Debris disks as tracers of small body populations
Final Report Abstract
Debris disks around main-sequence stars are believed to derive from planetesimal populations that have accreted at early epochs and survived possible planet formation processes. While debris disks must contain solids in a broad range of sizes — from big planetesimals down to tiny dust grains — debris disk observations are only sensitive to the dust end of the size distribution. In this project, we have developed a novel approach to access invisible small body populations. It involves physical modeling of the debris disk “from the sources”. We assume that dust is maintained by a belt of parent planetesimals and employ our collisional and radiative transfer codes to consistently model the size and radial distribution of the disk material and then thermal emission of dust. A comparison of the modeled emission with the one actually observed allow us to constrain various parameters, including the stellar properties, the exact location, extension, and dynamical excitation of the planetesimal belt, chemical composition of solids, and the collisional prescription. We have used our approach to interpret (i) statistics of a large number of observed (generally, unresolved) debris disks, (ii) spectral energy distribution of individual unresolved systems, and (iii) all avaliable observational data of resolved disks. Our main results are as follows: (i) We have established several general scaling rules for the disk evolution and showed that the observed decay rate of the dust luminosity is primarily determined by the “primordial” size distribution of largest planetesimals, which has been set up at their accretion phase, and by the size distribution of somewhat smaller, yet gravity-dominated, planetesimals that have already undergone suf?cient collisional evolution. The observed statistics of the fractional luminosity versus age is consistent with our models. (ii) By analysis of spectral energy distribution of five particular disks around sun-like stars, we have shown that these are likely maintained by “large Kuiper belts” of 0.2–50 earth masses (in the bodies up to 100 km in size) with radii of 100–200 AU. However, this comes with a warning that these results depend sensitively on the assumptions about chemical composition of dust. (iii) Our results for the archetypical debris disk around Vega suggest that, contrary to previous claims, the Vega disk observations are not in contradiction with a steady-state collisional dust production. Furthermore, we put important constraints on the parameters. We show, in particular, that including cratering collisions into the model is mandatory. We also demonstrate that using an intermediate luminosity of the star between the pole and the equator, as derived from its fast rotation, is required to reproduce the debris disk observations. Finally, we favor a scenario in which the collisional cascade ignited early in the history of the Vega system. Our results have been published in several papers in international peer-reviewed journals and presented at a number of conferences. Some aspects of our research have also been communicated to general public through press releases of the University Jena, publications in newspapers (Frankrurter Allgemeine Zeitung, Thüringer Landeszeitung), and radio broadcasting (Deutschlandfunk, Südwestrundfunk).
Publications
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(2008). Collisional and Thermal Emission Models of Debris Disks: Towards Planetesimal Population Properties. Astrophysical Journal 687, 608–622
A.V. Krivov, S. Müller, T. Löhne, and H. Mutschke
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(2008). Long-Term Collisional Evolution of Debris Disks. Astrophysical Journal 673, 1123–1137
T. Löhne, A.V. Krivov, and J. Rodmann
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(2009). A possible architecture of the planetary system HR 8799. Astronomy and Astrophysics 503, 247–258
M. Reidemeister, A.V. Krivov, T. O. B. Schmidt, S. Fiedler, S. Müller, T. Löhne, and R. Neuhäuser
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(2009). What Children Tell Us about Their Parents: From Visible Dust to Invisible Planetesimals in Debris Disks. Bull. Amer. Astron. Soc., 40, 392
S. Müller, A.V. Krivov, T. Löhne, and H. Mutschke
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(2009). The Debris Disk of Vega: A Steady-State Collisional Cascade? Astrophysical Journal
S. Müller, T. Löhne, and A.V. Krivov
