Satellites of simulated galaxies: survival, merging and their relationto the dark and stellar haloes     

Laura V. Sales  Julio F. Navarro †  Mario G. Abadi  Matthias Steinmetz 《Monthly notices of the Royal Astronomical Society》2007,379(4):1464-1474

  相似文献   

Research on formation density MWD instrument in engineering geological exploration     

Dajun ZHAO  Guosheng JIANG  Youhong SUN  Junhua ZHENG  Zhuwen WANG 《世界地质(英文版)》2008,11(4)

A high efficiency method is very important in geological survey for a new city in China. Geophysical parameters are Measured While Drilling(MWD), and these parameters are processed and explained on the ground, so the method can replace conventional engineering geological exploration for drilling rock sample. According petroleum engineering MWD, using the different characters of different rock absorbs γ radial, with the method of storing data in hole and explaining data on the ground, engineering geological exploration formation density MWD is researched. The MWD works stabilized, and the performance is good with precise data.  相似文献   

2005/2006年度莱州湾东部的海冰灾害及其影响   总被引：1，自引：0，他引：1  

张绪良  谷东起  陈东景 《海洋湖沼通报》2009,(2)

莱州湾是水深较浅的半封闭海湾,与外海海水的交换缓慢,受黄河等十几条入海河流汇入的淡水影响使海水的盐度较低.受寒潮影响莱州湾内海冰灾害发生频繁.莱州湾的海冰灾害分5个冰情等级.在冬季气温偏高的年份,莱州湾内形成Ⅰ、Ⅱ级海冰,沿岸一般没有固定冰形成;一般年份形成Ⅲ级海冰,西岸和南岸冰情较严重,有固定冰形成;在冬季气温偏低的年份,形成Ⅳ级或Ⅴ级海冰,南岸、西岸的固定冰宽度较大,有时整个莱州湾海面都分布流冰.2005年末～2006年初在莱州湾东岸形成了一次较严重的海冰灾害,莱州市近海海湾扇贝养殖的经济损失达400万元以上.为减轻未来海冰灾害带来的损失提出了加强海冰灾害的监测和预报技术研究,严格管理近海养殖生产作业,莱州湾沿岸地方政府应制定<海冰灾害应急预案>,建设和完善海冰灾害应急防御体系等防御海冰灾害的对策.  相似文献   

Self-regulated gravitational accretion in protostellar discs     

E. I. Vorobyov  Shantanu Basu 《Monthly notices of the Royal Astronomical Society》2007,381(3):1009-1017

We present a numerical model for the evolution of a protostellar disc that has formed self-consistently from the collapse of a molecular cloud core. The global evolution of the disc is followed for several million years after its formation. The capture of a wide range of spatial and temporal scales is made possible by use of the thin-disc approximation. We focus on the role of gravitational torques in transporting mass inward and angular momentum outward during different evolutionary phases of a protostellar disc with disc-to-star mass ratio of order 0.1. In the early phase, when the infall of matter from the surrounding envelope is substantial, mass is transported inward by the gravitational torques from spiral arms that are a manifestation of the envelope-induced gravitational instability in the disc. In the late phase, when the gas reservoir of the envelope is depleted, the distinct spiral structure is replaced by ongoing irregular non-axisymmetric density perturbations. The amplitude of these density perturbations decreases with time, though this process is moderated by swing amplification aided by the existence of the disc's sharp outer edge. Our global modelling of the protostellar disc reveals that there is typically a residual non-zero gravitational torque from these density perturbations, i.e. their effects do not exactly cancel out in each region. In particular, the net gravitational torque in the inner disc tends to be negative during first several million years of the evolution, while the outer disc has a net positive gravitational torque. Our global model of a self-consistently formed disc shows that it is also self-regulated in the late phase, so that it is near the Toomre stability limit, with a near-uniform Toomre parameter Q ≈ 1.5–2.0. Since the disc also has near-Keplerian rotation, and comparatively weak temperature variation, it maintains a near-power-law surface density profile proportional to r ^−3/2.  相似文献   

The effect of magnetic fields on the formation of circumstellar discs around young stars     

Daniel J. Price  Matthew R. Bate 《Astrophysics and Space Science》2007,311(1-3):75-80

