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An Interferometric Study of the Fomalhaut Inner Debris Disk. II. Keck Nuller Mid-infrared Observations

Mennesson, B. and Absil, O. and Lebreton, J. and Augereau, J.-C. and Serabyn, E. and Colavita, M. M. and Millan-Gabet, R. and Liu, W. and Hinz, P. and Thébault, P. (2013) An Interferometric Study of the Fomalhaut Inner Debris Disk. II. Keck Nuller Mid-infrared Observations. Astrophysical Journal, 763 (2). Art. No. 119. ISSN 0004-637X.

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We report on high-contrast mid-infrared observations of Fomalhaut obtained with the Keck Interferometer Nuller (KIN) showing a small resolved excess over the level expected from the stellar photosphere. The measured null excess has a mean value of 0.35% ± 0.10% between 8 and 11 μm and increases from 8 to 13 μm. Given the small field of view of the instrument, the source of this marginal excess must be contained within 2 AU of Fomalhaut. This result is reminiscent of previous VLTI K-band (≃2μm) observations, which implied the presence of a ~0.88% excess, and argued that thermal emission from hot dusty grains located within 6 AU from Fomalhaut was the most plausible explanation. Using a parametric two-dimensional radiative transfer code and a Bayesian analysis, we examine different dust disk structures to reproduce both the near- and mid-infrared data simultaneously. While not a definitive explanation of the hot excess of Fomalhaut, our model suggests that the most likely inner few AU disk geometry consists of a two-component structure, with two different and spatially distinct grain populations. The 2-11 μm data are consistent with an inner hot ring of very small (≃10-300 nm) carbon-rich grains concentrating around 0.1 AU. The second dust population—inferred from the KIN data at longer mid-infrared wavelengths—consists of larger grains (size of a few microns to a few tens of microns) located further out in a colder region where regular astronomical silicates could survive, with an inner edge around 0.4 AU-1 AU. From a dynamical point of view, the presence of the inner concentration of submicron-sized grains is surprising, as such grains should be expelled from the inner planetary system by radiation pressure within only a few years. This could either point to some inordinate replenishment rates (e.g., many grazing comets coming from an outer reservoir) or to the existence of some braking mechanism preventing the grains from moving out.

Item Type:Article
Related URLs:
URLURL TypeDescription
Mennesson, B.0000-0003-4205-4800
Absil, O.0000-0002-4006-6237
Lebreton, J.0000-0003-1476-5963
Millan-Gabet, R.0000-0003-0447-5866
Hinz, P.0000-0002-1954-4564
Additional Information:© 2013 American Astronomical Society. Received 2012 July 23; accepted 2012 November 27; published 2013 January 16. The Keck Interferometer was funded by the National Aeronautics and Space Administration (NASA). Part of this work was performed at the Jet Propulsion Laboratory, California Institute of Technology, and at the NASA Exoplanet Science Center (NExSci), under contract with NASA. The Keck Observatory was made possible through the generous financial support of the W. M. Keck Foundation. O. Absil, J.-C. Augereau, J. Lebreton, and P. Thébault thank the French National Research Agency (ANR, contract ANR-2010 BLAN-0505-01, EXOZODI) for financial support.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
W. M. Keck FoundationUNSPECIFIED
Agence Nationale pour la Recherche (ANR)ANR-2010 BLAN-0505-01
Subject Keywords:circumstellar matter; infrared: stars; instrumentation: interferometers; stars: individual (Fomalhaut)
Issue or Number:2
Record Number:CaltechAUTHORS:20130222-134812615
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Official Citation:An Interferometric Study of the Fomalhaut Inner Debris Disk. II. Keck Nuller Mid-infrared Observations B. Mennesson, O. Absil, J. Lebreton, J.-C. Augereau, E. Serabyn, M. M. Colavita, R. Millan-Gabet, W. Liu, P. Hinz, and P. Thébault doi:10.1088/0004-637X/763/2/119
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:37085
Deposited By: Ruth Sustaita
Deposited On:22 Feb 2013 22:08
Last Modified:07 Apr 2020 19:18

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