共查询到20条相似文献，搜索用时 31 毫秒
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Xu Zhang Ye Lu Yong-Heng Zhao National Astronomical Observatories Chinese Academy of Sciences Beijing Department of Physics Shandong University Jinan Department of Physics The University of Hong Kong Pokfulam Road Hong Kong 《中国天文和天体物理学报》2007,7(1):91-100
1 INTRODUCTION The classical problem of spherical accretion onto a compact object, e.g., a black hole or a neutron star (NS), has been studied by many authors. A hydrodynamical solution was presented by Bondi 1952, who showed that inside a certain capture… 相似文献
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Guo-Liang Lü 《中国天文和天体物理学报》2006,6(4):447-454
Using a population synthesis code, we have investigated the formation of symbiotic systems in which the hot component is a main-sequence star that is accreting matter from the cool component via Roche lobe overflow (RLOF). The RLOF can be divided into two cases: dynamically unstable and stable. In the first case, the birthrate of symbiotic stars is 0.056 yr-1 or 0.045 yr-1 depending on different assumptions; in the stable RLOF case, it is 0.002 yr-1 or 0.005 yr-1. The number of symbiotic stars with main-sequence accretors and unstable RLOF in our galaxy is about 5, that with stable RLOF is about 60 to 280. Comparison between our results with those of Yungelson et al. shows that symbiotic stars with MS accretors make only a small contribution ((?) 8%) to the whole population of symbiotic stars in the Galaxy. 相似文献
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Ye Lu Wei Wang Yong-Heng ZhaoNational Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2003,3(6):543-550
We examine the spectra of the persistent emission from anomalous X-ray pulsars (AXPs) and their variati on with the spin-down rate Ω. Based onan accretion-powered model, the influences of both the magnetic field and the mass accretion rate on the spectral properties of AXPs are addressed. We then investigate the relation between the spectral property of AXPs and mass accretion rate M. The result shows that there exists a linear correlation between the photon index and the mass accretion rate: the spectral hardness increases with increasing M. A possible emission mechanism for the explanation of the spectral properties of AXPs is also discussed. 相似文献
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Ying-He Zhao Zong-Yun Li Xiao-An Wu Qiu-He Peng Department of Astronomy Nanjing University Nanjing 《中国天文和天体物理学报》2005,5(6):601-609
We report on time-resolved spectroscopic observations of the SU Ursae Majoris dwarf nova, YZ Cnc for over 11 h on two nights during its 2002 January superoutburst. The spectra on the first day only showed absorption-line profiles, while on the second day the lines showed "W" profiles with blue and red troughs. The radial velocity curve of the absorption troughs and emission peaks of Hβ has an amplitude of 49±10 km s-1 and a phase offset of -0.07±0.04, which are very similar to those measured in quiescence. However, the γ velocity deviates strongly from the systemic velocity measured in quiescence, by some ±60 km s-1. Large shifts of -70 km s-1 in the orbital-averaged velocity and -0.09 in the phase are also found in our observations. All these features can be well explained by a precessing, eccentric disk. 相似文献
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Bhaskar Datta Arun V. Thampan Paul J. Wiita 《Journal of Astrophysics and Astronomy》1995,16(3-4):357-374
For accretion on to neutron stars possessing weak surface magnetic fields and substantial rotation rates (corresponding to
the secular instability limit), we calculate the disk and surface layer luminosities general relativistically using the Hartle
& Thorne formalism, and illustrate these quantities for a set of representative neutron star equations of state. We also discuss
the related problem of the angular momentum evolution of such neutron stars and give a quantitative estimate for this accretion
driven change in angular momentum. Rotation always increases the disk luminosity and reduces the rate of angular momentum
evolution. These effects have relevance for observations of low-mass X-ray binaries. 相似文献
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Arun V. Thampan & Bhaskar Datta 《Monthly notices of the Royal Astronomical Society》1998,297(2):570-578
We calculate the disc and boundary layer luminosities for accreting rapidly rotating neutron stars with low magnetic fields in a fully general relativistic manner. Rotation increases the disc luminosity and decreases the boundary layer luminosity. A rapid rotation of the neutron star substantially modifies these quantities as compared with the static limit. For a neutron star rotating close to the centrifugal mass shed limit, the total luminosity has contribution only from the extended disc. For such maximal rotation rates, we find that well before the maximum stable gravitational mass configuration is reached, there exists a limiting central density, for which particles in the innermost stable orbit will be more tightly bound than those at the surface of the neutron star. We also calculate the angular velocity profiles of particles in Keplerian orbits around the rapidly rotating neutron star. The results are illustrated for a representative set of equation of state models of neutron star matter. 相似文献
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T. A. Bell W. Whyatt S. Viti M. P. Redman 《Monthly notices of the Royal Astronomical Society》2007,382(3):1139-1144
We have carried out a systematic search for the molecular ion CO+ in a sample of eight protoplanetary and planetary nebulae in order to determine the origin of the unexpectedly strong HCO+ emission previously detected in these sources. An understanding of the HCO+ chemistry may provide direct clues for the physical and chemical evolution of planetary nebulae. We find that the integrated intensity of the CO+ line may be correlated with that of HCO+ , suggesting that the reaction of CO+ with molecular hydrogen may be an important formation route for HCO+ in these planetary nebulae. 相似文献