We present first results of our simulations of magnetic fields in the formation of single and binary stars using a recently developed method for incorporating Magnetohydrodynamics (MHD) into the Smoothed Particle Hydrodynamics (SPH) method. An overview of the method is presented before discussing the effect of magnetic fields on the formation of circumstellar discs around young stars. We find that the presence of magnetic fields during the disc formation process can lead to significantly smaller and less massive discs which are much less prone to gravitational instability. Similarly in the case of binary star formation we find that magnetic fields, overall, suppress fragmentation. However these effects are found to be largely driven by magnetic pressure. The relative importance of magnetic tension is dependent on the orientation of the field with respect to the rotation axis, but can, with the right orientation, lead to a dilution of the magnetic pressure-driven suppression of fragmentation.  相似文献   

On the origin of the kinematical differences between the stellar halo and the old globular cluster system in the Large Magellanic Cloud     

Kenji Bekki 《Monthly notices of the Royal Astronomical Society》2007,380(4):1669-1677

  相似文献   

The properties and evolution of a K-band selected sample of massive galaxies at z∼ 0.4–2 in the Palomar/DEEP2 survey     

C. J. Conselice †  K. Bundy †  I. Trujillo  A. Coil ‡  P. Eisenhardt  R. S. Ellis  A. Georgakakis  J. Huang  J. Lotz  K. Nandra  J. Newman  C. Papovich §  B. Weiner  C. Willmer 《Monthly notices of the Royal Astronomical Society》2007,381(3):962-986

  相似文献   

Active galactic nuclei and galaxy interactions   总被引：1，自引：0，他引：1  

M. Sol Alonso  Diego G. Lambas  Patricia Tissera  Georgina Coldwell 《Monthly notices of the Royal Astronomical Society》2007,375(3):1017-1024

  相似文献   

Herbig-Haro objects—tracers of the formation of low-mass stars and sub-stellar objects     

Bringfried Stecklum  Helmut Meusinger  Dirk Froebrich 《Astrophysics and Space Science》2007,311(1-3):63-67

Herbig-Haro objects (HHOs) are caused by outflows from young objects. Since the outflow relies on mass accretion from a circumstellar disk, it indicates ongoing growth. Recent results of infrared observations yielded evidence for disks around brown dwarfs. This suggests that at least a certain fraction of brown dwarfs forms like stars. Thus, young sub-stellar objects might cause HHOs as well. We present selected results of a general survey for HHOs based on DSS-II plates and CCD images taken with the Tautenburg Schmidt telescope. Numerous young objects could be identified due to their association with newly detected HHOs. In some cases the luminosity is consistent with very low-mass stars or close to sub-stellar values. This holds for L1415-IRS and a few infrared sources embedded in other dark clouds (e.g., GF9, BHR111). The question on the minimum mass for outflow activity is addressed.  相似文献   

Near-infrared and optical emission-line structure of the Keyhole Nebula in NGC 3372     

NathanSmith † 《Monthly notices of the Royal Astronomical Society》2002,331(1):7-12

Narrow-band infrared and optical images of the Keyhole Nebula in NGC 3372 reveal which structures are caused by extinction, and show the underlying morphology of photoionized and shock-excited gas. Dark clouds conspire with ionized gas to create the apparent keyhole shape, which is prominent at blue wavelengths and less apparent in the infrared. The  Pa β /H α   line ratio shows the spatial distribution of foreground extinction. The wavelength dependence of this extinction indicates a reddening law with   R ≈4.8  , different from the normal interstellar medium. This confirms previous estimates of reddening toward the Carina Nebula determined from stellar photometry, and reveals that the anomalous extinction is patchy and within the H  ii region. The morphology of the ionized gas is different from the extinction clouds; it shows an edge-on ionization front running NE to SW, with a limb-brightened indentation that forms the upper outline of the keyhole shape. A fast polar wind from η Carinae may have punctured the ionization front, since the indentation is directly along a projection of the polar axis of the star. This is supported by the morphology of shock-excited gas revealed by a high  [S  ii ]/H α   ratio. High-excitation gas emitting [O  iii ] and He  i has a smoother distribution. Molecular clumps in the region are also discussed.  相似文献