Deux ou trois choses que l'on savait dans la France de l'Ouest, en 2001, a propos de la nature de certaines structures funéraires dites monumentales, ainsi que leur ordonnancement chronologique au long des Ve et IVe millenaires

On donne ici des résultats récents sur les monuments mégalithiques du Morbihan (site de Lannec Er Gadouer), et quelques idées sur la monumentalité funéraire et le Néolithique des régiones atlantiques

The viscosity of Miranda

Voyager 2 images of Miranda revealed a significant history of geological activity. Overlying an apparently ancient cratered terrain are assemblages of concentric ridges, scarps, and dark banded material. The problems that evolutionary thermal and structural modes of Miranda must face, to provide a convincing explanation for such topographic complexity, are examined

The potential for tidally heated icy and temperate moons around exoplanets

Moons of giant planets may represent an alternative to the classical picture of habitable worlds. They may exist within the circumstellar habitable zone of a parent star, and through tidal energy dissipation they may also offer alternative habitable zones, where stellar insolation plays a secondary, or complementary, role. We investigate the potential extent of stable satellite orbits around a set of 74 known extrasolar giant planets located beyond 0.6 AU from their parent stars - where moons should be long-lived with respect to removal by stellar tides. Approximately 60% of these giant planets can sustain satellites or moons in bands up to $\sim 0.04$ AU in width. For comparison, the Galiean satellites extend to $\sim 0.013$ AU. We investigate the stellar insolation that moons would experience for these exoplanet systems, and the implications for sublimation loss of volatiles. We find that between 15 and 27% of {\em all} known exoplanets may be capable of harboring small, icy, moons. In addition, some 22-28% of all known exoplanets could harbor moons within a ``sublimation zone'', with insolation temperatures between 273 K and 170 K. A simplified energy balance model is applied to the situation of temperate moons, maintained by a combination of stellar insolation and tidal heat flow. We demonstrate that large moons ($>0.1$M$_{\oplus}$), at orbital radii commensurate with those of the Galilean satellites, could maintain temperate, or habitable, surface conditions during episodes of tidal heat dissipation of the order 1-100 times that currently seen on Io. (Abridged).Comment: 28 pages, 8 Figures, AASTex, Accepted for publication in the Astrophysical Journa

De la construction a la reconstruction, en passant par la ruine. Une synthese archeologique autour de la barre de steles du gran menhir et la tombe a couloir de la table des marchands (Locmariaquer, Morbihan, France)

Con este artículo, se pretende ofrecer una síntesis de las diferentes fases de ocupación del entorno arqueológico del Grand Menhir y la Table des Marchands (Locmariaquer, Morbihan, Francia). Se realiza así un recorrido por la evolución del sitio basándose en los datos que han proporcionado las diferentes excavaciones desarrolladas en el lugar y los análisis de laboratorio más recientes. Hay que destacar no obstante que las diferentes fases de ocupación no tienen por qué ser sinónimo de etapas constructivas. Por ello, la Fase 0 correspondería a la ocupación previa del lugar antes de la erección de las primeras arquitecturas monumentales. Se caracteriza por la presencia en el paleosuelo de industria lítica mesolítica (al igual que ocurre en otros túmulos de la zona) y de los primeros restos de cerámica, que marcan la transición a sociedades de carácter agrícola en torno al VI-V milenio a.C. La Fase 1, durante el V milenio a.C, vendría marcada por la creación de hasta tres posibles líneas o barras de estelas monumentales, constatadas en las excavaciones arqueológicas por la presencia de fosas de cimentación y de una estela integrada en la tumba de corredor posterior. Por su parte, la Fase 2 supondría la caída de estas estelas neolíticas. Los datos arqueológicos (líneas de fractura, disposición de los fragmentos del Grand Menhir...) apuntan a una caída accidental y consecutiva, que invita a plantear la hipótesis de un seísmo como causa más factible. Las fosas que habrían quedado vacías se rellenan de sedimento correspondiente a ocupaciones del Castellic, mientras que los ortostatos conservados se extrajeron para ser reutilizados en la construcción de los monumentos de Table des Marchands o Er Gran. La Fase 3 corresponde a la erección de la tumba de corredor de Table des Marchands y de su túmulo, que sufrió una ampliación posterior. La Fase 4 viene definida por la ruina y destrucción del monumento a lo largo de finales del IV milenio a.C. y principios del III. En fases posteriores se constatan ciertas frecuentaciones del lugar durante la Edad del Bronce, época galorromana y siglos modernos. Finalmente, la Fase 5 correspondería a las excavaciones arqueológicas que se han ido desarrollando en el área desde el siglo XVIII

Sels de mer, sels de terre. Indices et preuves de fabrication du sel sur le rivages de l'Europe Occidentale, du Ve au IIIe millénaire

On donne ici quelques reflexions sur l'exploitation de sel dès le Néolithique et sa valeur comme source de richesse et prestige. Sont analysés quelques exemples etnographiques et historiques d'obtention de ce produit, en les comparant avec quelques traces archéologiques dans différents lieux de l'Europe

Equilibria of a Self-Gravitating, Rotating Disk Around a Magnetized Compact Object

