Numerical simulations of type III planetary migration – II. Inward migration of massive planets     

A. Pepli&#;ski  P. Artymowicz  G. Mellema 《Monthly notices of the Royal Astronomical Society》2008,386(1):179-198

We present a numerical study of rapid, so-called type III migration for Jupiter-sized planets embedded in a protoplanetary disc. We limit ourselves to the case of inward migration, and study in detail its evolution and physics, concentrating on the structure of the corotation and circumplanetary regions, and processes for stopping migration. We also consider the dependence of the migration behaviour on several key parameters. We perform this study using the results of global, two-dimensional hydrodynamical simulations with adaptive mesh refinement. The initial conditions are chosen to satisfy the condition for rapid inward migration. We find that type III migration can be divided into two regimes, fast and slow. The structure of the co-orbital region, mass accumulation rate and migration behaviour differ between these two regimes. All our simulations show a transition from the fast to the slow regime, ending type III migration well before reaching the star. The stopping radius is found to be larger for more massive planets and less massive discs. A sharp density drop is also found to be an efficient stopping mechanism. In the fast migration regime the migration rate and induced eccentricity are lower for less massive discs, but almost do not depend on planet mass. Eccentricity is damped on the migration time-scale.  相似文献   

Simulations of spiral galaxies with an active potential: molecular cloud formation and gas dynamics     

C. L. Dobbs  I. A. Bonnell 《Monthly notices of the Royal Astronomical Society》2008,385(4):1893-1902

We describe simulations of the response of a gaseous disc to an active spiral potential. The potential is derived from an N -body calculation and leads to a multi-armed time-evolving pattern. The gas forms long spiral arms typical of grand-design galaxies, although the spiral pattern is asymmetric. The primary difference from a grand-design spiral galaxy, which has a consistent two-/four-armed pattern, is that instead of passing through the spiral arms, gas generally falls into a developing potential minimum and is released only when the local minimum dissolves. In this case, the densest gas is coincident with the spiral potential, rather than offset as in the grand-design spirals. We would therefore expect no offset between the spiral shock and star formation, and no obvious corotation radius. Spurs which occur in grand-design spirals when large clumps are sheared off leaving the spiral arms, are rare in the active, time-evolving spiral reported here. Instead, large branches are formed from spiral arms when the underlying spiral potential is dissolving due to the N -body dynamics. We find that the molecular cloud mass spectrum for the active potential is similar to that for clouds in grand-design calculations, depending primarily on the ambient pressure rather than the nature of the potential. The largest molecular clouds occur when spiral arms collide, rather than by agglomeration within a spiral arm.  相似文献   

Radiative bubbles blown by slow stellar winds     

Christopher D. Matzner  Ruben Krasnopolsky 《Monthly notices of the Royal Astronomical Society》2008,386(2):903-908

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Hydrodynamical simulations of Galactic fountains – I. Evolution of single fountains     

C. Melioli  F. Brighenti  A. D'Ercole  E. M. de Gouveia Dal Pino 《Monthly notices of the Royal Astronomical Society》2008,388(2):573-586

The ejection of the gas out of the disc in late-type galaxies is related to star formation and is due mainly to Type II supernovae. In this paper, we studied in detail the development of the Galactic fountains in order to understand their dynamical evolution and their influence on the redistribution of the freshly delivered metals over the disc. To this aim, we performed a number of 3D hydrodynamical radiative cooling simulations of the gas in the Milky Way where the whole Galaxy structure, the Galactic differential rotation and the supernova explosions generated by a single OB association are considered. A typical fountain powered by 100 Type II supernovae may eject material up to ∼2 kpc which than collapses back mostly in the form of dense, cold clouds and filaments. The majority of the gas lifted up by the fountains falls back on the disc remaining within a radial distance  Δ R = 0.5 kpc  from the place where the fountain originated. This localized circulation of disc gas does not influence the radial chemical gradients on large scale, as required by the chemical models of the Milky Way which reproduce the metallicity distribution without invoking large fluxes of metals. Simulations of multiple fountains fuelled by Type II supernovae of different OB associations will be presented in a companion paper.  相似文献   

Newtonian non-linear hydrodynamics and magnetohydrodynamics     

Nicolaos K. Spyrou  Christos G. Tsagas 《Monthly notices of the Royal Astronomical Society》2008,388(1):187-196

We use covariant techniques to study the non-linear evolution of self-gravitating, non-relativistic media. The formalism is first applied to imperfect fluids, aiming at the kinematic effects of viscosity, before extended to inhomogeneous magnetized environments. The non-linear electrodynamic formulae are derived and successively applied to electrically resistive and to highly conductive fluids. By nature, the covariant equations isolate the magnetic effects on the kinematics and the dynamics of the medium, combining mathematical transparency and physical clarity. Employing the Newtonian analogue of the relativistic 1 + 3 covariant treatment also facilitates the direct comparison with the earlier relativistic studies and helps to identify the differences in an unambiguous way. The purpose of this work is to set the framework and take a first step towards the detailed analytical study of complex non-linear systems, like non-relativistic astrophysical plasmas and collapsing protogalactic clouds.  相似文献   

Vortical mechanism for generation of astrophysical jets     

M. G. Abrahamyan 《Astrophysics》2008,51(2):163-180

A vortical mechanism for generation of astrophysical jets is proposed based on exact solutions of the hydrodynamic equations with a generalized Rankine vortex. It is shown that the development of a Rankine vortex in the polar layer of a rotating gravitating body creates longitudinal fluxes of matter that converge toward the vortex trunk, providing an exponential growth in the angular rotation velocity of the trunk and a pressure drop on its axis. The increased rotational velocity of the vortex trunk and the on-axis pressure drop cease when the discontinuity in the azimuthal velocity at the surface of the trunk reaches the sound speed. During this time, ever deeper layers of the gravitating body are brought into the vortical motion, while the longitudinal velocity of the flow along the vortex trunk builds up, producing jet outflows of mass from its surface. The resulting vortices are essentially dissipationless. Dedicated to the 100-th birthday of Academician V. A. Ambartsumyan __________ Translated from Astrofizika, Vol. 51, No. 2, pp. 201–218 (May 2008).  相似文献   

Effects of intensive aquifers exploitation on groundwater salinity in coastal wetlands     

Malva Mancuso  Lucía Santucci  Eleonora Carol 《水文研究》2020,34(11):2313-2323

The coastal plain of the Río de la Plata constitutes a large wetland which develops on the right margin of the river estuary. Anthropic activities such as intensive exploitation of groundwater carried out in the vicinity of the wetland can modify the natural hydrological regime. The aim of this work is to asses the effects of intensive aquifer exploitation in coastal wetlands using hydrogeological models. Such models allow to evaluate changes in the environmental conditions of wetland at regional level. The hydrogeological model exposed in this work shows how the intensive groundwater exploitation affects the wetland area, generating important variations both in the groundwater flows and in the salinity of the groundwater. Identification of these modifications to the environment is important to generate guidelines leading to minimize these affectations.  相似文献   

Rotating accretion flows around black holes: convection and variability     

Igor V. Igumenshchev  Marek A. Abramowicz 《Monthly notices of the Royal Astronomical Society》1999,303(2):309-320

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On the boundary layer of accretion discs     

Carsten Obach  Wolfgang Glatzel 《Monthly notices of the Royal Astronomical Society》1999,303(3):603-610

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On the stability of viscous accretion tori     

R. Kleiber  W. Glatzel 《Monthly notices of the Royal Astronomical Society》1999,303(1):107-115

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