & Instrumentation 2020 Proceedings (11445-168), 20 pages, 11 figures
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2012.09744 [astro-ph.IM] (or arXiv:2012.09744v1 [astro-ph.IM] for this version)
Submission history
From: Juliana García-Mejía
[v1] Thu, 17 Dec 2020 17:02:17 UTC (8,360 KB)
https://arxiv.org/abs/2012.09744
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