We examine the effect of self-gravity in a rotating thick-disk equilibrium in the presence of a dipolar magnetic field. In the first part, we find a self-similar solution for non-self-gravitating disks. The solution that we have found shows that the pressure and density equilibrium profiles are strongly modified by a self-consistent toroidal magnetic field. We introduce 3 dimensionless variables $C_B$, $C_c$, $C_t$ that indicate the relative importance of toroidal component of magnetic field ($C_B$), centrifugal ($C_c$) and thermal ($C_t$) energy with respect to the gravitational potential energy of the central object. We study the effect of each of them on the structure of the disk. In the second part, we investigate the effect of self-gravity on the these disks; thus we introduce another dimensionless variable ($C_g$) that shows the importance of self-gravity. We find a self-similar solution for the equations of the system. Our solution shows that the structure of the disk is modified by the self-gravitation of the disk, the magnetic field of the central object, and the azimuthal velocity of the gas disk. We find that self-gravity and magnetism from the central object can change the thickness and the shape of the disk. We show that as the effect of self-gravity increases the disk becomes thinner. We also show that for different values of the star's magnetic field and of the disk's azimuthal velocity, the disk's shape and its density and pressure profiles are strongly modified.Comment: 7 page with 6 figures, Accepted for MNRA

Amplification of MHD waves in swirling astrophysical flows

Recently it was found that helical magnetized flows efficiently amplify Alfv\'en waves (Rogava et al. 2003, A&A, v.399, p.421). This robust and manifold nonmodal effect was found to involve regimes of transient algebraic growth (for purely ejectional flows), and exponential instabilities of both usual and parametric nature. However the study was made in the incompressible limit and an important question remained open - whether this amplification is inherent to swirling MHD flows per se and what is the degree of its dependence on the incompressibility condition. In this paper, in order to clear up this important question, we consider full compressible spectrum of MHD modes: Alfv\'en waves (AW), slow magnetosonic waves (SMW) and fast magnetosonic waves (FMW). We find that helical flows inseparably blend these waves with each other and make them unstable, creating the efficient energy transfer from the mean flow to the waves. The possible role of these instabilities for the onset of the MHD turbulence, self-heating of the flow and the overall dynamics of astrophysical flows are discussed.Comment: 8 pages, 9 figures, accepted for publication (18.03.2003) in the "Astronomy and Astrophysics

Vertically Self-Gravitating ADAFs in the Presence of Toroidal Magnetic Field

Force due to the self-gravity of the disc in the vertical direction is considered to study its possible effects on the structure of a magnetized advection-dominated accretion disc. We present steady-sate self similar solutions for the dynamical structure of such a type of the accretion flows. Our solutions imply reduced thickness of the disc because of the self-gravity. It also imply that the thickness of the disc will increase by adding the magnetic field strength.Comment: Accepted for publication in Astrophysics and Space Science

On type-I migration near opacity transitions. A generalized Lindblad torque formula for planetary population synthesis

We give an expression for the Lindblad torque acting on a low-mass planet embedded in a protoplanetary disk that is valid even at locations where the surface density or temperature profile cannot be approximated by a power law, such as an opacity transition. At such locations, the Lindblad torque is known to suffer strong deviation from its standard value, with potentially important implications for type I migration, but the full treatment of the tidal interaction is cumbersome and not well suited to models of planetary population synthesis. The expression that we propose retains the simplicity of the standard Lindblad torque formula and gives results that accurately reproduce those of numerical simulations, even at locations where the disk temperature undergoes abrupt changes. Our study is conducted by means of customized numerical simulations in the low-mass regime, in locally isothermal disks, and compared to linear torque estimates obtained by summing fully analytic torque estimates at each Lindblad resonance. The functional dependence of our modified Lindblad torque expression is suggested by an estimate of the shift of the Lindblad resonances that mostly contribute to the torque, in a disk with sharp gradients of temperature or surface density, while the numerical coefficients of the new terms are adjusted to seek agreement with numerics. As side results, we find that the vortensity related corotation torque undergoes a boost at an opacity transition that can counteract migration, and we find evidence from numerical simulations that the linear corotation torque has a non-negligible dependency upon the temperature gradient, in a locally isothermal disk.Comment: Appeared in special issue of "Celestial Mechanics and Dynamical Astronomy" on Extrasolar Planetary System

Selected Papers on Protoplanetary Disks

Three papers present studies of thermal balances, dynamics, and electromagnetic spectra of protoplanetary disks, which comprise gas and dust orbiting young stars. One paper addresses the reprocessing, in a disk, of photons that originate in the disk itself in addition to photons that originate in the stellar object at the center. The shape of the disk is found to strongly affect the redistribution of energy. Another of the three papers reviews an increase in the optical luminosity of the young star FU Orionis. The increase began in the year 1936 and similar increases have since been observed in other stars. The paper summarizes astronomical, meteoric, and theoretical evidence that these increases are caused by increases in mass fluxes through the inner portions of the protoplanetary disks of these stars. The remaining paper presents a mathematical-modeling study of the structures of protostellar accretion disks, with emphasis on limits on disk flaring. Among the conclusions reached in the study are that (1) the radius at which a disk becomes shadowed from its central stellar object depends on radial mass flow and (2) most planet formation has occurred in environments unheated by stellar radiation