Tidal Disruption and Accretion of Planets and Brown Dwarfs Inside Giant Stars

A significant fraction of isolated white dwarfs host strong magnetic fields that range from a few to a thousand Megagauss. These high-field magnetic white dwarfs (HFMWDs) comprise ∼10% of all isolated white dwarfs. Remarkably, not a single close and detached binary system that is composed of a white dwarf and a low-mass-main-sequence star contains a HFMWD. If the origin of magnetic fields in white dwarfs were independent of binary interactions, then the observed distribution of isolated white dwarfs should be similar to those in detached binaries, yet they are not. Unless there is a mechanism by which distant companions prevent the formation of a strong magnetic field, a more plausible explanation is that highly magnetized white dwarfs became that way by engulfing (and removing) their companions. When a member of a binary system extends past its Roche-Lobe, mass transfer and tidal torques serve to distribute material in a circumbinary ‘envelope’ enclosing the system. This process causes the orbit to decay as the ambient material dynamically drags on the binary components. This interaction is referred to as common envelope evolution and is thought to be the primary channel for producing short-period binaries in the Universe. Using three-dimensional numerical simulations, we investigate common envelope events between an Asymptotic Giant Branch (AGB) star and low-mass companions that are expected to result in mergers. As a companion approaches the AGB core, it tidally disrupts. The disrupted material forms an accretion disk which may amplify, transport and anchor the magnetic field onto the proto-white dwarf. At the end of the AGB phase, a HFMWD would emerge

Accretion disks formed from tidally-disrupted companions inside AGB stars

The origin of isolated white dwarfs (WDs) with magnetic fields in excess of ∼1 MG has remained a mystery since their initial discovery. Recently, the formation of these high-field magnetic WDs has been observationally linked to binary interactions with low-mass companions (\u3c 0.1 solar mass ) during post- main-sequence evolution. Planetary and M dwarf companions orbiting within several AU of main-sequence stars will become engulfed during the primary’s expansion off the main sequence. Such low-mass companions rapidly in-spiral inside a “common envelope” until they are tidally disrupted near the natal white dwarf core. Formation of an accretion disk from the shredded companion provides a source of turbulence and shear which, in principle, acts to amplify magnetic fields and transport them to the WD surface. However, the disk is initially very cold (∼ 10^3 K) compared to the hot thermal bath present in the center of the red giant (∼ 10^7 K). As there is significant shear in the system, entrainment of hot stellar material into the cold disk may lead to vigorous mixing and thermal evaporation before the field can be sufficiently amplified. To study the evolution and lifetime of the tidally-disrupted disks, we perform three-dimensional hydrodynamic simulations of accretion disks formed from 1, 3, 6 and 10 Jupiter mass planets. While entrainment leads to a decrease in disk mass, we find that all disks survive long enough to sufficiently amplify the magnetic field

Mourning and storytelling in Walter Benjamin: A reading from the country of the lost ones

En “Desenterrar y recordar” Walter Benjamin se acerca al tema del recuerdo desde una metáfora singular: la excavación. Mas, lejos de ser solamente una actividad del orden de lo metafórico, excavar es en ocasiones la acción literal que ha de llevarse a cabo para encontrar pistas o claves que permitan resolver enigmas contemporáneos. En México, país donde —a partir del año 2007— los desaparecidos suman más de treinta mil, hombres y mujeres se han convertido en tiempos recientes en excavadores que, removiendo la tierra suelta, buscan sin descanso huellas o rastros de sus seres queridos. El saldo de la búsqueda ha sido de casi 1200 fosas clandestinas y más de tres mil cadáveres inhumados. ¿Qué hacer, pues, frente a tanta barbarie? Quizás acercándonos a la idea de narración de Benjamin, nos sea posible pensar el recuerdo en tanto desenterramiento como posibilidad de duelo en el país de los desaparecidosIn “Excavation and Memory” Walter Benjamin approaches the subject of remembering from a specific metaphor: excavation. But far from being only a metaphoric activity, excavation is sometimes the literal action with which to find clues to solve contemporary mysteries. In Mexico, country where since 2007 there are more than thirty thousand lost people, men and women have become recently excavators who, through loose soil, search without rest for footprints or traces of their loved ones. What is to be done with so much barbarity? Perhaps through the Benjamin’s notion of storytelling we could think of remembering in terms of unearthing as a possibility for mourning in the country of the lost one

