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 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, 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.

27 pages, 16 figures, submitted to the Astrophysical Journal. A version with full resolution figures is available at http://www.stsci.edu/~mperrin/papers/gpi_polarimetry_and_HR_4796A.pdf

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• Monte Carlo radiative transfer in protoplanetary disks
• Placing Confidence Limits on Polarization Measurements
• STIS Imaging of the HR 4796A Circumstellar Debris Ring
• Grain Alignment by Radiative Torques in Special Conditions and Implications
• Outer edges of debris discs: how sharp is sharp?
• Astrometry and Photometry with Coronagraphs
• Speckle Suppression Through Dual Imaging Polarimetry, and a Ground-Based Image of the HR 4796A Circumstellar Disk
• Complex Organic Materials in the Circumstellar Disk of HR 4796A
• Accurate Astrometry and Photometry of Saturated and Coronagraphic Point Spread Functions
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• Discovery of an extended debris disk around the F2V star HD 15745
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• Complex Organic Materials in the HR 4796A Disk?
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• The Integral Field Spectrograph for the Gemini Planet Imager
• The IRCAL Polarimeter: Design, Calibration, and Data Reduction for an Adaptive Optics Imaging Polarimeter
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• Solar System Physics for Exoplanet Research
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• Retrieving Dust Grain Sizes from Photopolarimetry: An Experimental Approach
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• Multiband GPI Imaging of the HR 4796A Debris Disk
• Scattered Light from Dust in the Cavity of the V4046 Sgr Transition Disk
• The Pseudo-zodi Problem for Edge-on Planetary Systems
• The challenge of measuring the phase function of debris disks. Application to HR\,4796
• Irregular dust features around intermediate-mass young stars with GPI: signs of youth or misaligned disks?
• Multiband Polarimetric Imaging of HR 4796A with the Gemini Planet Imager
• New constraints on the dust surrounding HR 4796A
• A Layered Debris Disk around M Star TWA 7 in Scattered Light
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• Automated data processing architecture for the Gemini Planet Imager Exoplanet Survey
• Imaging an 80 AU Radius Dust Ring Around the F5V Star HD 157587
• Quantitative polarimetry of the disk around HD 169142
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• Gemini Planet Imager Observational Calibrations XIV: Polarimetric Contrasts and New Data Reduction Techniques
• Two cold belts in the debris disk around the G-type star NZ Lup
• Kernel Phase and Coronagraphy with Automatic Differentiation
• Infrared Spectroscopy of HR 4796A's Bright Outer Cometary Ring + Tenuous Inner Hot Dust Cloud
• Morphology of the gas-rich debris disk around HD 121617 with SPHERE observations in polarized light
• A millimeter-multiwavelength continuum study of VLA 1623 West
• Sensitivity of the Roman Coronagraph Instrument to Exozodiacal Dust
• Imaging the 44 AU Kuiper Belt-analogue debris ring around HD 141569A with GPI polarimetry
• Karhunen-Loève Data Imputation in High Contrast Imaging
• Adaptive optics in high-contrast imaging
• A Quick Study of Science Return from Direct Imaging Exoplanet Missions: Detection and Characterization of Circumstellar Material with an AFTA or EXO-C/S CGI
• The apparent absence of forward scattering in the HD 53143 debris disk
• Multi-wavelength aperture polarimetry of debris disc host stars
• Debris discs in binaries: morphology and photometric signatures
• SPHERE RefPlanets: Search for epsilon Eridani b and warm dust
• Gaps in Protoplanetary Disks as Signatures of Planets: III. Polarization
• High-contrast integral field spectropolarimetry of planet-forming disks with SCExAO/CHARIS
• Scattering and sublimation: a multi-scale view of $\mu$m-sized dust in the inclined disc of HD 145718
• Performance of the Gemini Planet Imager Non-Redundant Mask and spectroscopy of two close-separation binaries HR 2690 and HD 142527
• Calibration of the instrumental polarization effects of SCExAO-CHARIS' spectropolarimetric mode
• Optical Polarimetry of KIC 8462852 in May-August 2017
• Three new late-type stellar companions to very dusty WISE debris disks identified with VLT/SPHERE imaging
• Full characterization of the instrumental polarization effects of the spectropolarimetric mode of SCExAO-CHARIS