Multiband Polarimetric Imaging of HR 4796A with the Gemini Planet Imager

Creators: Arriaga, Pauline; Fitzgerald, Michael P.; Duchêne, Gaspard; Kalas, Paul; Millar-Blanchaer, Maxwell A.; Perrin, Marshall D.; Chen, Christine H.; Mazoyer, Johan; Ammons, Mark; Bailey, Vanessa P.; Barman, Trafis S.; Bulger, Joanna; Chilcote, Jeffrey K.; Cotten, Tara; De Rosa, Robert J.; Doyon, Rene; Esposito, Thomas M.; Follette, Katherine B.; Gerard, Benjamin L.; Goodsell, Stephen; Graham, James R.; Greenbaum, Alexandra Z.; Hibon, Pascale; Hom, Justin; Hung, Li-Wei; Ingraham, Patrick; Konopacky, Quinn M.; Macintosh, Bruce A.; Maire, Jérôme; Marchis, Franck; Marley, Mark S.; Marois, Christian; Metchev, Stanimir; Nielsen, Eric L.; Oppenheimer, Rebecca; Palmer, David W.; Patience, Jenny; Poyneer, Lisa A.; Pueyo, Laurent; Rajan, Abhijith; Rameau, Julien; Rantakyrö, Fredrik T.; Ruffio, Jean-Baptiste; Savransky, Dmitry; Schneider, Adam C.; Sivaramakrishnan, Anand; Song, Inseok; Soummer, Remi; Thomas, Sandrine; Wang, Jason J.; Ward-Duong, Kimberly; Wolff, Schuyler G.

Abstract

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.

Additional Information

© 2020. The American Astronomical Society. Received 2020 March 10; revised 2020 April 28; accepted 2020 May 8; published 2020 July 23. This research was supported in part by NSF AST-1413718 and AST-1615272, AST-NNX15AC89G, AST-1413718, AST-1615272. J.M. acknowledges support for this work provided by NASA through the NASA Hubble Fellowship grant #HST-HF2-51414.001, awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. Portions of this work were performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. This work is based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc. (AURA), under a cooperative agreement with the National Science Foundation (NSF) on behalf of the Gemini partnership: the NSF (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina), and Ministério da Ciência, Tecnologia e Inovação (Brazil). This work was supported by the NSF AST-1518332 (T.M.E., R.J.D.R., J.R.G., P.K., G.D.) and NASA grants NNX15AC89G and NNX15AD95G/NExSS (T.M.E., B.M., R.J.D.R., G.D., J.J.W, J.R.G., P.K.). This work benefited from NASA's Nexus for Exoplanet System Science (NExSS) research coordination network, sponsored by NASA's Science Mission Directorate. G.D. acknowledges support from NSF grants AST-141378 and AST-1518332, as well as NASA grants NNX15AC89G and NNX15AD95G/NExSS. Software: Gemini Planet Imager Data Pipeline (Perrin et al. 2014), PyKLIP (Wang et al. 2014), MCFOST (Pinte et al. 2006a), emcee (Foreman-Mackey et al. 2013).

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