J. J. Kavelaars

Resolved debris discs around a stars in the herschel DEBRIS survey

The majority of debris discs discovered so far have only been detected through infrared excess emission above stellar photospheres. While disc properties can be inferred from unresolved photometry alone under various assumptions for the physical properties of dust grains, there is a degeneracy between disc radius and dust temperature that depends on the grain size distribution and optical properties. By resolving the disc we can measure the actual location of the dust. The launch of Herschel, with an angular resolution superior to previous far-infrared telescopes, allows us to spatially resolve more discs and locate the dust directly. Here we present the nine resolved discs around A stars between 20 and 40 pc observed by the DEBRIS survey. We use these data to investigate the disc radii by tting narrow ring models to images at 70, 100 and 160 m and by tting blackbodies to full spectral energy distributions. We do this with the aim of nding an improved way of estimating disc radii for unresolved systems. The ratio between the resolved and blackbody radii varies between 1 and 2.5. This ratio is inversely correlated with luminosity and any remaining discrepancies are most likely explained by dierences to the minimum size of grain in the size distribution or dierences in composition. We nd that three of the systems are well t by a narrow ring, two systems are borderline cases and the other four likely require wider or multiple rings to fully explain the observations, reecting the diversity of planetary systems.

THE SIZE DISTRIBUTION OF KUIPER BELT OBJECTS FOR D ≳ 10 km

We have performed a survey of the Kuiper belt covering ~1/3 deg2 of the sky using Suprime-cam on the Subaru telescope, to a limiting magnitude of m 50(R) ~ 26.8 and have found 36 new Kuiper belt objects (KBOs). We have confirmed that the luminosity function (LF) of the Kuiper belt must break as previously observed. From the LF, we have inferred the underlying size distribution and find that it is consistent with a large object power-law slope q 1 ~ 4.8 that breaks to a slope q 2 ~ 1.9 at object diameter Db ~ 60 km assuming 6% albedos. We have found no conclusive evidence that the size distribution of KBOs with inclinations i 5. We discuss implications of this measurement for early accretion in the outer solar system and Neptune migration scenarios.

The Kuiper belt luminosity function from mR=21 to 26

Abstract We have performed an ecliptic imaging survey of the Kuiper belt with our deepest and widest field achieving a limiting flux of m ( g ′ ) 50 % ∼ 26.4 , with a sky coverage of 3.0 square-degrees. This is the largest coverage of any other Kuiper belt survey to this depth. We detect 72 objects, two of which have been previously observed. We have improved the Bayesian maximum likelihood fitting technique presented in Gladman et al. [Gladman, B., Kavelaars, J.J., Nicholson, P.D., Loredo, T.J., Burns, J.A., 1998. Astron. J. 116, 2042–2054] to account for calibration and sky density variations and have used this to determine the luminosity function of the Kuiper belt. Combining our detections with previous surveys, we find the luminosity function is well represented by a single power-law with slope α = 0.65 ± 0.05 and an on ecliptic sky density of 1 object per square-degree brighter than m R = 23.42 ± 0.13 . Assuming constant albedos, this slope suggests a differential size-distribution slope of 4.25 ± 0.25 , which is steeper than the Dohnanyi slope of 3.5 expected if the belt is in a state of collisional equilibrium. We find no evidence for a roll-over or knee in the luminosity function and reject such models brightward of m ( R ) ∼ 24.6 .

Exploration of the Kuiper Belt by High-Precision Photometric Stellar Occultations: First Results

We report here the first detection of hectometer-size objects by the method of serendipitous stellar occultation. This method consists of recording the diffraction shadow created when an object crosses the observers line of sight and occults the disk of a background star. One of our detections is most consistent with an object between Saturn and Uranus. The two other diffraction patterns detected are caused by Kuiper Belt objects beyond 100 AU from the Sun and hence are the farthest known objects in the solar system. These detections show that the Kuiper Belt is much more extended than previously believed and that the outer part of the disk could be composed of smaller objects than the inner part. This gives critical clues to understanding the problem of the formation of the outer planets of the solar system.

