Herschel images of Fomalhaut An extrasolar Kuiper belt at the height of its dynamical activity
Journal article, 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.
evolution
spire instrument
planetary systems
small particles
circumstellar matter
debris disk
stars
light
radiation
planetary system
dust
grains
stars: individual: Fomalhaut
Author
B. Acke
KU Leuven
M. Min
Anton Pannekoek Institute for Astronomy
Utrecht University
C. Dominik
Radboud University
Anton Pannekoek Institute for Astronomy
B. Vandenbussche
KU Leuven
B. Sibthorpe
Royal Observatory
C. Waelkens
KU Leuven
G. Olofsson
Stockholm University
P. Degroote
KU Leuven
K. Smolders
KU Leuven
E. Pantin
Centre national de la recherche scientifique (CNRS)
M. J. Barlow
University College London (UCL)
Jadl Blommaert
KU Leuven
A. Brandeker
Stockholm University
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
European Space Agency (ESA)
W. K. Gear
Cardiff University
A. M. Glauser
Royal Observatory
Swiss Federal Institute of Technology in Zürich (ETH)
J. S. Greaves
University of St Andrews
P. M. Harvey
University of Texas
T. Henning
Max Planck Society
M. R. Hogerheijde
Leiden University
W. S. Holland
Royal Observatory
R. Huygen
KU Leuven
R. J. Ivison
Royal Observatory
University of Edinburgh
C. Jean
KU Leuven
René Liseau
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
D. A. Naylor
University of Lethbridge
G.L. Pilbratt
European Space Agency (ESA)
E. T. Polehampton
University of Lethbridge
STFC Rutherford Appleton Laboratory
S. Regibo
KU Leuven
P. Royer
KU Leuven
A. Sicilia-Aguilar
Max Planck Society
Universidad Autonoma de Madrid (UAM)
B. M. Swinyard
STFC Rutherford Appleton Laboratory
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 540 Article Number: A125 - A125Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
DOI
10.1051/0004-6361/201118581