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Context. The nearby and young β Pictoris system hosts a well resolved disk, a directly imaged massive giant planet orbiting at ≃9 au, as well as an inner planet orbiting at ≃2.7 au, which was recently detected through radial velocity (RV). As such, it offers several unique opportunities for detailed studies of planetary system formation and early evolution. Aims. We aim to further constrain the orbital and physical properties of β Pictoris b and c using a combination of high contrast imaging, long base-line interferometry, and RV data. We also predict the closest approaches or the transit times of both planets, and we constrain the presence of additional planets in the system. Methods. We obtained six additional epochs of SPHERE data, six additional epochs of GRAVITY data, and five additional epochs of RV data. We combined these various types of data in a single Markov-chain Monte Carlo analysis to constrain the orbital parameters and masses of the two planets simultaneously. The analysis takes into account the gravitational influence of both planets on the star and hence their relative astrometry. Secondly, we used the RV and high contrast imaging data to derive the probabilities of presence of additional planets throughout the disk, and we tested the impact of absolute astrometry. Results. The orbital properties of both planets are constrained with a semi-major axis of 9.8 ± 0.4 au and 2.7 ± 0.02 au for b and c, respectively, and eccentricities of 0.09 ± 0.1 and 0.27 ± 0.07, assuming the HIPPARCOS distance. We note that despite these low fitting error bars, the eccentricity of β Pictoris c might still be over-estimated. If no prior is provided on the mass of β Pictoris b, we obtain a very low value that is inconsistent with what is derived from brightness-mass models. When we set an evolutionary model motivated prior to the mass of β Pictoris b, we find a solution in the 10–11 MJup range. Conversely, β Pictoris c’s mass is well constrained, at 7.8 ± 0.4 MJup, assuming both planets are on coplanar orbits. These values depend on the assumptions on the distance of the β Pictoris system. The absolute astrometry HIPPARCOS-Gaia data are consistent with the solutions presented here at the 2σ level, but these solutions are fully driven by the relative astrometry plus RV data. Finally, we derive unprecedented limits on the presence of additional planets in the disk. We can now exclude the presence of planets that are more massive than about 2.5 MJup closer than 3 au, and more massive than 3.5 MJup between 3 and 7.5 au. Beyond 7.5 au, we exclude the presence of planets that are more massive than 1–2 MJup. Conclusions. Combining relative astrometry and RVs allows one to precisely constrain the orbital parameters of both planets and to give lower limits to potential additional planets throughout the disk. The mass of β Pictoris c is also well constrained, while additional RV data with appropriate observing strategies are required to properly constrain the mass of β Pictoris b.

The presence of submicron grains has been inferred in several debris discs, despite the fact that these particles should be blown out by stellar radiation pressure on very short timescales. So far, no fully satisfying explanation has been found for this apparent paradox. We investigate the possibility that the observed abundances of submicron grains could be "naturally" produced in bright debris discs, where the high collisional activity produces them at a rate high enough to partially compensate for their rapid removal. We also investigate to what extent this potential presence of small grains can affect our understanding of some debris disc characteristics. We use a code following the collisional evolution of a debris disc down to submicron grains far below the limiting blow-out size $s_{blow}$. We explore different configurations: A and G stars, cold and warm discs, "bright" and "very bright" systems. We find that, in bright discs (fractional luminosity $>10^{-3}$) around A stars, there is always a high-enough amount of submicron grains to leave detectable signatures, both in scattered-light, where the disc's color becomes blue, and in the mid-IR ($10, Comment: Accepted for publication in A&A (abstract shortened to meet astro-ph's criterion)

Planet formation in binary star systems is a complex issue due to the gravitational perturbations of the companion star. One of the crucial steps of the core-accretion model is planetesimal accretion into large protoplanets which finally coalesce into planets. In a planetesimal swarm surrounding the primary star, the average mutual impact velocity determines if larger bodies form or if the population is grinded down to dust, halting the planet formation process. This velocity is strongly influenced by the companion gravitational pull and by gas drag. The combined effect of these two forces may act in favour of or against planet formation, setting a lower or equal probability of the existence of extrasolar planets around single or binary stars. Planetesimal accretion in binaries has been studied so far with two different approaches. N -body codes based on the assumption that the disk is axisymmetric are very cost-effective since they allow the study of the mutual relative velocity with limited CPU usage. A large amount of planetesimal trajectories can be computed making it possible to outline the regions around the star where planet formation is possible. The main limitation of the N -body codes is the axisymmetric assumption. The companion perturbations affect not only the planetesimal orbits, but also the gaseous disk, by forcing spiral density waves. In addition, the overall shape of the disk changes from circular to elliptic. Hybrid codes have been recently developed which solve the equations for the disk with a hydrodynamical grid code and use the computed gas density and velocity vector to calculate an accurate value of the gas drag force on the planetesimals. These codes are more complex and may compute the trajectories of only a limited number of planetesimals.

