Polarimetry with the gemini planet imager: Methods, performance at first light, and the circumstellar ring around HR 4796A

Marshall D. Perrin, Gaspard Duchene, Max Millar-Blanchaer, Michael P. Fitzgerald, James R. Graham, Sloane J. Wiktorowicz, Paul G. Kalas, Bruce Macintosh, Brian Bauman, Andrew Cardwell, Jeffrey Chilcote, Robert J. De Rosa, Daren Dillon, René Doyon, Jennifer Dunn, Darren Erikson, Donald Gavel, Stephen Goodsell, Markus Hartung, Pascale HibonPatrick Ingraham, Daniel Kerley, Quinn Konapacky, James E. Larkin, Jérôme Maire, Franck Marchis, Christian Marois, Tushar Mittal, Katie M. Morzinski, B. R. Oppenheimer, David W. Palmer, Jennifer Patience, Lisa Poyneer, Laurent Pueyo, Fredrik T. Rantakyrö, Naru Sadakuni, Leslie Saddlemyer, Dmitry Savransky, Rémi Soummer, Anand Sivaramakrishnan, Inseok Song, Sandrine Thomas, J. Kent Wallace, Jason J. Wang, Schuyler G. Wolff

Research output: Contribution to journalArticle

64 Scopus citations

Abstract

We present the first results from the polarimetry mode of the Gemini Planet Imager (GPI), which uses anew 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 thewest side, and the ring must be slightly optically thick in order to explain the lower brightness in total intensity there. These findings suggest that the ring is geometrically narrow and dynamically cold, perhaps shepherded by larger bodies in the same manner as Saturn's Fring.

Original languageEnglish (US)
Article number182
JournalAstrophysical Journal
Volume799
Issue number2
DOIs
StatePublished - Feb 1 2015

Keywords

  • Circumstellar matter
  • Instrumentation: adaptive optics
  • Instrumentation: high angular resolution
  • Instrumentation: polarimeters
  • Polarization
  • Stars: individual (HR 4796A)

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Perrin, M. D., Duchene, G., Millar-Blanchaer, M., Fitzgerald, M. P., Graham, J. R., Wiktorowicz, S. J., Kalas, P. G., Macintosh, B., Bauman, B., Cardwell, A., Chilcote, J., De Rosa, R. J., Dillon, D., Doyon, R., Dunn, J., Erikson, D., Gavel, D., Goodsell, S., Hartung, M., ... Wolff, S. G. (2015). Polarimetry with the gemini planet imager: Methods, performance at first light, and the circumstellar ring around HR 4796A. Astrophysical Journal, 799(2), [182]. https://doi.org/10.1088/0004-637X/799/2/182