中子星中心致密天体的双星起源          下载免费PDF全文

刁振琪  王德华  叶长青 《天文学报》2020,61(5):56

探讨了认为中心致密天体(CCO)起源于双星的可能性.首先, CCO与正常遗迹脉冲星有着相似的平均自旋周期,但CCO的平均表面磁场强度(B～5.4×10~(10)Gs)低于正常遗迹脉冲星(B～7.7×10~(12)Gs)～2个量级.同时,几乎所有的正常遗迹脉冲星均分布在爱丁顿吸积加速线以上,而CCO全部分布在自旋加速线以下.因此怀疑CCO可能起源于双星吸积加速过程.其次,基于中子星再加速理论,分析了CCO可能的双星演化过程:双星系统中, CCO以M～1017g·s~(-1)的吸积率,经过～106yr的时间共吸积△M～10~(-2)M⊙的物质,其自旋周期将会从P～10 s降低至P～0.1 s,表面磁场强度将会从B～10~(12)Gs降低至B～1010Gs.考虑到～106yr的演化时标远大于CCO遗迹的年龄(～0.3–7 kyr),猜想CCO可能是双星系统中第1颗恒星超新星爆发的产物,而第2颗恒星超新星爆发后双星解体,留下CCO和第2颗恒星的超新星遗迹.该模型预言在CCO附近可能存在一颗年轻的正常脉冲星(P～0.02 s, B～1012Gs),并期望未来的射电望远镜和高能探测器能够进行搜寻.  相似文献   

大气海洋环境数值模拟中的若干计算问题   总被引：1，自引：0，他引：1  

季仲贞  王斌  曾庆存 《气候与环境研究》1999,4(2):135-151

为了适应发展气候数值模拟和环境数值模拟的需要,综合介绍了与此密切有关的若干计算问题。首先,指出这类问题易于出现计算紊乱、非物理解和非线性计算不稳定,同时,简要介绍造成这些问题出现的三种机理：虚假频散、能量关系破坏和能谱的非线性转移。然后,把这类问题归结为一种“发展方程”,给出了与此有关的几个定理,阐述了计算稳定性、能量守恒性和算子非负性之间的密切关系。接着,分别介绍了多种完全平方守恒的差分格式的构造方法,其中包括隐式的和显式的完全平方守恒的差分格式,高时间精度和高阶紧致的完全平方守恒的差分格式,同时也给出若干具体算例说明这些格式的计算效果。最后,对全文作了小结,并指出今后应进一步研究的若干重要问题。  相似文献   

Global velocity field and bubbles in the blue compact dwarf galaxy Mrk 86     

A. Gil de Paz  J. Zamorano  J. Gallego 《Monthly notices of the Royal Astronomical Society》1999,306(4):975-987

We have studied the velocity field of the blue compact dwarf galaxy Mrk 86 (NGC 2537) using data provided by 14 long-slit optical spectra obtained in 10 different orientations and positions. This kinematical information is complemented with narrow-band ([O  iii ]5007 Å and H α ) and broad-band ( B , V , Gunn r and K ) imaging. The analysis of the galaxy global velocity field suggests that the ionized gas could be distributed in a rotating inclined disc, with projected central angular velocity of Ω=34 km s⁻¹ kpc⁻¹. The comparison between the stellar, H  i and modelled dark matter density profile indicates that the total mass within its optical radius is dominated by the stellar component. Peculiarities observed in its velocity field can be explained by irregularities in the ionized gas distribution or local motions induced by star formation.
Kinematical evidences for two expanding bubbles, Mrk 86–B and Mrk 86–C, are given. They show expanding velocities of 34 and 17 km s⁻¹, H α luminosities of 3×10³⁸ and 1.7×10³⁹ erg s⁻¹, and physical radii of 374 and 120 pc, respectively. The change in the [S  ii ]/H α , [N  ii ]/H α , [O  ii ]/[O  iii ] and [O  iii ]/H β line ratios with the distance to the bubble precursor suggests a diminution in the ionization parameter and, in the case of Mrk 86–B, an enhancement of the shock-excited gas emission. The optical–near-infrared colours of the bubble precursors are characteristic of low‐metallicity star‐forming regions (∼0.2 Z_⊙) with burst strengths of about 1 per cent in mass.  相似文献   

Conformally coupled Abelian gauged Q balls     

C. Wolf 《Astronomische Nachrichten》1990,311(5):277-282

A conformally coupled Abelian gauged Q ball is studied in curved space. The mass of the Q ball is calculated in terms of the conserved Q charge and the parameters in the lagrangian and a brief discussion is given on the effects produced by the conformal couplings.  相似文献   

铵盐镍基电镀金刚石钻头     

王群英  杨凯华 《地质科技情报》2007,26(4):82-84

探讨了在普通镀镍溶液中加入铵离子后,电镀液成分和电镀工艺条件对镀层性能的影响,得到了一种用于钻进坚硬致密弱研磨性岩层的优化配方及工艺条件,讨论了铵离子引起的络合作用.实验表明,当氯化铵的质量浓度为18 g/L时可细化镀层晶粒,提高胎体的硬度和脆性,改变胎体与金刚石的包镶程度,从而改变电镀金刚石钻头的性能,得到一种能有效钻进坚硬致密弱研磨性岩石的新性能电镀金刚石钻头.  相似文献   

Star-forming regions in blue compact dwarf galaxies     

Richard I.Davies  HajimeSugai  Martin J.Ward 《Monthly notices of the Royal Astronomical Society》1998,295(1):43-54

