Extreme precision photometry from the ground with beam-shaping diffusers for K2, TESS, and beyond

Gudmundur Stefansson, Suvrath Mahadevan, John Wisniewski, Yiting Li, Leslie Hebb, Brett Morris, Samuel Halverson, Andrew Monson, Paul Robertson

Research output: Chapter in Book/Report/Conference proceedingConference contribution

9 Scopus citations


The Transiting Exoplanet Survey Satellite (TESS, launched early 2018) is expected to find a multitude of new transiting planet candidates around the nearest and brightest stars. Timely high-precision follow-up observations from the ground are essential in confirming and further characterizing the planet candidates that TESS will find. However, achieving extreme photometric precisions from the ground is challenging, as ground-based telescopes are subject to numerous deleterious atmospheric effects. Beam-shaping diffusers are emerging as a low-cost technology to achieve hitherto unachievable differential photometric precisions from the ground. These 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. In this paper, we expand on our previous work (Stefansson et al. 2017; Stefansson et al. 2018), providing a further detailed discussion of key guidelines when sizing a diffuser for use on a telescope. Furthermore, we present our open source Python package iDiffuse which can calculate the expected PSF size of a diffuser in a telescope system, along with its expected on-sky diffuser-assisted photometric precision for a host star of a given magnitude. We use iDiffuse to show that most (∼80%) of the planet hosts that TESS will find will be scintillation limited in transit observations from the ground. Although iDiffuse has primarily been developed to plan challenging transit observations using the diffuser on the ARCTIC imager on the ARC 3.5m Telescope at Apache Point observatory, iDiffuse is modular and can be easily extended to calculate the expected diffuser-assisted photometric precisions on other telescopes.

Original languageEnglish (US)
Title of host publicationGround-based and Airborne Instrumentation for Astronomy VII
EditorsLuc Simard, Luc Simard, Christopher J. Evans, Hideki Takami
ISBN (Print)9781510619579
StatePublished - 2018
EventGround-based and Airborne Instrumentation for Astronomy VII 2018 - Austin, United States
Duration: Jun 10 2018Jun 14 2018

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X


OtherGround-based and Airborne Instrumentation for Astronomy VII 2018
Country/TerritoryUnited States

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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