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Multiband polarimetric imaging of HR 4796A with the Gemini Planet Imager.

Arriaga, Pauline and Fitzgerald, Michael P. and Duchêne, Gaspard and Kalas, Paul and Millar-Blanchaer, Maxwell A. and Perrin, Marshall D. and Chen, Christine H. and Mazoyer, Johan and Ammons, Mark and Bailey, Vanessa P. and Barman, Trafis S. and Bulger, Joanna and Chilcote, Jeffrey K. and Cotten, Tara and De Rosa, Robert J. and Doyon, Rene and Esposito, Thomas M. and Follette, Katherine B. and Gerard, Benjamin L. and Goodsell, Stephen and Graham, James R. and Greenbaum, Alexandra Z. and Hibon, Pascale and Hom, Justin and Hung, Li-Wei and Ingraham, Patrick and Konopacky, Quinn M. and Macintosh, Bruce A. and Maire, Jérôme and Marchis, Franck and Marley, Mark S. and Marois, Christian and Metchev, Stanimir and Nielsen, Eric L. and Oppenheimer, Rebecca and Palmer, David W. and Patience, Jenny and Poyneer, Lisa A. and Pueyo, Laurent and Rajan, Abhijith and Rameau, Julien and Rantakyrö, Fredrik T. and Ruffio, Jean-Baptiste and Savransky, Dmitry and Schneider, Adam C. and Sivaramakrishnan, Anand and Song, Inseok and Soummer, Remi and Thomas, Sandrine and Wang, Jason J. and Ward-Duong, Kimberly and Wolff, Schuyler G. (2020) 'Multiband polarimetric imaging of HR 4796A with the Gemini Planet Imager.', Astronomical journal., 160 (2). p. 79.


HR4796A hosts a well-studied debris disk with a long history due to its high fractional luminosity and favorable inclination, which facilitate both unresolved and resolved observations. We present new J- and K 1-band images of the resolved debris disk HR4796A taken in the polarimetric mode of the Gemini Planet Imager (GPI). The polarized intensity features a strongly forward-scattered brightness distribution and is undetected at the far side of the disk. The total intensity is detected at all scattering angles and also exhibits a strong forward-scattering peak. We use a forward-modeled geometric disk in order to extract geometric parameters, polarized fraction, and total intensity scattering phase functions for these data as well as H-band data previously taken by GPI. We find the polarized phase function becomes increasingly more forward-scattering as wavelength increases. We fit Mie and distribution of hollow spheres (DHS) grain models to the extracted functions. We find that it is possible to generate a satisfactory model for the total intensity using a DHS model, but not with a Mie model. We find that no single grain population of DHS or Mie grains of arbitrary composition can simultaneously reproduce the polarized fraction and total intensity scattering phase functions, indicating the need for more sophisticated grain models.

Item Type:Article
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Publisher statement:© 2020. The American Astronomical Society. All rights reserved.
Date accepted:08 May 2020
Date deposited:12 August 2020
Date of first online publication:23 July 2020
Date first made open access:12 August 2020

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