Mean-Motion Resonances as a Source for Infalling Comets toward β Pictoris

Repeated time-variable redshifted absorption features in the spectrum of β Pictoris (β Pic) have been attributed to comet-like bodies falling toward the star, when evaporating in its immediate vicinity. This model explains now a large number of observational characteristics, but the exact mechanism that could generate these numerous star-grazers is still controversial, even if planetary perturbations are thought to be the basic process. The different models proposed up to now are here reviewed, and we discuss in particular a recent one, involving the effect of secular resonances in the β Pic system. We stress that it seems highly improbable that such a mechanism could apply to the β Pic case, because the extremely strong power of secular resonances is connected to the very specific structure of the Solar System. Therefore, the secular resonance mechanism is highly non-generic. Conversely, we propose a model involving the eccentricity-pumping effect of mean-motion resonances with a massive planet on a moderately eccentric orbit. We show in particular that the 4:1 mean-motion resonance is a very active source of star-grazers as soon as the eccentricity of the perturbing planet is ?0.05, while the 3:1 mean-motion resonance is less efficient. We stress that this mechanism is very generic. These theoretical predictions are confirmed by numerical integrations using the Extended Schubart Integrator. The time-scale of the process is discussed, and we show that if the eccentricity of the perturbing planet fluctuates, due to secular perturbations, this time-scale is compatible with the age of β Pic's system.     

Formation of the binary near‐Earth object 1996 FG3: Can binary NEOs be the source of short‐CRE meteorites?

Abstract— 1996 FG₃ is a binary near‐Earth object (NEO) that was likely formed during a tidal disruption event. Our results indicate that the formation of this binary object was unlikely to have occurred when the progenitor had a encounter velocity with the Earth significantly smaller than its current value (10.7 km/s); The formation of the binary object on an orbit similar to the present one is possible, and the survival of the satellite constrains this to have happened less than 1.6 Ma ago. However, the binary object could also have been formed when the progenitor's encounter velocity with Earth was >12 km/s, and in this case we cannot constrain its formation age. Our results indicate that tidal disruptions occurring among NEOs with low velocity encounters with Earth are unlikely to produce long‐lasting NEO binaries. Thus, tidal disruption may not be able to completely re‐supply the observed population. This would imply that a significant fraction of the observed NEO binaries evolved out of the main asteroid belt. Overall, our results suggest to us that the CM2 meteorites having cosmic ray exposure (CRE) ages of ?200,000 yr were likely liberated by the tidal disruption of a primitive NEO with a relative velocity with the Earth significantly smaller than that of 1996 FG₃. We propose a list of such objects, although as far as we know, none of the candidates is a binary for the reasons described above.     

The researches at torino on wide double stars

Summary The present poster shows the main researches conduced at the Astronomical Observatory of Torino during this last decade in the field of the wide double stars. From the observational point of view, two different photographic techniques carried out with our 105 cm astrometric reflector over a selected sample of wide binaries are explained. With reference to the Hipparcos mission, we show two aspects of our collaboration with the INCA and FAST Consortiums. From the statistical point of view, a study concerning the systematic and accidental errors detected in visual double star observations is explained. We conclude the poster with the future foreseen researches concerning new observational techniques and new theoretical statistical studies on these wide objects.     

On the relationship between Lyapunov times and macroscopic instability times

On the basis of the general theory of Hamiltonian systems, we consider the relationship between Lyapunov times and macroscopic diffusion times. We find out that there are two regimes: the Nekhoroshev regime and the resonant overlapping regime. In the first case the diffusion time is exponentially long with respect to Lyapunov times. In the second case, the relationship is polynomial although we do not find any theoretical reason for the existence of a universal power law. We show numerical evidences which confirm our theoretical considerations.     

Magmatism and fenitization in the Cretaceous potassium-alkaline-carbonatitic complex of Ipanema S?o Paulo State, Brazil

The Ipanema alkaline-carbonatitic complex is part of the Meso-Cenozoic alkaline magmatism located within the southeastern part of the Brazilian Platform. Drill-core and field sampling have indicated the occurrence of glimmerites, with subordinate shonkinites (mela-syenites), clinopyroxene-bearing glimmerites, diorites and syenites. The glimmerites are cross-cut by lamprophyric dykes and calciocarbonatites. Fenitization has deeply affected the country rocks, originating dioritic and syenitic rocks. The Ipanema rocks show a distinct potassic affinity. The initial Sr-Nd- isotopic composition of the Ipanema rocks (⁸⁷Sr/⁸⁶Sr?=?0.70661–0.70754 and ¹⁴³Nd/¹⁴⁴Nd?=?0.51169–0.51181) is similar to that of tholeiitic and potassium-rich-alkaline rocks of the Eastern Paraguay. Stable isotope data for the Ipanema calciocarbonatite suggest interaction with fluids at temperatures typical of hydrothermal stages, as hypothesized for other carbonatite complexes from southeastern Brazil. The chemical differences between the lamprophyre, glimmerites, carbonatites, apatitites and magnetitites, and the absence of marked REE enrichment in the evolved lithologies, all indicate that fractional crystallization and accumulus of liquidus phases in a magma reservoir, likely coupled with liquid immiscibility processes, may have played an important role in the genesis of the Ipanema rocks.     

