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

Abstract

We present the 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 subtraction via di erential 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 themore » west 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 F ring.« less

Authors:
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Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1249153
Report Number(s):
LLNL-JRNL-663581-DRAFT
Journal ID: ISSN 1538-4357
Grant/Contract Number:
AC52-07NA27344
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 799; Journal Issue: 2; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS

Citation Formats

Perrin, Marshall D., Duchene, Gaspard, Millar-Blanchaer, Max, Fitzgerald, Michael P., Graham, James R., Wiktorowicz, Sloane J., Kalas, Paul G., Macintosh, Bruce, Bauman, Brian, Cardwell, Andrew, Chilcote, Jeffrey, De Rosa, Robert J., Dillon, Daren, Doyon, René, Dunn, Jennifer, Erikson, Darren, Gavel, Donald, Goodsell, Stephen, Hartung, Markus, Hibon, Pascale, Ingraham, Patrick, Kerley, Daniel, Konapacky, Quinn, Larkin, James E., Maire, Jérôme, Marchis, Franck, Marois, Christian, Mittal, Tushar, Morzinski, Katie M., Oppenheimer, B. R., Palmer, David W., Patience, Jennifer, Poyneer, Lisa, Pueyo, Laurent, Rantakyrö, Fredrik T., Sadakuni, Naru, Saddlemyer, Leslie, Savransky, Dmitry, Soummer, Rémi, Sivaramakrishnan, Anand, Song, Inseok, Thomas, Sandrine, Wallace, J. Kent, Wang, Jason J., and Wolff, Schuyler G.. Polarimetry with the Gemini Planet Imager: methods, performance at first light, and the circumstellar ring around HR 4796A. United States: N. p., 2015. Web. doi:10.1088/0004-637X/799/2/182.
Perrin, Marshall D., Duchene, Gaspard, Millar-Blanchaer, Max, Fitzgerald, Michael P., Graham, James R., Wiktorowicz, Sloane J., Kalas, Paul G., Macintosh, Bruce, Bauman, Brian, Cardwell, Andrew, Chilcote, Jeffrey, De Rosa, Robert J., Dillon, Daren, Doyon, René, Dunn, Jennifer, Erikson, Darren, Gavel, Donald, Goodsell, Stephen, Hartung, Markus, Hibon, Pascale, Ingraham, Patrick, Kerley, Daniel, Konapacky, Quinn, Larkin, James E., Maire, Jérôme, Marchis, Franck, Marois, Christian, Mittal, Tushar, Morzinski, Katie M., Oppenheimer, B. R., Palmer, David W., Patience, Jennifer, Poyneer, Lisa, Pueyo, Laurent, Rantakyrö, Fredrik T., Sadakuni, Naru, Saddlemyer, Leslie, Savransky, Dmitry, Soummer, Rémi, Sivaramakrishnan, Anand, Song, Inseok, Thomas, Sandrine, Wallace, J. Kent, Wang, Jason J., & Wolff, Schuyler G.. Polarimetry with the Gemini Planet Imager: methods, performance at first light, and the circumstellar ring around HR 4796A. United States. doi:10.1088/0004-637X/799/2/182.
Perrin, Marshall D., Duchene, Gaspard, Millar-Blanchaer, Max, Fitzgerald, Michael P., Graham, James R., Wiktorowicz, Sloane J., Kalas, Paul G., Macintosh, Bruce, Bauman, Brian, Cardwell, Andrew, Chilcote, Jeffrey, De Rosa, Robert J., Dillon, Daren, Doyon, René, Dunn, Jennifer, Erikson, Darren, Gavel, Donald, Goodsell, Stephen, Hartung, Markus, Hibon, Pascale, Ingraham, Patrick, Kerley, Daniel, Konapacky, Quinn, Larkin, James E., Maire, Jérôme, Marchis, Franck, Marois, Christian, Mittal, Tushar, Morzinski, Katie M., Oppenheimer, B. R., Palmer, David W., Patience, Jennifer, Poyneer, Lisa, Pueyo, Laurent, Rantakyrö, Fredrik T., Sadakuni, Naru, Saddlemyer, Leslie, Savransky, Dmitry, Soummer, Rémi, Sivaramakrishnan, Anand, Song, Inseok, Thomas, Sandrine, Wallace, J. Kent, Wang, Jason J., and Wolff, Schuyler G.. Wed . "Polarimetry with the Gemini Planet Imager: methods, performance at first light, and the circumstellar ring around HR 4796A". United States. doi:10.1088/0004-637X/799/2/182. https://www.osti.gov/servlets/purl/1249153.
@article{osti_1249153,
title = {Polarimetry with the Gemini Planet Imager: methods, performance at first light, and the circumstellar ring around HR 4796A},
author = {Perrin, Marshall D. and Duchene, Gaspard and Millar-Blanchaer, Max and Fitzgerald, Michael P. and Graham, James R. and Wiktorowicz, Sloane J. and Kalas, Paul G. and Macintosh, Bruce and Bauman, Brian and Cardwell, Andrew and Chilcote, Jeffrey and De Rosa, Robert J. and Dillon, Daren and Doyon, René and Dunn, Jennifer and Erikson, Darren and Gavel, Donald and Goodsell, Stephen and Hartung, Markus and Hibon, Pascale and Ingraham, Patrick and Kerley, Daniel and Konapacky, Quinn and Larkin, James E. and Maire, Jérôme and Marchis, Franck and Marois, Christian and Mittal, Tushar and Morzinski, Katie M. and Oppenheimer, B. R. and Palmer, David W. and Patience, Jennifer and Poyneer, Lisa and Pueyo, Laurent and Rantakyrö, Fredrik T. and Sadakuni, Naru and Saddlemyer, Leslie and Savransky, Dmitry and Soummer, Rémi and Sivaramakrishnan, Anand and Song, Inseok and Thomas, Sandrine and Wallace, J. Kent and Wang, Jason J. and Wolff, Schuyler G.},
abstractNote = {We present the 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 subtraction via di erential 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, 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 F ring.},
doi = {10.1088/0004-637X/799/2/182},
journal = {The Astrophysical Journal (Online)},
number = 2,
volume = 799,
place = {United States},
year = {Wed Jan 28 00:00:00 EST 2015},
month = {Wed Jan 28 00:00:00 EST 2015}
}

