Herschel images of Fomalhaut An extrasolar Kuiper belt at the height of its dynamical activity
Artikel i vetenskaplig tidskrift, 2012

Context. Fomalhaut is a young (2 +/- 1 x 10(8) years), nearby (7.7 pc), 2 M-circle dot star that is suspected to harbor an infant planetary system, interspersed with one or more belts of dusty debris. Aims. We present far-infrared images obtained with the Herschel Space Observatory with an angular resolution between 5.7 '' and 36.7 '' at wavelengths between 70 mu m and 500 mu m. The images show the main debris belt in great detail. Even at high spatial resolution, the belt appears smooth. The region in between the belt and the central star is not devoid of material; thermal emission is observed here as well. Also at the location of the star, excess emission is detected. We aim to construct a consistent image of the Fomalhaut system. Methods. We use a dynamical model together with radiative-transfer tools to derive the parameters of the debris disk. We include detailed models of the interaction of the dust grains with radiation, for both the radiation pressure and the temperature determination. Comparing these models to the spatially resolved temperature information contained in the images allows us to place strong constraints on the presence of grains that will be blown out of the system by radiation pressure. We use this to derive the dynamical parameters of the system. Results. The appearance of the belt points toward a remarkably active system in which dust grains are produced at a very high rate by a collisional cascade in a narrow region filled with dynamically excited planetesimals. Dust particles with sizes below the blow-out size are abundantly present. The equivalent of 2000 one-km-sized comets are destroyed every day, out of a cometary reservoir amounting to 110 Earth masses. From comparison of their scattering and thermal properties, we find evidence that the dust grains are fluffy aggregates, which indicates a cometary origin. The excess emission at the location of the star may be produced by hot dust with a range of temperatures, but may also be due to gaseous free-free emission from a stellar wind.

small particles

planetary system





stars: individual: Fomalhaut


planetary systems

spire instrument


circumstellar matter

debris disk


B. Acke

KU Leuven

M. Min

Anton Pannekoek Institute for Astronomy

Sterrekundig Instituut Utrecht

C. Dominik

Radboud Universiteit

Anton Pannekoek Institute for Astronomy

B. Vandenbussche

KU Leuven

B. Sibthorpe

Royal Observatory

C. Waelkens

KU Leuven

G. Olofsson

Stockholms universitet

P. Degroote

KU Leuven

K. Smolders

KU Leuven

E. Pantin

CNRS Centre National de la Recherche Scientifique

M. J. Barlow

University College London (UCL)

Jadl Blommaert

KU Leuven

A. Brandeker

Stockholms universitet

W. De Meester

KU Leuven

W. R. F. Dent

Atacama Large Millimeter-submillimeter Array (ALMA)

K. M. Exter

KU Leuven

J. Di Francesco

National Research Council Canada

M. Fridlund


W. K. Gear

Cardiff University

A. M. Glauser

Eidgenössische Technische Hochschule Zürich (ETH)

Royal Observatory

J. S. Greaves

University of St Andrews

P. M. Harvey

The University of Texas at Austin

T. Henning

Max Planck-institutet

M. R. Hogerheijde

Universiteit Leiden

W. S. Holland

Royal Observatory

R. Huygen

KU Leuven

R. J. Ivison

University of Edinburgh

Royal Observatory

C. Jean

KU Leuven

René Liseau

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

D. A. Naylor

University of Lethbridge

G.L. Pilbratt


E. T. Polehampton

University of Lethbridge

Rutherford Appleton Laboratory

S. Regibo

KU Leuven

P. Royer

KU Leuven

A. Sicilia-Aguilar

Max Planck-institutet

Universidad Autonoma de Madrid (UAM)

B. M. Swinyard

Rutherford Appleton Laboratory

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 540 Article Number: A125 - A125


Astronomi, astrofysik och kosmologi