Alignment in star-debris disc systems seen by Herschel

Many nearby main-sequence stars have been searched for debris using the far-infrared Herschel satellite, within the DEBRIS, DUNES and Guaranteed-Time Key Projects. We discuss here 11 stars of spectral types A–M where the stellar inclination is known and can be compared to that of the spatially resolved dust belts. The discs are found to be well aligned with the stellar equators, as in the case of the Sun’s Kuiper belt, and unlike many close-in planets seen in transit surveys. The ensemble of stars here can be fitted with a star–disc tilt of 10 ◦ . These

A POSSIBLE DIVOT IN THE SIZE DISTRIBUTION OF THE KUIPER BELT'S SCATTERING OBJECTS

Via joint analysis of a calibrated telescopic survey, which found scattering Kuiper Belt objects, and models of their expected orbital distribution, we explore the scattering-object (SO) size distribution. Although for D > 100 km the number of objects quickly rise as diameters decrease, we find a relative lack of smaller objects, ruling out a single power law at greater than 99% confidence. After studying traditional knees in the size distribution, we explore other formulations and find that, surprisingly, our analysis is consistent with a very sudden decrease (a divot) in the number distribution as diameters decrease below 100 km, which then rises again as a power law. Motivated by other dynamically hot populations and the Centaurs, we argue for a divot size distribution where the number of smaller objects rises again as expected via collisional equilibrium. Extrapolation yields enough kilometer-scale SOs to supply the nearby Jupiter-family comets. Our interpretation is that this divot feature is a preserved relic of the size distribution made by planetesimal formation, now frozen in to portions of the Kuiper Belt sharing a hot orbital inclination distribution, explaining several puzzles in Kuiper Belt science. Additionally, we show that to match todays SO inclination distribution, the supply source that was scattered outward must have already been vertically heated to the of order 10°.

THE OUTER SOLAR SYSTEM ORIGINS SURVEY. I. DESIGN AND FIRST-QUARTER DISCOVERIES

National Research Council of Canada; National Science and Engineering Research Council of Canada; Academia Sinica Postdoctoral Fellowship

A Uranian Trojan and the Frequency of Temporary Giant-Planet Co-Orbitals

A Uranian Trojan Bodies that share their orbit with that of a planet and that trail or lead the planet by 60° are called Trojans. Based on data from the Canada-France-Hawaii Telescope, Alexandersen et al. (p. 994) have found an object shadowing Uranus that is predicted to remain a Trojan for at least 700,000 years and to stay in co-orbital motion for around one million years before escaping. Observations with the Canada-France-Hawaii Telescope reveal a body that temporarily shares its orbit with that of Uranus. Trojan objects share a planet’s orbit, never straying far from the triangular Lagrangian points, 60° ahead of (L4) or behind (L5) the planet. We report the detection of a Uranian Trojan; in our numerical integrations, 2011 QF99 oscillates around the Uranian L4 Lagrange point for >70,000 years and remains co-orbital for ∼1 million years before becoming a Centaur. We constructed a Centaur model, supplied from the transneptunian region, to estimate temporary co-orbital capture frequency and duration (to a factor of 2 accuracy), finding that at any time 0.4 and 2.8% of the population will be Uranian and Neptunian co-orbitals, respectively. The co-orbital fraction (∼2.4%) among Centaurs in the International Astronomical Union Minor Planet Centre database is thus as expected under transneptunian supply.

A derivation of the luminosity function of the Kuiper belt from a broken power-law size distribution

Abstract We have derived a model of the Kuiper belt luminosity function exhibited by a broken power-law size distribution. This model allows direct comparison of the observed luminosity function to the underlying size distribution. We discuss the importance of the radial distribution model in determining the break diameter. We determine a best-fit break-diameter of the Kuiper belt size-distribution of 30 D b 90 km via a maximum-likelihood fit of our model to the observed luminosity function. We also confirm that the observed luminosity function for m ( R ) ∼ 21 – 28 is consistent with a broken power-law size distribution, and exhibits a break at m ( R ) = 26.0 −1.8 +0.7 .

The Short Rotation Period of Nereid

We determine the period, p = 11.52 ± 0.14 hr, and a light-curve peak-to-peak amplitude, a = 0.029 ± 0.003 mag, of the Neptunian irregular satellite Nereid. If the light-curve variation is due to albedo variations across the surface, rather than solely to the shape of Nereid variations, the rotation period would be a factor of 2 shorter. In either case, such a rotation period and light-curve amplitude, together with Nereids orbital period, p = 360.14 days, imply that Nereid is almost certainly in a regular rotation state, rather than the chaotic rotation state suggested in work of Schaefer & Schaefer and of Dobrovolskis. Assuming that Nereid is perfectly spherical, the albedo variation is 3% across the observed surface. Assuming a uniform geometric albedo, the observed cross-sectional area varies by 3%. We caution that the light curve found in this Letter only sets limits on the combination of albedo and physical irregularity and that we cannot determine the orientation of Nereids spin axis from our data.