On the Morphology and Chemical Composition of the HR 4796A Debris Disk

Abstract

[abridged] We present resolved images of the HR 4796A debris disk using the Magellan adaptive optics system paired with Clio-2 and VisAO. We detect the disk at 0.77 \microns, 0.91 \microns, 0.99 \microns, 2.15 \microns, 3.1 \microns, 3.3 \microns, and 3.8 \microns. We find that the deprojected center of the ring is offset from the star by 4.76$\pm$1.6 AU and that the deprojected eccentricity is 0.06$\pm$0.02, in general agreement with previous studies. We find that the average width of the ring is 14${}_{-2}^{+3}$, also comparable to previous measurements. Such a narrow ring precludes the existence of shepherding planets more massive than \about 4 \mj, comparable to hot-start planets we could have detected beyond \about 60 AU in projected separation. Combining our new scattered light data with archival HST/STIS and HST/NICMOS data at \about 0.5-2 \microns, along with previously unpublished Spitzer/MIPS thermal emission data and all other literature thermal data, we set out to constrain the chemical composition of the dust grains. After testing 19 individual root compositions and more than 8,400 unique mixtures of these compositions, we find that good fits to the scattered light alone and thermal emission alone are discrepant, suggesting that caution should be exercised if fitting to only one or the other. When we fit to both the scattered light and thermal emission simultaneously, we find mediocre fits (reduced chi-square \about 2). In general, however, we find that silicates and organics are the most favored, and that water ice is usually not favored. These results suggest that the common constituents of both interstellar dust and solar system comets also may reside around HR 4796A, though improved modeling is necessary to place better constraints on the exact chemical composition of the dust.

Accepted to ApJ on October 27, 2014. 21 pages, 12 figures, 4 tables

References in corpus (19)

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Cited by in corpus (22)

• Near-infrared scattered light properties of the HR4796A dust ring: a measured scattering phase function from 13.6deg to 166.6deg
• ALMA observations of the narrow HR 4796A debris ring
• Optical polarized phase function of the HR\,4796A dust ring
• The effect of dust composition and shape on radiation-pressure forces and blowout sizes of particles in debris disks
• Multiband GPI Imaging of the HR 4796A Debris Disk
• The Pseudo-zodi Problem for Edge-on Planetary Systems
• The challenge of measuring the phase function of debris disks. Application to HR\,4796
• Multiband Polarimetric Imaging of HR 4796A with the Gemini Planet Imager
• The Gemini Planet Imager view of the HD 32297 debris disk
• Debris Disk Color with the Hubble Space Telescope
• Characterizing the morphology of the debris disk around the low-mass star GSC~07396-00759
• Infrared Spectroscopy of HR 4796A's Bright Outer Cometary Ring + Tenuous Inner Hot Dust Cloud
• The influence of dust grain porosity on the analysis of debris disc observations
• A Deep Polarimetric Study of the Asymmetrical Debris Disk HD 106906
• MagAO: Status and Science
• A re-investigation of debris disc halos
• Hiding Dust Around $\epsilon$ Eridani
• Millimeter Dust Emission and Planetary Dynamics in the HD 106906 System
• MagAO Imaging of Long-period Objects (MILO). II. A Puzzling White Dwarf around the Sun-like Star HD 11112
• Multi-band reflectance and shadowing of RX J1604.3-2130 protoplanetary disk in scattered light
• A Multiband Study of the HR 4796A Disk in the Optical Using MagAO-X
• The impact of the presence of water ice on the analysis of debris disk observations