Observations of the November 1995 Sun crossing of the Saturn's ring-plane made with the 3.6m CFH telescope, using the UHAO adaptive optics system, are presented here. We report the detection of four arcs located in the vicinity of the F ring. They can be seen one day later in HST images. The combination of both data sets gives accurate determinations of their orbits. Semi-major axes range from 140020 km to 140080 km, with a mean of 140060 +- 60 km. This is about 150 km smaller than previous estimates of the F ring radius from Voyager 1 and 2 data, but close to the orbit of another arc observed at the same epoch in HST images., 8 pages, 3 figures, 1 table, To appear in A&A, for comments : charnoz@discovery.saclay.cea.fr

[Abridged] Debris discs around main-sequence stars indicate the presence of larger rocky bodies. The components of the nearby binary aCentauri have higher than solar metallicities, which is thought to promote giant planet formation. We aim to determine the level of emission from debris in the aCen system. Having already detected the temperature minimum, Tmin, of aCenA, we here attempt to do so also for the companion aCenB. Using the aCen stars as templates, we study possible effects Tmin may have on the detectability of unresolved dust discs around other stars. We use Herschel and APEX photometry to determine the stellar spectral energy distributions. In addition, we use APEX for spectral line mapping to study the complex background around aCen seen in the photometric images. Models of stellar atmospheres and discs are used to estimate the amount of debris around these stars. For solar-type stars, a fractional dust luminosity fd 2e-7 could account for SEDs that do not exhibit the Tmin-effect. Slight excesses at the 2.5 sigma level are observed at 24 mu for both stars, which, if interpreted to be due to dust, would correspond to fd (1-3)e-5. Dynamical disc modelling leads to rough mass estimates of the putative Zodi belts around the aCen stars, viz., Comment: 16 pages, 11 figures, accepted by A&A 21 Jan 2014; updated affiliations

In this paper we present the results of several observational campaigns carried out during 1996 at the 1.2 m telescope of the Haute Provence Observatory (France) and at the 1.5m Danish, 0.9m Dutch, 0.6m Bochum and 0.5m telescopes of the European Southern Observatory (ESO, La Silla, Chile), in order to enlarge the available sample of know asteroid rotational periods. A total of 64 single night lightcurves for 15 asteroids were obtained. The rotational periods have been determined for 12 objects, with different quality code: 424 Gratia ( P syn = 19.47 h), 440 Theodora ( P syn = 4.828 h), 446 Aeternitas ( P syn = 15.85 h), 491 Carina ( P syn = 14.87 h), 727 Nipponia ( P syn = 4.6 h), 732 Tjilaki ( P syn = 12.34 h), 783 Nora ( P syn = 34.4 h), 888 Parysatis ( P syn = 5.49 h), 1626 Sadeya ( P syn = 3.438 h), 2209 Tianjin ( P syn = 9.47 h), 2446 Lunacharsky ( P syn = 3.613 h) and 3776 Vartiovuori ( P syn = 7.7 h). For 1246 Chaka, 1507 Vaasa and 1994 Shane the complete rotational phase was not covered and for two of them it was possible to find only an indication of the rotational period.

Astronomy and Astrophysics 561 (2014): A114 reproduced with permission from Astronomy & Astrophysics, Context. The dust observed in debris disks is produced through collisions of larger bodies left over from the planet/planetesimal formation process. Spatially resolving these disks permits to constrain their architecture and thus that of the underlying planetary/planetesimal system. Aims. Our Herschel open time key program DUNES aims at detecting and characterizing debris disks around nearby, sun-like stars. In addition to the statistical analysis of the data, the detailed study of single objects through spatially resolving the disk and detailed modeling of the data is a main goal of the project. Methods. We obtained the first observations spatially resolving the debris disk around the sun-like star HIP 17439 (HD 23484) using the instruments PACS and SPIRE on board the Herschel Space Observatory. Simultaneous multi-wavelength modeling of these data together with ancillary data from the literature is presented. Results. A standard single component disk model fails to reproduce the major axis radial profiles at 70 μm, 100 μm, and 160 μm simultaneously. Moreover, the best-fit parameters derived from such a model suggest a very broad disk extending from few au up to few hundreds of au from the star with a nearly constant surface density which seems physically unlikely. However, the constraints from both the data and our limited theoretical investigation are not strong enough to completely rule out this model. An alternative, more plausible, and better fitting model of the system consists of two rings of dust at approx. 30 au and 90 au, respectively, while the constraints on the parameters of this model are weak due to its complexity and intrinsic degeneracies. Conclusions. The disk is probably composed of at least two components with different spatial locations (but not necessarily detached), while a single, broad disk is possible, but less likely. The two spatially well-separated rings of dust in our best-fit model suggest the presence of at least one high mass planet or several low-mass planets clearing the region between the two rings from planetesimals and dust, S. Ertel and J.-C. Augereau thank the French National Research Agency (ANR, contract ANR-2010 BLAN-0505-01, EXOZODI) and PNP-CNES for financial support. C. Eiroa, J. Maldonado, J. P. Marshall, and B. Montesinos are partially supported by Spanish grant AYA 2011-26202. A. V. Krivov acknowledges support from the DFG, grant Kr 2164/10-1. T. Löhne acknowledges support from the DFG, grant Lo 1715/1-1. R. Liseau acknowledges the continued support by the Swedish National Space Board (SNSB)

We study the dynamics of planetesimals embedded in a circumbinary protoplanetary disk. A hybrid numerical approach is developed where the evolution of the gaseous component of the disk is computed with the hydrodynamical code FARGO while the planetesimal trajectories are computed with an N-body code. The local gas density and velocity derived from the hydrodynamical portion are used to calculate the drag force and the gravitational attraction of the disk on the planetesimals. We explore the effects of spiral density wave patterns and of the disk eccentricity, both excited by the binary tidal perturbations, on the dynamical evolution of planetesimal orbits. A new definition of osculating orbital elements is given to properly account for the gravitational attraction of the disk. The outcomes of the numerical simulations show that the pericenter alignment of the planetesimal orbits is a robust result. It occurs for different values of the binary eccentricity and surface density profiles of the disk. However, the pericenters are less collimated compared to early predictions based on codes adopting a stationary and axisymmetric approximation for the disk. In addition, the eccentricity values are higher and depend on the semimajor axis of the bodies. Both these effects favor higher relative velocities between colliding planetesimals, making accretion less likely than previously thought. Small 100 m size bodies (planetesimal precursors) have a very high inward drift rate that might lead to a high-density belt in the proximity of the inner border of the disk. Fast accretion into larger bodies might occur in this region.

The Epsilon Eridani and 47 UMa extrasolar systems both have moderately massive planets orbiting relatively far away from the central star (at 3.3 and beyond 2.1 AU, respectively). This peculiarity makes them possible candidates for harboring terrestrial planets in their inner regions since the external giant planet might not have inhibited planet growth in the neighborhood of the star. Here we numerically investigate how the accretion of terrestrial planets may have been affected by the presence of the detected giant planets in external orbits. The uncertain timing of the giant planet formation with respect to the planetesimal accumulation process lead us to consider two possible scenarios: 1) the perturbing massive planet was fully formed when the planetesimals in the inner zone were still in their early phases of accumulation, and 2) the giant planet reached its final mass only later on when lunar-sized embryos were already present in the inner disk. In the first case we have used a deterministic numerical algorithm to compute the relative velocity distribution in a swarm of planetesimals affected by the gravitational perturbations of the giant planet and, possibly, by gas drag. The second scenario is explored by using the symplectic algorithm by Chambers (1999) to simulate the late stage of terrestrial planet formation. The Epsilon Eridani system turns out to be a very hostile environment for planetary formation in the terrestrial region when the giant planet formed early. The planet's high eccentricity (0.608) induces very large relative velocities between planetesimals in inner orbits and collisions result mostly in disruption rather than accretion. On the other hand, if large embryos had enough time to form before the completion of the giant planet, they can accrete each other in giant impacts and coalesce into a few terrestrial planets within 0.8 AU from the star. For the 47 UMa system the situation is quite similar. The large mass of the inner giant planet excites large eccentricities among the planetesimals in the terrestrial region preventing accumulation. However, the damping effect on the relative velocities caused by gas drag opens a chance for accretion in a small region around the star inside 0.3 AU. The second and more distant planet recently discovered around 47 Uma does not significantly affect the encounter velocity distribution in the inner regions of the system. As for Epsilon Eridani, orderly growth of lunar-sized embryos takes place within 0.8 AU in presence of a late-formed giant planet. In either case, beyond 0.8 AU planetesimals or planetary embryos are rapidly removed by the massive planet perturbations.