Large eddy simulations of thermal convection at high Rayleigh number     

Noä Cantin  Alain P. Vincent  & David A. Yuen 《Geophysical Journal International》2000,140(1):163-174

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On the migration of a system of protoplanets   总被引：1，自引：0，他引：1  

W. Kley † 《Monthly notices of the Royal Astronomical Society》2000,313(4):L47-L51

The evolution of a system consisting of a protoplanetary disc with two embedded Jupiter-sized planets is studied numerically. The disc is assumed to be flat and non-self-gravitating; this is modelled by the planar (two-dimensional) Navier–Stokes equations. The mutual gravitational interaction of the planets and the star, and the gravitational torques of the disc acting on the planets and the central star are included. The planets have an initial mass of one Jupiter mass M _Jup each, and the radial distances from the star are one and two semimajor axes of Jupiter, respectively.
During the evolution a joint wide annular gap is created by the planets. Both planets increase their mass owing to accretion of gas from the disc: after about 2500 orbital periods of the inner planet it has reached a mass of 2.3  M _Jup, while the outer planet has reached a mass of 3.2  M _Jup. The net gravitational torques exerted by the disc on the planets result in an inward migration of the outer planet on time-scales comparable to the viscous evolution time of the disc. The semimajor axis of the inner planet remains constant as there is very little gas left in its vicinity to induce any migration. When the distance of close approach eventually becomes smaller than the mutual Hill radius, the eccentricities increase strongly and the system may become unstable.
If disc depletion occurs rapidly enough before the planets come too close to each other, a stable system similar to our own Solar system may remain. Otherwise the orbits may become unstable and produce systems like υ And.  相似文献   

Galaxy destruction and diffuse light in clusters     

Carlos Calcáneo-Roldán  Ben Moore  Joss Bland-Hawthorn  David Malin  Elaine M. Sadler 《Monthly notices of the Royal Astronomical Society》2000,314(2):324-333

Deep images of the Centaurus and Coma clusters reveal two spectacular arcs of diffuse light that stretch for over 100 kpc, yet are just a few kiloparsecs wide. At a surface brightness of m _b ∼27–28 mag arcsec⁻² , the Centaurus arc is the most striking example known of structure in the diffuse light component of a rich galaxy cluster. We use numerical simulations to show that the Centaurus feature can be reproduced by the tidal debris of a spiral galaxy that has been tidally disrupted by the gravitational potential of NGC 4709. The surface brightness and narrow dimensions of the diffuse light suggest that the disc was corotating with its orbital path past pericentre. Features this prominent in clusters will be relatively rare, although at fainter surface brightness levels the diffuse light will reveal a wealth of structure. Deeper imaging surveys may be able to trace this feature for several times its presently observed extent, and somewhere along the tidal debris, a fraction of the original stellar component of the disc will remain bound, but transformed into a faint spheroidal galaxy. It should be possible to confirm the galactic origin of the Centaurus arc by observing planetary nebulae along its length with redshifts close to that of NGC 4709.  相似文献   

The black hole mass–galaxy age relation     

M. R. Merrifield  Duncan A. Forbes  A. I. Terlevich 《Monthly notices of the Royal Astronomical Society》2000,313(2):L29-L32

We present evidence that there is a significant correlation between the fraction of the mass of a galaxy that lies in its central black hole and the age of the galactic stellar population. Since the absorption-line indices that are used to estimate the age are luminosity-weighted, they essentially measure the time since the last significant episode of star formation in the galaxy. The existence of this correlation is consistent with several theories of galaxy formation, including the currently favoured hierarchical picture of galaxy evolution, which predicts just such a relation between the black hole mass and the time since the last burst of merger-induced star formation. It is not consistent with models in which the massive black hole is primordial, and hence uncoupled from the stellar properties of the galaxy.  相似文献   

On the magnetohydrodynamic decollimation in compact objects     

V. S. Beskin  I. Okamoto 《Monthly notices of the Royal Astronomical Society》2000,313(3):445-453

A simple analytical model of the particle-dominated outflow with zero total electric current from central rotating objects is considered. 'Exact' solutions for both relativistic and non-relativistic cases demonstrate the decollimation of the magnetic field lines in the region of the current closure. Such a decollimation can explain the presence of an energetic equatorial wind observed in many compact objects.  相似文献   

Galaxy clusters: oblate or prolate?     

Asantha R. Cooray 《Monthly notices of the Royal Astronomical Society》2000,313(4):783-788

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The IRAS PSCz dipole     

M. Rowan-Robinson  J. Sharpe  S. J. Oliver  O. Keeble  A. Canavezes  W. Saunders  A. N. Taylor  H. Valentine  C. S. Frenk  G. P. Efstathiou  R. G. McMahon  S. D. M. White  W. Sutherland  H. Tadros  S. Maddox 《Monthly notices of the Royal Astronomical Society》2000,314(2):375-397

We use the PSC z IRAS galaxy redshift survey to analyse the cosmological galaxy dipole out to a distance of 300  h ¹ Mpc. The masked area is filled in three different ways, first by sampling the whole sky at random, secondly by using neighbouring areas to fill a masked region, and thirdly using a spherical harmonic analysis. The method of treatment of the mask is found to have a significant effect on the final calculated dipole.
The conversion from redshift space to real space is accomplished by using an analytical model of the cluster and void distribution, based on 88 nearby groups, 854 clusters and 163 voids, with some of the clusters and all of the voids found from the PSC z data base.
The dipole for the whole PSC z sample appears to have converged within a distance of 200  h ¹ Mpc and yields a value for , consistent with earlier determinations from IRAS samples by a variety of methods. For b =1, the 2 range for ₀ is 0.431.02.
The direction of the dipole is within 13° of the cosmic microwave background (CMB) dipole, the main uncertainty in direction being associated with the masked area behind the Galactic plane. The improbability of further major contributions to the dipole amplitude coming from volumes larger than those surveyed here means that the question of the origin of the CMB dipole is essentially resolved.  相似文献   

The history of cosmic baryons: X-ray emission versus star formation rate     

N. Menci  A. Cavaliere 《Monthly notices of the Royal Astronomical Society》2000,311(1):50-62

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The observed evolution of galaxy clustering versus epoch-dependent biasing models     

M. Magliocchetti  J. S. Bagla  S. J. Maddox  O. Lahav 《Monthly notices of the Royal Astronomical Society》2000,314(3):546-556

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Magnetic flares and the optical variability of the X-ray transient XTE J1118+480     

A. Merloni  T. Di Matteo †  A. C. Fabian 《Monthly notices of the Royal Astronomical Society》2000,318(1):L15-L19

The simultaneous presence of a strong quasi-periodic oscillation, of period ∼10 s, in the optical and X-ray light curves of the X-ray transient XTE J1118+480 suggests that a significant fraction of the optical flux originates from the inner part of the accretion flow, where most of the X-rays are produced. We present a model of magnetic flares in an accretion disc corona where thermal cyclo-synchrotron emission contributes significantly to the optical emission, while the X-rays are produced by inverse Compton scattering of the soft photons produced by dissipation in the underlying disc and by the synchrotron process itself. Given the observational constraints, we estimate the values for the coronal temperature, optical depth and magnetic field intensity, as well as the accretion rate for the source. Within our model we predict a correlation between optical and hard X-ray variability and an anticorrelation between optical and soft X-rays. We also expect optical variability on flaring time-scales (∼tens of ms), with a power-density spectrum similar to that observed in the X-ray band. Finally, we use both the available optical/extreme-ultraviolet/X-ray spectral energy distribution and the low-frequency time variability to discuss limits on the inner radius of the optically thick disc.  相似文献