Dynamical Evolution of Barred Galaxies     

E. Athanassoula 《Celestial Mechanics and Dynamical Astronomy》2005,91(1-2):9-31

Angular momentum redistribution within barred galaxies drives their dynamical evolution. Angular momentum is emitted mainly by near-resonant material in the bar region and absorbed by resonant material mainly in the outer disc and in the halo. This exchange determines the strength of the bar, the decrease of its pattern speed, as well as its morphology. If the galaxy has also a gaseous component and/or a companion or satellite, then these also take part in the angular momentum exchange. During the evolution a bar structure forms in the inner parts of the halo as well. This bar is shorter and fatter than the disc bar and stays so all through the simulation, although its length grows considerably with time. Viewed edge-on, the bar in the disc component acquires a boxy or peanut shape. I describe the families of periodic orbits that explain such structures and review the observations showing that boxy/peanut ‘bulges’ are in fact just bars seen edge-on.  相似文献   

The baseline intracluster entropy profile from gravitational structure formation     

G. Mark Voit  Scott T. Kay  Greg L. Bryan 《Monthly notices of the Royal Astronomical Society》2005,364(3):909-916

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Evolution of the velocity field in model potentials     

V. V. Orlov 《Astronomy Letters》2005,31(7):494-499

We consider the evolution of the structure of the velocity field formed by the loops of the trajectory in a generalized Hénon-Heiles model potential. Box-shaped orbits alternating with periodic trajectories are shown to dominate at low values of the energy integral. Signatures of shell-and tube-shaped structures appear as the energy increases. Tube-shaped orbits are associated with stable periodic trajectories with small resonance ratios. Zones of stochastic orbits appear at values of the energy integral close to its critical value, which corresponds to the opening of the zero-velocity contour.  相似文献   

Hilda asteroids among Jupiter family comets     

Romina P. Di Sisto  Adrián Brunini  Lorena D. Dirani  Rosa B. Orellana 《Icarus》2005,174(1):81-89

Hilda asteroids and comets are similar from the compositional point of view. The D-taxonomic class prevailing among Hildas has all the characteristics found in cometary spectra. Jupiter Family Comets (JFCs) coming from the trans-neptunian region are under the gravitational control of Jupiter, making them a dynamically unstable population with a mean dynamical lifetime of 10⁴ to ¹⁰⁵ years. In contrast, Hilda asteroids residing in the 3:2 mean motion resonance with Jupiter are a very stable population. But once they escape from the resonance, they are dynamically controlled by Jupiter, and in this sense their behavior resembles that of JFC. We performed a numerical simulation to analyze the dynamical evolution that Hildas follow after escaping from the resonance, and their contribution to the JFC population. We found that 8% of the particles leaving the resonance end up impacting Jupiter. 98.7% of the escaped Hildas live at least 1000 years as a JFC, with a mean lifetime of 1.4×¹⁰⁶ years. In particular, escaped Hildas stay mainly in the region of perihelion distances greater than 2.5 AU. On the other hand, the number of escaped Hildas reaching the inner Solar System (q<2.5 AU) is negligible. So, there are almost no Hilda asteroids among the NEO population. We also analyzed the possibility that the Shoemaker-Levy 9 were an escaped Hilda asteroid. In this case, it would be possible to give stronger constraints to its pre-capture orbital elements.  相似文献   

Rotational evolution of protoneutron stars with hyperons: spin up or not?     

Y.-F. Yuan  Jeremy S. Heyl † 《Monthly notices of the Royal Astronomical Society》2005,360(4):1493-1505

We study the evolution of a rigidly rotating protoneutron star (PNS) with hyperons and nucleons or solely nucleons in its core due to the escape of trapped neutrinos. As the neutrinos escape, the core nucleonic neutron star (NS) expands and the stellar rotation slows. After the neutrinos escape, the range of the spin periods is narrower than the initial one, but the distribution is still nearly uniform. A PNS with hyperons, at the late stage of its evolution, keeps shrinking and spinning up until all the trapped neutrinos escape. Consequently, the distribution of the stellar initial spin periods is skewed towards shorter periods. If the hyperonic star is metastable, its rotational frequency accelerates distinguishedly before it collapses to a black hole.  相似文献   

Morphological studies of the Spitzer Wide-Area Infrared Extragalactic survey galaxy population in the UGC 10214 Hubble Space Telescope/Advanced Camera for Surveys field     

E. Hatziminaoglou  P. Cassata  G. Rodighiero  I. Pérez-Fournon  A. Franceschini  A. Hernán-Caballero  F. M. Montenegro-Montes  A. Afonso-Luis  T. Jarrett  G. Stacey  C. Lonsdale  F. Fang  S. Oliver  M. Rowan-Robinson  D. Shupe  H. E. Smith  J. Surace  C. K. Xu  E. A. González-Solares 《Monthly notices of the Royal Astronomical Society》2005,364(1):47-58

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The ages and metallicities of galaxies in the local universe     

Anna Gallazzi  Stéphane Charlot  Jarle Brinchmann  Simon D. M. White  Christy A. Tremonti 《Monthly notices of the Royal Astronomical Society》2005,362(1):41-58

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Near-infrared K-band imaging of a sample of ultra-steep-spectrum radio sources selected at 74 MHz   总被引：1，自引：0，他引：1  

Matt J. Jarvis  Maria J. Cruz  Aaron S. Cohen  Huub J. A. Röttgering  Namir E. Kassim 《Monthly notices of the Royal Astronomical Society》2004,355(1):20-30

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Confusion noise at far-infrared to millimetre wavelengths     

M. Negrello  M. Magliocchetti  L. Moscardini  G. De Zotti  G. L. Granato  L. Silva 《Monthly notices of the Royal Astronomical Society》2004,352(2):493-500

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A source of high-velocity white dwarfs     

Melvyn B. Davies  rew King  Hans Ritter 《Monthly notices of the Royal Astronomical Society》2002,333(2):463-468

We investigate whether the recently observed population of high-velocity white dwarfs can be derived from a population of binaries residing initially within the thin disc of the Galaxy. In particular, we consider binaries where the primary is sufficiently massive to explode as a Type II supernova. A large fraction of such binaries are broken up when the primary then explodes as a supernova, owing to the combined effects of the mass loss from the primary and the kick received by the neutron star on its formation. For binaries where the primary evolves to fill its Roche lobe, mass transfer from the primary leads to the onset of a common envelope phase during which the secondary and the core of the primary spiral together as the envelope is ejected. Such binaries are the progenitors of X-ray binaries if they are not broken up when the primary explodes. For those systems that are broken up, a large number of the secondaries receive kick velocities ∼100–200 km s⁻¹ and subsequently evolve into white dwarfs. We compute trajectories within the Galactic potential for this population of stars and relate the birth rate of these stars over the entire Galaxy to those seen locally with high velocities relative to the local standard of rest (LSR) . We show that for a reasonable set of assumptions concerning the Galactic supernova rate and the binary population, our model produces a local number density of high-velocity white dwarfs compatible with that inferred from observations. We therefore propose that a population of white dwarfs originating in the thin disc may make a significant contribution to the observed population of high-velocity white dwarfs.  相似文献