Journal article, 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.

HIP 73100)

stars: individual (HIP 29271

protoplanetary disks

HIP 171

planets and satellites: formation

HIP 49908

circumstellar matter

HIP 92043

galaxies: statistics

HIP 109378


A. Krivov

Friedrich Schiller University Jena

C. Eiroa

Universidad Autonoma de Madrid (UAM)

T. Lohne

Friedrich Schiller University Jena

J. P. Marshall

Universidad Autonoma de Madrid (UAM)

B. Montesinos

Centro de Astrobiologia (CAB)

C. del Burgo

National Institute of Astrophysics, Optics and Electronics

O. Absil

University of Liège

D. R. Ardila

California Institute of Technology (Caltech)

J. C. Augereau

Grenoble Alpes University

A. Bayo

European Southern Observatory Santiago

Max Planck Society

G. Bryden

Jet Propulsion Laboratory, California Institute of Technology

W. Danchi

NASA Goddard Space Flight Center

S. Ertel

Grenoble Alpes University

J. Lebreton

Grenoble Alpes University

René Liseau

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

A. Mora

European Space Astronomy Centre (ESAC)

A. J. Mustill

Universidad Autonoma de Madrid (UAM)

H. Mutschke

Friedrich Schiller University Jena

R. Neuhauser

Friedrich Schiller University Jena

G.L. Pilbratt

European Space Research and Technology Centre (ESA ESTEC)

A. Roberge

NASA Goddard Space Flight Center

T. O. B. Schmidt

Friedrich Schiller University Jena

K. R. Stapelfeldt

NASA Goddard Space Flight Center

P. Thebault

Observatoire de Paris-Meudon

C. Vitense

Friedrich Schiller University Jena

G. J. White

STFC Rutherford Appleton Laboratory

Open University

S. Wolf

University of Kiel

Astrophysical Journal

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

Vol. 772 1 32

Subject Categories

Astronomy, Astrophysics and Cosmology



More information

Latest update

7/9/2021 8