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  • We present the 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 priormore » 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, 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 F ring.« less
  • 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 evenmore » 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, 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
  • We present the first scattered-light image of the debris disk around HD 131835 in the H band using the Gemini Planet Imager. HD 131835 is a ∼15 Myr old A2IV star at a distance of ∼120 pc in the Sco-Cen OB association. We detect the disk only in polarized light and place an upper limit on the peak total intensity. No point sources resembling exoplanets were identified. Compared to its mid-infrared thermal emission,  in scattered light the disk shows similar orientation but different morphology. The scattered-light disk extends from ∼75 to ∼210 AU in the disk plane with roughly flatmore » surface density. Our Monte Carlo radiative transfer model can describe the observations with a model disk composed of a mixture of silicates and amorphous carbon. In addition to the obvious brightness asymmetry due to stronger forward scattering, we discover a weak brightness asymmetry along the major axis, with the northeast side being 1.3 times brighter than the southwest side at a 3σ level.« less
  • Here, we present the first scattered-light image of the debris disk around HD 131835 in the H band using the Gemini Planet Imager. HD 131835 is a ~15 Myr old A2IV star at a distance of ~120 pc in the Sco-Cen OB association. We detect the disk only in polarized light and place an upper limit on the peak total intensity. No point sources resembling exoplanets were identified. Compared to its mid-infrared thermal emission, in scattered light the disk shows similar orientation but different morphology. The scattered-light disk extends from ~75 to ~210 AU in the disk plane with roughlymore » flat surface density. Our Monte Carlo radiative transfer model can describe the observations with a model disk composed of a mixture of silicates and amorphous carbon. In addition to the obvious brightness asymmetry due to stronger forward scattering, we discover a weak brightness asymmetry along the major axis, with the northeast side being 1.3 times brighter than the southwest side at a 3σ level.« less
  • We present H- and K-band imaging polarimetry for the PDS 66 circumstellar disk obtained during the commissioning of the Gemini Planet Imager (GPI). Polarization images reveal a clear detection of the disk in to the 0.″12 inner working angle (IWA) in the H band, almost three times closer to the star than the previous Hubble Space Telescope (HST) observations with NICMOS and STIS (0.″35 effective IWA). The centro-symmetric polarization vectors confirm that the bright inner disk detection is due to circumstellar scattered light. A more diffuse disk extends to a bright outer ring centered at 80 AU. We discuss several physicalmore » mechanisms capable of producing the observed ring + gap structure. GPI data confirm enhanced scattering on the east side of the disk that is inferred to be nearer to us. We also detect a lateral asymmetry in the south possibly due to shadowing from material within the IWA. This likely corresponds to a temporally variable azimuthal asymmetry observed in HST/STIS coronagraphic imaging.« less