Transient transformation meets gene function discovery: The strawberry fruit case

Beside the well known nutritional and health benefits, strawberry (Fragaria X ananassa) crop draws increasing attention as plant model system for the Rosaceae family, due to the short generation time, the rapid in vitro regeneration, and to the availability of the genome sequence of F. X ananassa and F. vesca species. In the last years, the use of high-throughput sequence technologies provided large amounts of molecular information on the genes possibly related to several biological processes of this crop. Nevertheless, the function of most genes or gene products is still poorly understood and needs investigation. Transient transformation technology provides a powerful tool to study gene function in vivo, avoiding difficult drawbacks that typically affect the stable transformation protocols, such as transformation efficiency, transformants selection, and regeneration. In this review we provide an overview of the use of transient expression in the investigation of the function of genes important for strawberry fruit development, defense and nutritional properties. The technical aspects related to an efficient use of this technique are described, and the possible impact and application in strawberry crop improvement are discussed

3-D structure of the crust and uppermost mantle at the junction between the Southeastern Alps and External Dinarides from ambient noise tomography

3noWe use ambient noise tomography to investigate the crust and the uppermost mantle structure beneath the junction between the Southern Alps, the Dinarides and the Po Plain. We obtained Rayleigh wave empirical Green's functions from cross-correlation of vertical component seismic recordings for three years (2010-2012) using stations from networks in Italy, Slovenia, Austria, Croatia, Serbia and Switzerland. We measure group and phase velocity dispersion curves from the reconstructed Rayleighwaves in the period range 5-30 and 8-37 s, respectively, andwe invert the surfacewave velocities for tomographic images on a grid of 0.1° ×0.1°. After the tomography, the group velocities are then inverted to compute the 3-D shear wave velocity model of the crust and the upper mantle beneath the region. Our shear wave velocity model provides the 3-D image of the structure in the region between Northeastern Italy, Slovenia and Austria. The velocity variations at shallow depths correlate with known geological and tectonic domains. We find low velocities below the Po Plain, the northern tip of the Adriatic and the Pannonian Basin, whereas higher velocities characterize the Alpine chain. The vertical cross-sections reveal a clear northward increase of the crustal thickness with a sharp northward dipping of the Moho that coincides at the surface with the leading edge of the Alpine thrust front adjacent to the Friuli Plain in Northeastern Italy. This geometry of the Moho mimics fairly well the shallow north dipping geometry of the decollement inferred from permanent GPS velocity field where high interseismic coupling is reported. From the northern Adriatic domain up to the Idrija right lateral strike-slip fault system beneath Western Slovenia, the crustal thickness is more uniform. Right across Idrija fault, to the northeast, and along its strike, we report a clear change of the physical properties of the crust up to the uppermost mantle as reflected by the lateral distribution of both group and phase velocity anomalies at relevant periods. Idrija fault is therefore interpreted as a subvertical fault sampling the whole crust. Our 3-D velocity model favours crustal thickening with Adria underthrusting the Alps at a shallow angle north of the Friuli Plain where much of the convergence is absorbed and where the destructive 1976 M s 6.5 thrust Friuli earthquake sequence took place. In Western Slovenia, the deformation is accommodated by strike-slip motion along the Idrija strike-slip fault system where the destructive 1511 M w 6.9 right lateral strike-slip event occurred.partially_openopenGuidarelli, Mariangela; Aoudia, Abdelkrim; Costa, GiovanniGuidarelli, Mariangela; Aoudia, Abdelkrim; Costa, Giovann

Symmetry defects in single-gyre, wind-driven oceanic systems

We explore some symmetry properties of the leading terms that constitute the solution describing the flow field structure in a wind-driven, bottom-dissipated ocean. Both the weakly non-linear and the highly non-linear regime are investigated. The main result is that the northward displacement and the westward intensification of the current system, which are typical of the subtropical gyres (for instance the North Atlantic Ocean), can be ascribed to an interplay between the symmetries of these terms. Moreover, a duality relationship allows us to relate the conclusions concerning one regime to the other