Kuiper belts around nearby stars

Abstract

Context. The existence of dusty debris disks around a large fraction of solar type main-sequence stars, inferred from excess far-IR and submillimetre emission compared to that expected from stellar photospheres, suggests that leftover planetesimal belts analogous to the asteroid-and comet reservoirs of the solar system are common. Aims. Sensitive submillimetre observations are essential to detect and characterise cold extended dust originating from collisions of small bodies in disks, belts, or rings at Kuiper-belt distances (30-50 AU or beyond). Measurements of the flux densities at these wavelengths will extend existing IR photometry and permit more detailed modelling of the Rayleigh-Jeans tail of the disks spectral energy distribution (SED), effectively constraining dust properties and disk extensions. By observing stars spanning from a few up to several hundred Myr, the evolution of debris disks during crucial phases of planet formation can be studied. Methods. We observed 22 exo-Kuiper-belt candidates at 870 μm, as part of a large programme with the LABOCA bolometer at the APEX telescope. Dust masses (or upper limits) were calculated from integrated 870 μm fluxes, and fits to the SED of detected sources revealed the fractional dust luminosities fdust, dust temperatures Tdust, and power-law exponents β of the opacity law. Results. A total of 10 detections with at least 3σ significance were made, out of which five (HD 95086, HD 131835, HD 161868, HD 170773, and HD 207129) have previously never been detected at submillimetre wavelengths. Three additional sources are marginally detected with > 2.5σ significance. The best-fit β parameters all lie between 0.1 and 0.8, in agreement with previous results indicating the presence of significantly larger grains than those in the ISM. From our relatively small sample we estimate fdust ∞ t-α, with α ∼ 0.8-2.0, and identify an evolution of the characteristic radial dust distance Rdust that is consistent with the t1/3 increase predicted from models of self-stirred collisions in debris disks. © 2010 ESO.