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Title: The orbit and transit prospects for β pictoris b constrained with one milliarcsecond astrometry

A principal scientific goal of the Gemini Planet Imager (GPI) is obtaining milliarcsecond astrometry to constrain exoplanet orbits. However, astrometry of directly imaged exoplanets is subject to biases, systematic errors, and speckle noise. Here, we describe an analytical procedure to forward model the signal of an exoplanet that accounts for both the observing strategy (angular and spectral differential imaging) and the data reduction method (Karhunen–Loève Image Projection algorithm). We use this forward model to measure the position of an exoplanet in a Bayesian framework employing Gaussian processes and Markov-chain Monte Carlo to account for correlated noise. In the case of GPI data on β Pic b, this technique, which we call Bayesian KLIP-FM Astrometry (BKA), outperforms previous techniques and yields 1σ errors at or below the one milliarcsecond level. We validate BKA by fitting a Keplerian orbit to 12 GPI observations along with previous astrometry from other instruments. The statistical properties of the residuals confirm that BKA is accurate and correctly estimates astrometric errors. Our constraints on the orbit of β Pic b firmly rule out the possibility of a transit of the planet at 10-σ significance. However, we confirm that the Hill sphere of β Pic b will transit,more » giving us a rare chance to probe the circumplanetary environment of a young, evolving exoplanet. As a result, we provide an ephemeris for photometric monitoring of the Hill sphere transit event, which will begin at the start of April in 2017 and finish at the end of January in 2018.« less
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  1. Univ. of California, Berkeley, CA (United States)
  2. Space Telescope Science Institute, Baltimore, MD (United States)
  3. Univ. of Toronto, Toronto, ON (Canada)
  4. Stanford Univ., Stanford, CA (United States)
  5. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  6. Univ. of California, Los Angeles, CA (United States)
  7. Univ. of Arizona, Tucson, AZ (United States)
  8. Subaru Telescope, Hilo, HI (United States)
  9. Princeton Univ., Princeton, NJ (United States)
  10. Gemini Observatory, La Serena (Chile); Large Binocular Telescope Observatory, Tucson, AZ (United States)
  11. Univ. of Georgia, Athens, GA (United States)
  12. Univ. de Montreal, Montreal, QC (Canada)
  13. Univ. of California, Berkeley, CA (United States); Univ. Grenoble Alpes/CNRS, Grenoble (France)
  14. Space Telescope Science Institute, Baltimore, MD (United States); Johns Hopkins Univ., Baltimore, MD (United States)
  15. European Southern Observatory, Santiago (Chile)
  16. Large Synoptic Survey Telescope, Tucson, AZ (United States)
  17. Univ. of California, San Diego, La Jolla, CA (United States)
  18. SETI Institute, Mountain View, CA (United States)
  19. NASA Ames Research Center (ARC), Moffett Field, CA (United States)
  20. National Research Council of Canada Herzberg, Victoria, BC (Canada); Univ. of Victoria, Victoria, BC (Canada)
  21. The Univ. of Western Ontario, London, ON (Canada); Stony Brook Univ., Stony Brook, NY (United States)
  22. Stanford Univ., Stanford, CA (United States); SETI Institute, Mountain View, CA (United States)
  23. American Museum of Natural History, New York, NY (United States)
  24. California Inst. of Technology (CalTech), Pasadena, CA (United States)
  25. Arizona State Univ., Tempe, AZ (United States)
  26. Univ. of Montreal, Montreal, QC (Canada)
  27. Cornell Univ., Ithaca, NY (United States)
  28. The Aerospace Corp., El Segundo, CA (United States)
Publication Date:
Report Number(s):
Journal ID: ISSN 1538-3881; TRN: US1701584
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Astronomical Journal (Online)
Additional Journal Information:
Journal Name: Astronomical Journal (Online); Journal Volume: 152; Journal Issue: 4; Journal ID: ISSN 1538-3881
IOP Publishing
Research Org:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org:
Country of Publication:
United States
79 ASTRONOMY AND ASTROPHYSICS; astrometry; planets and satellites: individual (βPictoris b); techniques: image processing
OSTI Identifier: