Search

Discs in binaries have a complex behavior because of the perturbations of the companion star. Planet formation in binary-star systems both depend on the companion star parameters and on the properties of the circumstellar disc. An eccentric disc may increase the impact velocity of planetesimals and therefore jeopardize the accumulation process. We model the evolution of discs in close binaries including the effects of self-gravity and adopting different prescriptions to model the disc's radiative properties. We focus on the dynamical properties and evolutionary tracks of the discs. We use the hydrodynamical code FARGO and we include in the energy equation heating and cooling effects. Radiative discs have a lower disc eccentricity compared to locally isothermal discs with same temperature profile. As a consequence, we do not observe the formation of an internal elliptical low density region as in locally isothermal disc models. However, the disc eccentricity depends on the disc mass through the opacities. Akin to locally isothermal disc models, self-gravity forces the disc's longitude of pericenter to librate about a fixed orientation with respect to the binary apsidal line ($\pi$). The disc's radiative properties play an important role in the evolution of discs in binaries. A radiative disc has an overall shape and internal structure that are significantly different compared to a locally isothermal disc with same temperature profile. This is an important finding both for describing the evolutionary track of the disc during its progressive mass loss, and for planet formation since the internal structure of the disc is relevant for planetesimals growth in binary systems. The non-symmetrical distribution of mass in these discs causes large eccentricities for planetesimals that may affect their growth., Comment: accepted for publication in A&A (abstract truncated to comply with astro-ph rules)

Hydrodynamical simulations of two giant planets embedded in a gaseous disk have shown that in case of a smooth convergent migration they end up trapped into a mean motion resonance. These findings have led to the conviction that the onset of dynamical instability causing close encounters between the planets can occur only after the dissipation of the gas when the eccentricity damping is over. We show that a system of three giant planets may undergo planet-planet scattering when the gaseous disk, with density values comparable to that of the Minimum Mass Solar Nebula, is still interacting with the planets. The hydrodynamical code FARGO--2D--1D is used to model the evolution ofthe disk and planets, modified to properly handle close encounters between the massive bodies. Our simulations predict a variety of different outcomes of the scattering phase which includes orbital exchange, planet merging and scattering of a planet in a hyperbolic orbit. This implies thatthe final fate of a multiplanet system under the action of the disk torques is not necessarily a packed resonant configuration., Comment: Astronomy and Astrophysics Letters, in press

We study the evolution of circumstellar massive disks around the primary star of a binary system focusing on the computation of disk eccentricity. In particular, we concentrate on its dependence on the binary eccentricity. Self-gravity is included in our numerical simulations. Our standard model assumes a semimajor axis for the binary of 30 AU, the most probable value according to the present binary statistics., Comment: Accepted for publication on A&A

We explore planet formation in binary systems around the central star where the protoplanetary disk plane is highly inclined with respect to the companion star orbit. This might be the most frequent scenario for binary separations larger than 40 AU, according to Hale (1994). We focus on planetesimal accretion and compute average impact velocities in the habitable region and up to 6 AU from the primary., Comment: Accepted for publication on A&A

We study the dynamics of Jupiter Trojans in the early phase of the Solar system while the outer planets migrated due to their interaction with the planetesimal disk., Comment: 10 pages, 17 figures

We investigate classical planetesimal accretion in a binary star system of separation ab<50AU by numerical simulations, with particular focus on the region at a distance of 1 AU from the primary. The planetesimals orbit the primary, are perturbed by the companion and are in addition subjected to a gas drag force. We concentrate on the problem of relative velocities dv among planetesimals of different sizes. For various stellar mass ratios and binary orbital parameters we determine regions where dv exceed planetesimal escape velocities v_esc (thus preventing runaway accretion) or even the threshold velocity v_ero for which erosion dominates accretion. Gaseous friction has two crucial effects on the velocity distribution: it damps secular perturbations by forcing periastron alignment of orbits, but at the same time the size--dependence of this orbital alignment induces a significant dv increase between bodies of different sizes. This differential phasing effect proves very efficient and almost always increases dv to values preventing runaway accretion, except in a narrow domain of almost circular companion orbits. The erosion threshold dv>v_ero is reached in a wide (ab,eb) space for small (<10km) planetesimals, but in a much more limited region for bigger ~50km objects. In the intermediate v_esc