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The coherence of kilohertz quasi-periodic oscillations in the X-rays from accreting neutron stars 总被引：1，自引：0，他引：1
Didier Barret Jean-Francois Olive M. Coleman Miller 《Monthly notices of the Royal Astronomical Society》2006,370(3):1140-1146
We study in a systematic way the quality factor of the lower and upper kilohertz quasi-periodic oscillations (kHz QPOs) in a sample of low-luminosity neutron star X-ray binaries, showing both QPOs varying over a wide frequency range. The sample includes 4U 1636−536, 4U 1608−522, 4U 1735−44, 4U 1728−34, 4U 1820−303 and 4U 0614+09. We find that all sources except 4U 0614+09 show evidence of a drop in the quality factor of their lower kHz QPOs at high frequency. For 4U 0614+09 only the rising part of the quality factor versus frequency curve has been sampled so far. At the same time, in all sources but 4U 1728−34, the quality factor of the upper kHz QPO increases all the way to the highest detectable frequencies. We show that the high-frequency behaviours of both the lower and the upper kHz QPO quality factors are consistent with what is expected if the drop is produced by the approach of an active oscillating region to the innermost stable circular orbit: the existence of which is a key feature of general relativity in the strong field regime. Within this interpretation, our results imply gravitational masses around 2 M⊙ for the neutron stars in those systems. 相似文献
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The structure of accretion discs around magnetic T Tauri stars is calculated numerically using a particle hydrodynamical code, in which magnetic interaction is included in the framework of King's diamagnetic blob accretion model. Setting up the calculation so as to simulate the density structure of a quasi-steady disc in the equatorial plane of a T Tauri star, we find that the central star's magnetic field typically produces a central hole in the disc and spreads out the surface density distribution. We argue that this result suggets a promising mechanism for explaining the unusual flatness (IR excess) of T Tauri accretion disc spectra. 相似文献
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Application of a relativistic accretion disc model to X-ray spectra of LMC X-1 and GRO J1655-40 总被引：1，自引：0，他引：1
Marek Gierli&#;ski † rzej Macio&#;ek-Nied&#;wiecki Ken Ebisawa ‡ 《Monthly notices of the Royal Astronomical Society》2001,325(3):1253-1265
We present a general relativistic accretion disc model and its application to the soft-state X-ray spectra of black hole binaries. The model assumes a flat, optically thick disc around a rotating Kerr black hole. The disc locally radiates away the dissipated energy as a blackbody. Special and general relativistic effects influencing photons emitted by the disc are taken into account. The emerging spectrum, as seen by a distant observer, is parametrized by the black hole mass and spin, the accretion rate, the disc inclination angle and the inner disc radius.
We fit the ASCA soft-state X-ray spectra of LMC X-1 and GRO J1655-40 by this model. We find that, having additional limits on the black hole mass and inclination angle from optical/UV observations, we can constrain the black hole spin from X-ray data. In LMC X-1 the constraint is weak, and we can only rule out the maximally rotating black hole. In GRO J1655-40 we can limit the spin much better, and we find 0.68 a 0.88 . Accretion discs in both sources are radiation-pressure dominated. We do not find Compton reflection features in the spectra of any of these objects. 相似文献
We fit the ASCA soft-state X-ray spectra of LMC X-1 and GRO J1655-40 by this model. We find that, having additional limits on the black hole mass and inclination angle from optical/UV observations, we can constrain the black hole spin from X-ray data. In LMC X-1 the constraint is weak, and we can only rule out the maximally rotating black hole. In GRO J1655-40 we can limit the spin much better, and we find 0.68 a 0.88 . Accretion discs in both sources are radiation-pressure dominated. We do not find Compton reflection features in the spectra of any of these objects. 相似文献
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Mariano Méndez Michiel van der Klis 《Monthly notices of the Royal Astronomical Society》2000,318(3):938-942
We use data from the Rossi X-ray Timing Explorer to search for harmonics and sidebands of the two simultaneous kilohertz quasi-periodic oscillations (kHz QPOs) in Sco X-1. We do not detect any of these harmonics or sidebands, with 95 per cent confidence upper limits to their power between ∼1 and ∼10 per cent of the power of the upper kHz QPO. The oscillations produced at these frequencies may be attenuated in a scattering corona around the neutron star. We find that upper limits to the unattenuated power of some of the strongest theoretically predicted harmonics and sidebands are as low as ∼2 per cent of the unattenuated power of the high-frequency QPO in Sco X-1. 相似文献
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Hong-Xing Yin Cheng-Min Zhang Yong-Heng Zhao Li-Ming Song Fan Zhang National Astronomical Observatories Chinese Academy of Sciences Beijing Institute of High Energy Physics Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2005,5(6):595-600
For the bright neutron star low-mass X-ray binary Sco X-1, we analyzed all updated frequencies of the twin kilohertz quasi-periodic oscillations (kHz QPOs), their correlations and distributions. We found that the frequency separation of the kHz QPO peaks appears not to be a constant, rather, it decreases with increasing inferred mass accretion rate. We show that the currently available data of Sco X-1 by Rossi X-ray Timing Explorer are inconsistent with the proposals of the beat model that the frequency separation is a constant. Our conclusions are consistent with those of some previous researchers and we discuss further implications for the kilohertz QPO models. 相似文献