Toward Space-like Photometric Precision from the Ground with Beam-shaping Diffusers

Creators: Stefansson, Gudmundur; Mahadevan, Suvrath; Hebb, Leslie; Wisniewski, John P.; Huehnerhoff, Joseph; Morris, Brett; Halverson, Sam; Zhao, Ming; Wright, Jason; O'Rourke, Joseph G.; Knutson, Heather; Hawley, Suzanne; Kanodia, Shubham; Li, Yiting; Hagen, Lea M. Z.; Liu, Leo J.; Beatty, Thomas G.; Bender, Chad F.; Robertson, Paul; Dembicky, Jack; Gray, Candace; Ketzeback, William; McMillan, Russet; Rudyk, Theodore

Abstract

We demonstrate a path to hitherto unachievable differential photometric precisions from the ground, both in the optical and near-infrared (NIR), using custom-fabricated beam-shaping diffusers produced using specialized nanofabrication techniques. Such diffusers mold the focal plane image of a star into a broad and stable top-hat shape, minimizing photometric errors due to non-uniform pixel response, atmospheric seeing effects, imperfect guiding, and telescope-induced variable aberrations seen in defocusing. This PSF reshaping significantly increases the achievable dynamic range of our observations, increasing our observing efficiency and thus better averages over scintillation. Diffusers work in both collimated and converging beams. We present diffuser-assisted optical observations demonstrating 62_(-16)^(+26) ppm precision in 30 minute bins on a nearby bright star 16 Cygni A (V = 5.95) using the ARC 3.5 m telescope—within a factor of ~2 of Kepler's photometric precision on the same star. We also show a transit of WASP-85-Ab (V = 11.2) and TRES-3b (V = 12.4), where the residuals bin down to 180_(-41)^(+66) ppm in 30 minute bins for WASP-85-Ab—a factor of ~4 of the precision achieved by the K2 mission on this target—and to 101 ppm for TRES-3b. In the NIR, where diffusers may provide even more significant improvements over the current state of the art, our preliminary tests demonstrated 137_(-36)^(+64) ppm precision for a K_S = 10.8 star on the 200 inch Hale Telescope. These photometric precisions match or surpass the expected photometric precisions of TESS for the same magnitude range. This technology is inexpensive, scalable, easily adaptable, and can have an important and immediate impact on the observations of transits and secondary eclipses of exoplanets.

Additional Information

© 2017 American Astronomical Society. Received 2017 April 28. Accepted 2017 August 22. Published 2017 October 5. We thank the anonymous referee for a thoughtful reading of the manuscript, and for useful suggestions and comments. We gratefully acknowledge the work and assistance of Tasso Sales and Laura Weller-Brophy at RPC Photonics, without whose help this project would not have been possible. G.K.S. wishes to thank Eric Ford for helpful discussions on MCMC fitting and inference. This work was directly seeded and supported by a Scialog grant from the Research Corporation for Science Advancement (Rescorp) to S.M., L.H., and J.W. This work was partially supported by funding from the Center for Exoplanets and Habitable Worlds. The Center for Exoplanets and Habitable Worlds is supported by the Pennsylvania State University, the Eberly College of Science, and the Pennsylvania Space Grant Consortium. G.K.S. acknowledges support from the Leifur Eiriksson Foundation Scholarship. This work was supported by NASA Headquarters under the NASA Earth and Space Science Fellowship Program Grant NNX16AO28H. This work was performed in part under contract with the Jet Propulsion Laboratory (JPL) funded by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute. We acknowledge support from NSF grants AST-1006676, AST-1126413, AST-1310885, and AST-1517592, the NASA Astrobiology Institute (NAI; NNA09DA76A), and PSARC. These results are based on observations obtained with the Apache Point Observatory 3.5 m telescope which is owned and operated by the Astrophysical Research Consortium, the Hale 200 inch Telescope at Palomar Observatory, and the Planewave CDK 24 Telescope operated by the Penn State Department of Astronomy & Astrophysics at Davey Lab Observatory. The Palomar Hale 200 inch telescope is operated by Caltech and the Jet Propulsion Laboratory. This paper includes data collected by the Kepler telescope. The Kepler and K2 data presented in this paper were obtained from the Mikulski Archive for Space Telescopes (MAST). The Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX09AF08G and by other grants and contracts. Funding for the K2 Mission is provided by the NASA Science Mission directorate. This research made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. Facilities: A - RC, Hale, DAVEY:0.6m, Kepler. Software: AstroImageJ (Collins et al. 2017), astropy (Astropy Collaboration et al. 2013), astroscrappy, BATMAN (Kreidberg 2015), corner.py (Foreman-Mackey 2016), emcee (Foreman-Mackey et al. 2013), Everest 2.0 (Luger et al. 2017), EXOFAST (Eastman et al. 2013), MC3 (Cubillos et al. 2017), TERRASPEC (Bender et al. 2012), Zemax OpticStudio.

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