Philippe Thebault

DUst around NEarby Stars. The survey observational results

Context. Debris discs are a consequence of the planet formation process and constitute the fingerprints of planetesimal systems. Their solar system counterparts are the asteroid and Edgeworth-Kuiper belts. Aims. The DUNES survey aims at detecting extra-solar analogues to the Edgeworth-Kuiper belt around solar-type stars, putting in this way the solar system into context. The survey allows us to address some questions related to the prevalence and properties of planetesimal systems. Methods. We used Herschel/PACS to observe a sample of nearby FGK stars. Data at 100 and 160 mu m were obtained, complemented in some cases with observations at 70 mu m, and at 250, 350 and 500 mu m using SPIRE. The observing strategy was to integrate as deep as possible at 100 mu m to detect the stellar photosphere. Results. Debris discs have been detected at a fractional luminosity level down to several times that of the Edgeworth-Kuiper belt. The incidence rate of discs around the DUNES stars is increased from a rate of similar to 12.1% +/- 5% before Herschel to similar to 20.2% +/- 2%. A significant fraction (similar to 52%) of the discs are resolved, which represents an enormous step ahead from the previously known resolved discs. Some stars are associated with faint far-IR excesses attributed to a new class of cold discs. Although it cannot be excluded that these excesses are produced by coincidental alignment of background galaxies, statistical arguments suggest that at least some of them are true debris discs. Some discs display peculiar SEDs with spectral indexes in the 70-160 mu m range steeper than the Rayleigh-Jeans one. An analysis of the debris disc parameters suggests that a decrease might exist of the mean black body radius from the F-type to the K-type stars. In addition, a weak trend is suggested for a correlation of disc sizes and an anticorrelation of disc temperatures with the stellar age.

Collisional processes and size distribution in spatially extended debris discs

Context. New generations of instruments provide, or are about to provide, pan-chromatic images of debris discs and photometric measurements, that require new generations of models, in particular to account for their collisional activity. Aims. We present a new multi-annulus code for the study of collisionally evolving extended debris discs. We first aim to confirm and extend our preliminary result obtained for a single-annulus system, namely that the size distribution in realistic debris discs always departs from the theoretical collisional “equilibrium”

Planetary formation in the γ Cephei system

\mathrm dN \propto R^{-3.5} \mathrm dR

Modelling the huge, Herschel-resolved debris ring around HD 207129

power law, especially in the crucial size range of observable particles (

Planet formation in α Centauri A revisited: not so accretion friendly after all

R\la 1\,

Cold DUst around NEarby Stars (DUNES). First results A resolved exo-Kuiper belt around the solar-like star zeta(2) Ret

cm), where it displays a characteristic wavy pattern. We also study how debris discs density distributions, scattered light luminosity profiles, and Spectral Energy Distributions (SEDs) are affected by the coupled effect of collisions and radial mixing due to radiation pressure affected small grains. Methods. The size distribution evolution is modeled over 10 orders of magnitude, going from μ m-sized grains to 50 km-sized bodies. The model takes into account the crucial influence of radiation pressure-affected small grains. We consider the collisional evolution of a fiducial, idealized

Kuiper belts around nearby stars

a = 120

An interferometric study of the Fomalhaut inner debris disk - III. Detailed models of the exozodiacal disk and its origin

AU radius disc with an initial surface density

Scattering of small bodies by planets: a potential origin for exozodiacal dust?

\Sigma(a) \propto a^{\alpha}

Survival of icy grains in debris discs. The role of photosputtering

. Several key parameters are explored: surface density profile, systems dynamical excitation, total dust mass, collision outcome prescriptions. Results. We show that the systems radial extension plays a crucial role and that the waviness of the size distribution is amplified by inter-annuli interactions: in most regions the collisional and size evolution of the dust is imposed by small particles on eccentric or unbound orbits produced further inside the disc. Moreover, the spatial distribution of all grains