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81.
We present and discuss a short and simple derivation of orbital epicyclic frequencies for circular geodesic orbits in stationary
and axially symmetric spacetimes. Such spacetimes include as special cases analytically known black hole Kerr and Schwarzschild
spacetimes, as well as the analytic Hartle-Thorne spacetime and all numerically constructed spacetimes relevant for rotating
neutron stars. Our derivation follows directly from energy and angular momentum conservation and it uses the concept of the
effective potential. It has never been published, except for a few special cases, but it has already become a part of the
common knowledge in the field. 相似文献
82.
83.
84.
A. J. Keane † R. K. Barrett J. F. L. Simmons ‡ 《Monthly notices of the Royal Astronomical Society》2001,321(4):661-677
We examine the radial motion of a material particle in the intense radiation field of a static spherically symmetric compact object with spherical emitting surface outside the Schwarzschild radius. This paper generalizes previous work which dealt with radial motion in the Thomson limit, where the radiation force is simply proportional to the radiative flux. In the general case the average time component of the 4-momentum transferred to the particle is not negligible compared with its rest mass. Consequently, we find that the frequency dependence of the radiation force owing to Compton scattering for highly energetic photons gives rise to an increase in the effective mass of the test particle. In this work we outline the effects of this frequency dependence and compare these with the results in the Thomson limit. We present the frequency dependent saturation velocity curves for a range of stellar luminosities and radiation frequencies and present the resulting phase-space diagrams corresponding to the radial test particle trajectories. In particular, the stable equilibrium points which exist in the Thomson limit are found to be absent in the general case. 相似文献
85.
A. R. King J. E. Pringle D. T. Wickramasinghe 《Monthly notices of the Royal Astronomical Society》2001,320(3):L45-L48
On the basis of the current observational evidence, we put forward the case that the merger of two CO white dwarfs produces both a Type Ia supernova explosion and a stellar remnant, the latter in the form of a magnetar. The estimated occurrence rates raise the possibility that many, if not most, Type Ia supernovae might result from white dwarf mergers. 相似文献
86.
David Eichler 《Monthly notices of the Royal Astronomical Society》2002,335(4):883-886
87.
Rainer Hollerbach † Günther Rüdiger 《Monthly notices of the Royal Astronomical Society》2002,337(1):216-224
We consider the evolution of magnetic fields under the influence of Hall drift and Ohmic decay. The governing equation is solved numerically, in a spherical shell with r i / r o = 0.75 . Starting with simple free-decay modes as initial conditions, we then consider the subsequent evolution. The Hall effect induces so-called helicoidal oscillations, in which energy is redistributed among the different modes. We find that the amplitude of these oscillations can be quite substantial, with some of the higher harmonics becoming comparable with the original field. Nevertheless, this transfer of energy to the higher harmonics is not sufficient to accelerate significantly the decay of the original field, at least not at the R B = O (100) parameter values accessible to us, where this Hall parameter R B measures the ratio of the Ohmic time-scale to the Hall time-scale. We do find clear evidence though of increasingly fine structures developing for increasingly large R B , suggesting that perhaps this Hall-induced cascade to ever-shorter length-scales is eventually sufficiently vigorous to enhance the decay of the original field. Finally, the implications for the evolution of neutron star magnetic fields are discussed. 相似文献
88.
Patrizia A. Caraveo Giovanni F. Bignami Joachim E. Trümper 《Astronomy and Astrophysics Review》1996,7(3):209-216
Summary. As of today, seven X-ray sources have been tentatively identified as radio-quiet, isolated neutron stars. The family appears
to be a rapidly growing one, although not all the objects have been identified with the same degree of certainty. The most
convincing example of radio quiet pulsar is certainly Geminga, the neutron star nature of which, proposed in 1983 on the basis
of its similarity with the Vela pulsar, has been firmly established with the discovery of its X and pulsation. Four more neutron star candidates, originally found in the Einstein data, have been confirmed by ROSAT, which
has added to the list two more entries. All this is not the result of an unbiased search. The seven sources were not selected
at random: four are inside supernova remnants, an obvious place to search for isolated neutron stars, while the remaining
three were singled out because of some peculiarity. Intense -ray emission in the case of Geminga, very high X-ray counting rate for RXJ185635-3754, or being the brightest unidentified
source in the Einstein medium sensitivity survey, MS 0317-6647. In spite of the limited number of objects and of the observational
biases, these seven radio quiet neutron star candidates add valuable pieces of information to the observational panorama of
known pulsars. Their properties, inferred from the X-ray emission, offer a coherent picture, pointing towards thermally emitting,
cooling neutron stars.
Received: April 1, 1996 相似文献
89.
Ren-Xin Xu Hong-Guang Wang Guo-Jun QiaoDepartment of Astronomy School of Physics Peking University Beijing 《中国天文和天体物理学报》2002,2(6)
According to two estimated relations between the initial period andthe dynamo-generated magnetic dipole field of pulsars, we calculate the statisticaldistributions of pulsar initial periods. It is found that proto-pulsars are very likelyto have rotation periods between 20 ms and 30 ms, and that most of the pulsarsrotate initially at a period < 60 ms. Our result supports the asymmetric neutrinoemission model for pulsar kick. 相似文献
90.
Neophytos Messios Demetrios B. Papadopoulos Nikolaos Stergioulas 《Monthly notices of the Royal Astronomical Society》2001,328(4):1161-1168
Strong magnetic fields in relativistic stars can be a cause of crust fracturing, resulting in the excitation of global torsional oscillations. Such oscillations could become observable in gravitational waves or in high-energy radiation, thus becoming a tool for probing the equation of state of relativistic stars. As the eigenfrequency of torsional oscillation modes is affected by the presence of a strong magnetic field, we study torsional modes in magnetized relativistic stars. We derive the linearized perturbation equations that govern torsional oscillations coupled to the oscillations of a magnetic field, when variations in the metric are neglected (Cowling approximation). The oscillations are described by a single two-dimensional wave equation, which can be solved as a boundary-value problem to obtain eigenfrequencies. We find that, in the non-magnetized case, typical oscillation periods of the fundamental torsional modes can be nearly a factor of 2 larger for relativistic stars than previously computed in the Newtonian limit. For magnetized stars, we show that the influence of the magnetic field is highly dependent on the assumed magnetic field configuration, and simple estimates obtained previously in the literature cannot be used for identifying normal modes observationally. 相似文献