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Hubble to revisit exoplanet puzzle

Pinning down the elusive nature of Fomalhaut b, a faint speck of light discerned within the glare of a nearby star, has proved to be far from childs play. At stake are bragging rights to the first optical image of an exoplanet, and one that is close enough to be studied in detail. But since Fomalhaut b was first reported in 2008, its identity has been the subject of intense debate. The next round of Hubble Space Telescope observations, scheduled to begin on 27 May, could help to resolve the controversy.
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Title: Herschel images of Fomalhaut. An extrasolar Kuiper Belt at the height of its dynamical activity
Authors: B. Acke, M. Min, C. Dominik, B. Vandenbussche, B. Sibthorpe, C. Waelkens, G. Olofsson, P. Degroote, K. Smolders, E. Pantin, M. J. Barlow, J. A. D. L. Blommaert, A. Brandeker, W. De Meester, W. R. F. Dent, K. Exter, J. Di Francesco, M. Fridlund, W. K. Gear, A. M. Glauser, J. S. Greaves, P. M. Harvey, Th. Henning, M. R. Hogerheijde, W. S. Holland, R. Huygen, R. J. Ivison, C. Jean, R. Liseau, D. A. Naylor, G. L. Pilbratt, E. T. Polehampton, S. Regibo, P. Royer, A. Sicilia-Aguilar, B.M. Swinyard

Fomalhaut is a young, nearby star that is suspected to harbour an infant planetary system, interspersed with one or more belts of dusty debris. We present far-infrared images obtained with the Herschel Space Observatory with an angular resolution between 5.7 and 36.7 arcsec at wavelengths between 70 and 500 micrometer. 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 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.
The appearance of the belt points towards 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.

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ALMA Reveals Workings of Nearby Planetary System

A new observatory still under construction has given astronomers a major breakthrough in understanding a nearby planetary system and provided valuable clues about how such systems form and evolve. Astronomers using the Atacama Large Millimetre/submillimetre Array (ALMA) have discovered that planets orbiting the star Fomalhaut must be much smaller than originally thought. This is the first published science result from ALMA in its first period of open observations for astronomers worldwide.
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Herschel spots comet massacre around nearby star

ESA's Herschel Space Observatory has studied the dusty belt around the nearby star Fomalhaut. The dust appears to be coming from collisions that destroy up to thousands of icy comets every day.
Fomalhaut is a young star, just a few hundred million years old, and twice as massive as the Sun. Its dust belt was discovered in the 1980s by the IRAS satellite, but Herschel's new images of the belt show it in much more detail at far-infrared wavelengths than ever before.

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Crushing 2000 comets per day in another planetary system

New images from ESA's Herschel Space Observatory reveal the glow from dust in the debris disk - a structure resembling the Kuiper Belt in the primordial Solar System - around the young star Fomalhaut. Detailed studies suggest that the dust in this debris disk consists of 'fluffy' aggregates of grains, which are produced by the frequent collisions taking place between comets within the disk.
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Fomalhaut b "first" planet picture in doubt

The Hubble space telescope's first photo of a planet, Fomalhaut b, orbiting a nearby star, may actually be "scattered dust" and not a planet, reports an astronomy team.
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Title: Infrared Non-detection of Fomalhaut b -- Implications for the Planet Interpretation
Authors: Markus Janson, Joe Carson, David Lafreniere, David Spiegel, John Bent, Palmer Wong

The nearby A4-type star Fomalhaut hosts a debris belt in the form of an eccentric ring, which is thought to be caused by dynamical influence from a giant planet companion. In 2008, a detection of a point-source inside the inner edge of the ring was reported and was interpreted as a direct image of the planet, named Fomalhaut b. The detection was made at ~600--800 nm, but no corresponding signatures were found in the near-infrared range, where the bulk emission of such a planet should be expected. Here we present deep observations of Fomalhaut with Spitzer/IRAC at 4.5 um, using a novel PSF subtraction technique based on ADI and LOCI, in order to substantially improve the Spitzer contrast at small separations. The results provide more than an order of magnitude improvement in the upper flux limit of Fomalhaut b and exclude the possibility that any flux from a giant planet surface contributes to the observed flux at visible wavelengths. This renders any direct connection between the observed light source and the dynamically inferred giant planet highly unlikely. We discuss several possible interpretations of the total body of observations of the Fomalhaut system, and find that the interpretation that best matches the available data for the observed source is scattered light from transient or semi-transient dust cloud.

