Complex Organic Materials in the HR 4796A Disk?

Koehler, Melanie; Mann, Ingrid; Li, Aigen

doi:10.1086/592961

Cited by 19 publications

(22 citation statements)

References 38 publications

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“…Such particles are much smaller than the expected blow-out size in the environment surrounding the central A-type star (e.g., Wyatt et al 1999), and it is thus debatable whether a ring model that is dominated by dust that small is physically plausible. For reference, inferred minimum grain sizes in the HR 4796A ring are typically in the 1-5 μm range (Augereau et al 1999;Li & Lunine 2003;Debes et al 2008;Köhler et al 2008). Furthermore, such small particles result in increasingly more isotropic scattering toward longer wavelengths.…”

Section: Exploratory Scattered Light Models Of the Hr 4796a Ringmentioning

confidence: 99%

Polarimetry With the Gemini Planet Imager: Methods, Performance at First Light, and the Circumstellar Ring Around Hr 4796a

Perrin

Duchêne

Millar-Blanchaer

et al. 2015

ApJ

160

142

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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 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.

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Section: Exploratory Scattered Light Models Of the Hr 4796a Ringmentioning

confidence: 99%

Polarimetry With the Gemini Planet Imager: Methods, Performance at First Light, and the Circumstellar Ring Around Hr 4796a

Perrin

Duchêne

Millar-Blanchaer

et al. 2015

ApJ

160

142

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“…We measure the ring to star contrast by simultaneous unsaturated imaging of both, and thus comparisons between the two color estimates are difficult. Detailed spectral modeling efforts (e.g., Debes et al 2008;Köhler et al 2008) to determine the chemical constituents of the dust would greatly benefit from more accurate color measurements attainable by the next generation of high-contrast instruments.…”

Section: Comparison Of the Reflectivity Of The Dust Ring In Jhk Smentioning

confidence: 99%

The Gemini NICI planet-finding campaign: The offset ring of HR 4796 A

Wahhaj

Liu

Biller

et al. 2014

A&A

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We present J, H, CH 4 short (1.578 μm), CH 4 long (1.652 μm) and K s -band images of the dust ring around the 10 Myr old star HR 4796 A obtained using the Near Infrared Coronagraphic Imager (NICI) on the Gemini-South 8.1 m Telescope. Our images clearly show for the first time the position of the star relative to its circumstellar ring thanks to NICI's translucent focal plane occulting mask. We employ a Bayesian Markov chain Monte Carlo method to constrain the offset vector between the two. The resulting probability distribution shows that the ring center is offset from the star by 16.7 ± 1.3 milliarcseconds along a position angle of 26 ± 3• , along the PA of the ring, 26.47 ± 0.04• . We find that the size of this offset is not large enough to explain the brightness asymmetry of the ring. The ring is measured to have mostly red reflectivity across the JHK s filters, which seems to indicate micron-sized grains. Just like Neptune's 3:2 and 2:1 mean-motion resonances delineate the inner and outer edges of the classical Kuiper belt, we find that the radial extent of the HR 4796 A and the Fomalhaut rings could correspond to the 3:2 and 2:1 mean-motion resonances of hypothetical planets at 54.7 AU and 97.7 AU in the two systems, respectively. A planet orbiting HR 4796 A at 54.7 AU would have to be less massive than 1.6 M Jup so as not to widen the ring too much by stirring.

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“…The ring with a red color in the visible and a gray color in the near-infrared wavelength range led Debes et al (2008) to argue for the presence of complex organic materials like Titan's tholins. In contrast, Köhler et al (2008) modeled the visible to near-infrared spectrum of the ring with porous agglomerates of amorphous silicate, amorphous carbon, and water ice. They considered that spherical constituent grains of a 0 = 0.1 µm coagulated into agglomerates with a porosity p = 0.73.…”

Section: Single Scatteringmentioning

confidence: 99%