We present near-infrared 2.1-μm continuum and Brγ and 1–0S(1) line images of three blue compact dwarf galaxies: II Zw 40, NGC 5253 and He 2-10. Comparison of the morphologies of the emission-line regions and continuum together with the line ratios shows that in these cases the starbursts are typified by strongly peaked Brγ and weak diffuse H₂ emission, indicating the presence of one or more compact nuclei, and also tidal tails. We consider the possible origins of the H₂ emission, and conclude that shock excitation in cloud collisions, and hence dynamical processes such as interactions or mergers, is important. By comparing models of the equivalent width of Brγ to other age constraints from the literature we show that the star formation must have occurred not only recently but in a short-duration burst. The current centres of star formation in all three galaxies are of a similar age but, whereas the hotspots in He 2-10 are coeval, we find phase differences between those in NGC 5253. We compare the masses and sizes of the star formation sites to those of present-day globular clusters.  相似文献   

Dynamical friction in dwarf galaxies     

X. Hernandez  & Gerard Gilmore 《Monthly notices of the Royal Astronomical Society》1998,297(2):517-525

We present a simplified analytic approach to the problem of the spiralling of a massive body orbiting within the dark halo of a dwarf galaxy. This dark halo is treated as the core region of a King distribution of dark matter particles, in consistency with the observational result of dwarf galaxies having solid-body rotation curves. Thus we derive a simple formula which provides a reliable and general first-order solution to the problem, totally analogous to the one corresponding to the dynamical friction problem in an isothermal halo. This analytic approach allows a clear handling and a transparent understanding of the physics and the scaling of the problem. A comparison with the isothermal case shows that in the core regions of a King sphere, dynamical friction proceeds at a different rate, and is sensitive to the total core radius. Thus, in principle, observable consequences may result. In order to illustrate the possible effects, we apply this formula to the spiralling of globular cluster orbits in dwarf galaxies, and show how present-day globular cluster systems could, in principle, be used to derive better limits on the structure of dark haloes around dwarf galaxies, when the observational situation improves. As a second application, we study the way a massive black hole population forming a fraction of these dark haloes would gradually concentrate towards the centre, with a consequent deformation of an originally solid-body rotation curve. This effect allows us to set limits on the fraction/mass of any massive black hole minority component of the dark haloes of dwarf galaxies. In essence, we take advantage of the way the global matter distribution fixes the local distribution function for the dark matter particles, which in turn determines the dynamical friction problem.  相似文献   

Formation and Evolution of Intermediate Mass Black Hole X-Ray Binaries     

Simon F. Portegies Zwart  Jasinta Dewi  Tom Maccarone 《Astrophysics and Space Science》2005,300(1-3):247-253

The evolution of young (≲ 10 Myr) star clusters with a density exceeding about 10⁵ star pc⁻³ are strongly affected by physical stellar collisions during their early lifetime. In such environments the same star may participate in several tens to hundreds of collisions ultimately leading to the collapse of the star to a black hole of intermediate mass. At later time, the black hole may acquire a companion star by tidal capture or by dynamical – three-body – capture. When the captured star evolves it starts to fill its Roche-lobe and transfers mass to its accompanying black hole. This then leads to a bright phase of X-ray emission, which lasts for the remaining main-sequence lifetime of the donor. If the star captured by the intermediate mass black hole is relatively low mass ≲ 2 M⊙) the binary will also be visible as a bright source in gravitational waves. Based on empirical models we argue that, for as long as the donor remains on the main sequence, the source will be ultraluminous L_x >rsim 10⁴⁰ ergs^-1 for about a week every few month. When the donor star is more massive >15 M⊙, or evolved off the main sequence the bright time is longer, but the total accretion phase lasts much shorter.  相似文献   

Spectral and photometric study of compact groups of compact galaxies     

A. S. Amirkhanian  E. Ye. Khachikian  A. G. Eghikian 《Astrophysics》2007,50(3):283-288

Results are presented from a spectral, photometric, and morphological study of two compact groups of compact galaxies (CGCG) from Shahbazian’s list. The observations were made on the 1.5-m ESO telescope and the 2.6-m telescope at the Byurakan Astrophysical Observatory (BAO) during 1999–2000. These data are compared with data for the Shahbazian compact group 4. A high spatial density of galaxies, ranging from 10000 to 100000 galaxies per Mpc³, is observed in all the groups that were studied. The discovery of a Seyfert Sy1 galaxy in the Shahbazian 355 compact group is especially noteworthy. The direct photographs of the CGCGs that were studied contain no signs of merging or tidal interactions among the members of these groups. This suggests that the galaxies in these dense systems have a common origin. __________ Translated from Astrofizika, Vol. 50, No. 3, pp. 347–353 (August 2007).  相似文献   

Outstanding Issues for Post-Main Sequence Evolution:     

Gilles Fontaine  Pierre Brassard  Stéphane Charpinet 《Astrophysics and Space Science》2003,284(1):257-268

We review the question of the empirical and theoretical instabilityregions in the HR diagram for evolved, compact stars. These include thethree families of pulsating white dwarfs (g-mode pulsators excitedthrough mechanisms associated with partial ionization and convection inthe stellar envelope), the pulsating subdwarf B stars (p-mode variablesexcited through a classic kappa mechanism associated with the radiativelevitation of iron in the stellar envelope), and the `Betsy stars',the brand new class of long-period, g-mode pulsators of the subdwarf Btype discovered recently.  相似文献