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Title: Polarimetry with the Gemini Planet Imager. Methods, performance at first light, and the circumstellar ring around HR 4796A

We report he first results from the polarimetry mode of the Gemini Planet Imager (GPI), which uses a new integral field polarimetry architecture to provide high contrast linear polarimetry with minimal systematic biases between the orthogonal polarizations. We describe the design, data reduction methods, and performance of polarimetry with GPI. Point-spread function (PSF) subtraction via differential polarimetry suppresses unpolarized starlight by a factor of over 100, and provides sensitivity to circumstellar dust reaching the photon noise limit for these observations. In the case of the circumstellar disk around HR 4796A, GPI’s advanced adaptive optics system reveals the disk clearly even prior to PSF subtraction. In polarized light, the disk is seen all the way in to its semi-minor axis for the first time. The disk exhibits surprisingly strong asymmetry in polarized intensity, with the west side ≳9 times brighter than the east side despite the fact that the east side is slightly brighter in total intensity. Based on a synthesis of the total and polarized intensities, we now believe that the west side is closer to us, contrary to most prior interpretations. Forward scattering by relatively large silicate dust particles leads to the strong polarized intensity on the west side,more » and the ring must be slightly optically thick in order to explain the lower brightness in total intensity there. In conclusion, these findings suggest that the ring is geometrically narrow and dynamically cold, perhaps shepherded by larger bodies in the same manner as Saturn’s F ring.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [5] ;  [7] ;  [8] ;  [9] ;  [4] ;  [10] ;  [6] ;  [11] ;  [12] ;  [12] ;  [6] ;  [9] ;  [9] ;  [9] more »;  [13] ;  [12] ;  [3] ;  [4] ;  [3] ;  [14] ;  [12] ;  [5] ;  [15] ;  [16] ;  [8] ;  [17] ;  [8] ;  [1] ;  [9] ;  [9] ;  [12] ;  [18] ;  [1] ;  [1] ;  [19] ;  [20] ;  [21] ;  [5] ;  [22] « less
  1. Space Telescope Science Institute, Baltimore, MD (United States)
  2. Univ. of California, Berkeley, CA (United States); Univ. Grenoble Alpes, Grenoble (France); CNRS, Institut de Planetologie et d'Astrophysique de Grenoble, Grenoble (France)
  3. Univ. of Toronto, ON (Canada)
  4. Univ. of California (UCLA), Los Angeles, CA (United States)
  5. Univ. of California, Berkeley, CA (United States)
  6. Univ. of California, Santa Cruz, CA (United States)
  7. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Stanford Univ., CA (United States). Kavli Institute for Particle Astrophysics and Cosmology
  8. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  9. Gemini Observatory, La Serena (Chile)
  10. Arizona State Univ., Tempe, AZ (United States). School of Earth and Space Exploration; Univ. of Exeter, Exeter (United Kingdom)
  11. Univ. of Montreal, Quebec (Canada)
  12. National Research Council of Canada Herzberg, Victoria, BC (Canada)
  13. Stanford Univ., CA (United States). Kavli Institute for Particle Astrophysics and Cosmology; Univ. of Montreal, Quebec (Canada)
  14. SETI Inst., Mountain View, CA (United States). Carl Sagan Center
  15. Univ. of Arizona, Tucson, AZ (United States)
  16. American Museum of Natural History (AMNH), New York, NY (United States)
  17. Arizona State Univ., Tempe, AZ (United States). School of Earth and Space Exploration
  18. Cornell Univ., Ithaca, NY (United States). Sibley School of Mechanical and Aerospace Engineering
  19. Univ. of Georgia, Athens, GA (United States)
  20. NASA Ames Research Center (ARC), Moffett Field, Mountain View, CA (United States)
  21. California Inst. of Technology (CalTech), Pasadena, CA (United States). Jet Propulsion Lab.
  22. Space Telescope Science Institute, Baltimore, MD (United States); Johns Hopkins Univ., Baltimore, MD (United States). Department of Physics and Astronomy
Publication Date:
OSTI Identifier:
1253148
Grant/Contract Number:
AC52-07NA27344
Type:
Accepted Manuscript
Journal Name:
The Astrophysical Journal
Additional Journal Information:
Journal Volume: 799; Journal Issue: 2; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Research Org:
Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; 47 OTHER INSTRUMENTATION circumstellar matter; instrumentation: adaptive optics; instrumentation; high angular resolution; instrumentation: polarimeters; polarization; stars; individual (HR 4796A)