We present the data acquisition strategy and characterization procedures for the Canada-France Ecliptic Plane Survey (CFEPS), a sub-component of the Canada-France-Hawaii Telescope Legacy Survey. The survey began in early 2003 and as of summer 2005 has covered 430 square degrees of sky within a few degrees of the ecliptic. Moving objects beyond the orbit of Uranus are detected to a magnitude limit of $m_R$=23 -- 24 (depending on the image quality). To track as large a sample as possible and avoid introducing followup bias, we have developed a multi-epoch observing strategy that is spread over several years. We present the evolution of the uncertainties in ephemeris position and orbital elements as the objects progress through the epochs. We then present a small 10-object sample that was tracked in this manner as part of a preliminary survey starting a year before the main CFEPS project. We describe the CFEPS survey simulator, to be released in 2006, which allows theoretical models of the Kuiper Belt to be compared with the survey discoveries since CFEPS has a well-documented pointing history with characterized detection efficiencies as a function of magnitude and rate of motion on the sky. Using the pre-survey objects we illustrate the usage of the simulator in modeling the classical Kuiper Belt., Comment: to be submitted to Icarus

At present the possible existence of planets around the stars of a close binary system is still matter of debate. Can planetary bodies form in spite of the strong gravitational perturbations of the companion star? We study in this paper via numerical simulation the last stage of planetary formation, from embryos to terrestrial planets in the Alpha Cen system, the prototype of close binary systems. We find that Earth class planets can grow around Alpha Cen A on a time-scale of 50 Myr. In some of our numerical models the planets form directly in the habitable zone of the star in low eccentric orbits. In one simulation two of the final planets are in a 2:1 mean motion resonance that, however, becomes unstable after 200 Myr. During the formation process some planetary embryos fall into the stars possibly altering their metallicity., Comment: accepted for pubblication in A&A, 13 pages, 9 figures

We have performed a series of high resolution N-body experiments on a Connection Machine CM-5 in order to study the stability of collisionless self-gravitating spherical systems. We interpret our results in the framework of symplectic mechanics, which provides the definition of a new class of particular perturbations: The preserving perturbations, which are a generalization of the radial ones. Using models defined by the Ossipkov-Merritt algorithm, we show that the stability of a spherical anisotropic system is directly related to the preserving or non-preserving nature of the perturbations acting on the system. We then generalize our results to all spherical systems. Since the ``isotropic component'' of the linear variation of the distribution function cannot be used to predict the stability or instability of a spherical system, we propose a more useful stability parameter which is derived from the ``anisotropic'' component of the linear variation., Comment: uuencoded gzip compressed postscript file containing 14 pages, accepted for publication in MNRAS

We propose a morphological multi-scale analysis of large-scale structures obtained by computer simulations and by observations. Structures are obtained at different scales by applying a wavelet transform on the observed and simulated data. Application of a segmentation algorithm allows a quantitative morphological description of the structures at each scale. The morphological parameter which we propose represents the deviation of a structure from sphericity. The dependence on scale of this simple parameter is shown to characterize in simulations the underlying cosmological model. We compare the HDM, CDM and mixed models with the CfA catalogue. This comparison favours a mixed model containing $65\%$ of CDM, $30\%$ of HDM, and $5\%$ baryonic matter., Comment: uuencoded compressed postscript file, accepted for publication in Astronomy and Astrophysics

We have performed a series of N-body experiments on Connection Machine-5 in order to simulate the formation of galaxy clusters gravitationally dominated by a massive dark background. In accordance with previous authors we find an extremely inhomogeneous evolution where subcondensations are continually formed and merged. The final distribution of galaxies is more centrally condensed than that of dark matter particles. We have analyzed the origin of this galaxy-dark matter segregation and also the origin of subclustering leading to this effect. We have then analysed, analytically and numerically, the dependence of final segregation on the physical parameters characterizing the model of protocluster. We also find that such a segregation persists even when inelastic encounters of dark halos around galaxies are taken into account. We conclude that this effect cannot be in general avoided in any hierarchical clustering scenario., Comment: 26 pages plus 13 figures (4 of which, not included, available upon request to serna@frmeu51.bitnet), postscript, Preprint OP-93030