旋转扰动流体中壁面湍流不稳定及其拟序结构研究Ⅰ:实验

重点介绍和讨论了中性条件下旋转扰动流体中边界层强迫不稳定及其相关的一些问题,阐述了旋转体系中切变驱动边界层不稳定的动力学特征.这些不稳定状态的研究在大气物理学、流体动力学、海洋学等多个领域中引起科学家极大的兴趣,近年来在实验和理论研究中都得到了不断的发展.意大利都灵大学基础物理系地球科学实验组通过水槽旋转实验方法,不断改变水槽启动或结束时的旋转运动速度,以及底部壁面粗糙度等要素,所得到的实验结果与SDBL理论非常一致.     

Ages (U–Pb SHRIMP and LA ICPMS) and stratigraphic evolution of the Neoproterozoic volcano-sedimentary successions from the extensional Camaquã Basin,Southern Brazil

During the Ediacaran, southern Brazil was the site of multiple episodes of volcanism and sedimentation, which are best preserved in the 3000 km² Camaquã Basin. The interlayered sedimentary and volcanic rocks record tectonic events and paleoenvironmental changes in a more than 10 km-thick succession. In this contribution, we report new U–Pb and Sm–Nd geochronological constraints for the 605 to 580 Ma Bom Jardim Group, the 570 Ma Acampamento Velho Formation, and a newly-recognized 544 Ma volcanism. Depositional patterns of these units reveal the transition from a restricted, fault-bounded basin into a wide, shallow basin. The expansion of the basin and diminished subsidence rates are demonstrated by increasing areal distribution and compressed isopachs and increasing onlap of sediments onto the basement to the west. The Sm–Nd isotopic composition of the volcanic rocks indicates mixed sources, including crustal rocks from the adjacent basement. Both Neoproterozoic and Paleoproterozoic sources are indicated for the western part of the basin, whereas only the older Paleoproterozoic signature can be discerned in the eastern part of the basin.     

Dynamical capture in the Pluto–Charon system

This paper explores the possibility that the progenitors of the small satellites of Pluto got captured in the Pluto?CCharon system from the massive heliocentric planetesimal disk in which Pluto was originally embedded into. We find that, if the dynamical excitation of the disk is small, temporary capture in the Pluto?CCharon system can occur with non- negligible probability, due to the dynamical perturbations exerted by the binary nature of the Pluto?CCharon pair. However, the captured objects remain on very elliptic orbits and the typical capture time is only ~ 100?years. In order to explain the origin of the small satellites of Pluto, we conjecture that some of these objects got disrupted during their Pluto-bound phase by a collision with a planetesimal of the disk. This could have generated a debris disk, which damped under internal collisional evolution, until turning itself into an accretional disk that could form small satellites on circular orbits, co-planar with Charon. Unfortunately, we find that objects large enough to carry a sufficient amount of mass to generate the small satellites of Pluto have collisional lifetimes orders of magnitude longer than the capture time. Thus, this scenario cannot explain the origin of the small satellites of Pluto, which remains elusive.     

Identification of the affected areas by mass movement through a physically based model of landslide hazard combined with an empirical model of debris flow

In tropical areas, mass movements are common phenomena, especially during periods of heavy rainfall, which frequently take place in the summer season. These phenomena have caused loss of life and serious damage to infrastructure and properties. The most prominent of these phenomena are landslides that can produce debris flows. Thus, this article aims at determining affected areas using a model to predict landslide prone areas (SHALSTAB) combined with an empirical model designed to define the debris flow travel distance and area of deposition. The methodology of this work consists of the following steps: (a) elaboration of a digital elevation model (DEM), (b) application of the deterministic SHALSTAB model to locate the landslide prone areas, (c) identification of the debris flow travel distance and area of deposition, and (d) mapping of the affected areas (landslides and debris flows). This work was developed in an area in which many mass movements occurred after intense rainfall during the summer season (February 1996) in the state of Rio de Janeiro, southeast Brazil. All of the scars produced by that event were mapped, allowing for validation of the applied models. The model results show that the mapped landslide locations can adequately be simulated by the model.     

Long-term analysis of rainfall-induced landslides in Umbria,central Italy

Natural Hazards - Analyses of historical records of landslides and climate variables are useful tools to search for correlations between damaging landslide events and their triggers. In this work,...