Artikel i vetenskaplig tidskrift, 2013

Infrared excesses associated with debris disk host stars detected so far peak at wavelengths around similar to 100 mu m or shorter. However, 6 out of 31 excess sources studied in the Herschel Open Time Key Programme, DUNES, have been seen to show significant-and in some cases extended-excess emission at 160 mu m, which is larger than the 100 mu m excess. This excess emission has been attributed to circumstellar dust and has been suggested to stem from debris disks colder than those known previously. Since the excess emission of the cold disk candidates is extremely weak, challenging even the unrivaled sensitivity of Herschel, it is prudent to carefully consider whether some or even all of them may represent unrelated galactic or extragalactic emission, or even instrumental noise. We re-address these issues using several distinct methods and conclude that it is highly unlikely that none of the candidates represents a true circumstellar disk. For true disks, both the dust temperatures inferred from the spectral energy distributions and the disk radii estimated from the images suggest that the dust is nearly as cold as a blackbody. This requires the grains to be larger than similar to 100 mu m, even if they are rich in ices or are composed of any other material with a low absorption in the visible. The dearth of small grains is puzzling, since collisional models of debris disks predict that grains of all sizes down to several times the radiation pressure blowout limit should be present. We explore several conceivable scenarios: transport-dominated disks, disks of low dynamical excitation, and disks of unstirred primordial macroscopic grains. Our qualitative analysis and collisional simulations rule out the first two of these scenarios, but show the feasibility of the third one. We show that such disks can indeed survive for gigayears, largely preserving the primordial size distribution. They should be composed of macroscopic solids larger than millimeters, but smaller than a few kilometers in size. If larger planetesimals were present, then they would stir the disk, triggering a collisional cascade and thus causing production of small debris, which is not seen. Thus, planetesimal formation, at least in the outer regions of the systems, has stopped before "cometary" or "asteroidal" sizes were reached.

galaxies: statistics

HIP 49908

stars: individual (HIP 29271

HIP 73100)

HIP 171

circumstellar matter

HIP 109378

protoplanetary disks

HIP 92043

planets and satellites: formation


A. Krivov

Friedrich-Schiller-Universität Jena

C. Eiroa

Universidad Autonoma de Madrid (UAM)

T. Lohne

Friedrich-Schiller-Universität Jena

J. P. Marshall

Universidad Autonoma de Madrid (UAM)

B. Montesinos

Centro de Astrobiologia (CAB)

C. del Burgo

Instituto Nacional de Astrofisica Optica y Electronica

O. Absil

Universite de Liège

D. R. Ardila


J. C. Augereau


A. Bayo

European Southern Observatory Santiago

Max Planck-institutet

G. Bryden

Jet Propulsion Laboratory, California Institute of Technology

W. Danchi

NASA Goddard Space Flight Center

S. Ertel


J. Lebreton


René Liseau

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

A. Mora

European Space Astronomy Centre (ESA)

A. J. Mustill

Universidad Autonoma de Madrid (UAM)

H. Mutschke

Friedrich-Schiller-Universität Jena

R. Neuhauser

Friedrich-Schiller-Universität Jena

G.L. Pilbratt


A. Roberge

NASA Goddard Space Flight Center

T. O. B. Schmidt

Friedrich-Schiller-Universität Jena

K. R. Stapelfeldt

NASA Goddard Space Flight Center

P. Thebault

Observatoire de Paris-Meudon

C. Vitense

Friedrich-Schiller-Universität Jena

G. J. White

Rutherford Appleton Laboratory

Open University

S. Wolf

Christian-Albrechts-Universität zu Kiel

Astrophysical Journal

0004-637X (ISSN) 1538-4357 (eISSN)

Vol. 772 1 32


Astronomi, astrofysik och kosmologi