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111.
具有硅酸盐尘埃特征碳星的新的候选者 总被引:1,自引:1,他引:0
本文根据红外天文卫星的宽波段测光及低分辨率光谱资料,给出了两颗新的可能具有硅酸尘埃特征的碳星及4颗可能的候选者。 相似文献
112.
To accomplish its mission, the spaceborne observatory SNAP (SuperNova Acceleration Probe) requires a pointing stability of
<0.03 arcseconds during exposures lasting up to 500 sec. A Monte Carlo simulation of the photoelectron statistics from the
guiding star investigates geometrical (such as the pixel size of the detector or the plate scale) and physical parameters
(such as the magnitude of the star). It is shown that simple centroiding calculations can lead to the desired accuracy with
guide stars as faint as magnitude 16. Availability of these stars is verified thanks to the HST Guide Star Catalog complemented
with a statistical model of the distribution of stars. Thus a through-the-lens sensor that uses stars as faint as magnitude
16 to provide the necessary guiding signals is feasible.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
113.
David Eichler 《Monthly notices of the Royal Astronomical Society》2002,335(4):883-886
114.
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
115.
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
116.
Guillermo Bosch † Elena Terlevich ‡ Roberto Terlevich § 《Monthly notices of the Royal Astronomical Society》2002,329(3):481-496
We have obtained accurate CCD narrow-band Hβ and Hα photometry of giant H ii regions (GEHRs) in M33, NGC 6822 and M101. Comparison with previous determinations of emission-line fluxes shows large discrepancies; their probable origins are discussed. Combining our new photometric data with global velocity dispersion ( σ ) derived from emission linewidths, we review the relation. A re-analysis of the properties of the GEHRs included in our sample shows that age spread and the superposition of components in multiple regions introduce a considerable spread in the regression. Combining the information available in the literature regarding ages of the associated clusters, evolutionary footprints on the interstellar medium, and kinematical properties of the knots that build up the multiple GEHRs, we find that a subsample – which we refer to as young and single GEHRs – do follow a tight relation in the plane. 相似文献
117.
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
118.
Comparisons of Infrared Colors and Emission-line Intensities between Two types of Seyfert 2 Galaxies
We study the relation between the infrared colors[ OⅢ] emission lines,gaseous absorbing column density(NH) ,and the detectability of the polarized (hidden)broad-line region(HBLR) in a large sample of 75 Seyfert 2 galaxies(Sy2s).From the indicators of star-formation activity,f60/f100 and LFIR/LB,we find some evidence that the Sy2s without HBLR show higher star-formation activities than those with HBLR,in agreement with previous prediction.Also,we confirm that the HBLR Sy2s tend to have a larger luminosity ratio of the core to the host galaxy,suggesting that the HBLR Sy2s display more powerful AGN activity.Howerver,the level of obscuration found in previous papers in nearly indistinguishable between the two types of Sy2s.The results support the statement that the non-HBLR Sy2s,with a weaker core component and a stronger star-formation activity component,are intrinsically different from the HBLR Sy2s,which are Sy1 systems with a hidden powerful AGN core and a low star-formation activity.The indications are that the non-HBLR Sy2s might be at an earlier evolutionary phase than the HBLR Sy2s. 相似文献
119.
Søren S. Larsen Duncan A. Forbes Jean P. Brodie 《Monthly notices of the Royal Astronomical Society》2001,327(4):1116-1126
We explore the rich globular cluster (GC) system of the nearby Sa galaxy M104, the 'Sombrero' (NGC 4594), using archive Wide Field Planetary Camera 2 data. The GC colour distribution is found to be bimodal at the >99 per cent confidence level, with peaks at and . The inferred metallicities are very similar to those of GCs in our Galaxy and M31. However, the Sombrero reveals a much enhanced number of red (metal-rich) GCs compared to other well-studied spirals. Because the Sombrero is dominated by a huge bulge and only has a modest disc, we associate the two subpopulations with the halo and bulge components, respectively. Thus our analysis supports the view that the metal-rich GCs in spirals are associated with the bulge rather than with the disc. The Sombrero GCs have typical effective (half-light) radii of ∼2 pc with the red ones being ∼30 per cent smaller than the blue ones. We identify many similarities between the GC system of the Sombrero and those of both late-type spirals and early-type galaxies. Thus both the GC system and the Hubble type of the Sombrero galaxy appear to be intermediate in their nature. 相似文献
120.
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