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Title: Fomalhaut debris disk emission at 7 millimetres: constraints on the collisional models of planetesimals
Authors: L. Ricci, L. Testi, S. T. Maddison, D. J. Wilner

We present new spatially resolved observations of the dust thermal emission at 7 mm from the Fomalhaut debris disk obtained with the Australia Telescope Compact Array. These observations provide the longest wavelength detection of the Fomalhaut debris disk to date. We combined the new data to literature sub-mm data to investigate the spectral index of the dust thermal emission in the sub-millimetre and constrained the q-slope of the power-law grain size distribution. We derived a value for q = 3.48 0.14 for grains with sizes around 1 mm. This is consistent with the classical prediction for a collisional cascade at the steady-state. The same value cannot be explained by more recent collisional models of planetesimals in which either the velocity distribution of the large bodies or their tensile strength is a strong function of the body size.

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Exoplanet's misstep raises doubts

As astronomers continue to rack up exoplanet discoveries by the dozen, the precise status of just one may not seem like much to fret over. But Fomalhaut b is different.
Unveiled in 2008, the tiny dot spotted circling Fomalhaut, a star just 25 light years from our own solar system, was billed as the first exoplanet to be directly imaged at optical wavelengths. Now Fomalhaut b's identity is being questioned after new data, presented last week at an exoplanet conference in Grand Teton National Park, Wyoming, shows it has moved in an unexpected way.

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Title: Optical Images of an Exosolar Planet 25 Light Years from Earth
Authors: Paul Kalas (1), James R. Graham (1), Eugene Chiang (1,2), Michael P. Fitzgerald (3), Mark Clampin (4), Edwin S. Kite (2), Karl Stapelfeldt (5), Christian Marois (6), John Krist (5) ((1) Astronomy Department, University of California, Berkeley, CA, USA (2) Department of Earth & Planetary Science, University of California, Berkeley, CA, USA (3) Lawrence Livermore National Laboratory, Livermore, CA, USA (4) Goddard Space Flight Centre, Greenbelt, MD, USA (5) Jet Propulsion Laboratory, Pasadena, CA, USA (6) Herzberg Institute for Astrophysics, Victoria, BC, Canada)
(13 Nov 2008, Version, v2)

Fomalhaut is a bright star 7.7 parsecs (25 light years) from Earth that harbours a belt of cold dust with a structure consistent with gravitational sculpting by an orbiting planet. Here, we present optical observations of an exoplanet candidate, Fomalhaut b. In the plane of the belt, Fomalhaut b lies approximately 119 astronomical units (AU) from the star and 18 AU from the belt, matching predictions. We detect counterclockwise orbital motion using Hubble Space Telescope observations separated by 1.73 years. Dynamical models of the interaction between the planet and the belt indicate that the planet's mass is at most three times that of Jupiter for the belt to avoid gravitational disruption. The flux detected at 800 nm is also consistent with that of a planet with mass no greater than a few times that of Jupiter. The brightness at 600 nm and the lack of detection at longer wavelengths suggest that the detected flux may include starlight reflected off a circumplanetary disk, with dimension comparable to the orbits of the Galilean satellites. We also observed variability of unknown origin at 600 nm.

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Fomalhaut b is an extrasolar planet approximately 25 light-years away in the constellation of Piscis Austrinus.
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