The accelerated Kepler problem     

F. Namouni  M. Guzzo 《Celestial Mechanics and Dynamical Astronomy》2007,99(1):31-44

The accelerated Kepler problem (AKP) is obtained by adding a constant acceleration to the classical two-body Kepler problem. This setting models the dynamics of a jet-sustaining accretion disk and its content of forming planets as the disk loses linear momentum through the asymmetric jet-counterjet system it powers. The dynamics of the accelerated Kepler problem is analyzed using physical as well as parabolic coordinates. The latter naturally separate the problem’s Hamiltonian into two unidimensional Hamiltonians. In particular, we identify the origin of the secular resonance in the AKP and determine analytically the radius of stability boundary of initially circular orbits that are of particular interest to the problem of radial migration in binary systems as well as to the truncation of accretion disks through stellar jet acceleration.  相似文献   

Three-dimensional simulations of a starburst wind     

Jackie L. Cooper  Geoffrey V. Bicknell  Ralph S. Sutherland  Joss Bland-Hawthorn 《Astrophysics and Space Science》2007,311(1-3):99-103

In order to better understand the formation of a starburst-driven wind, we have performed a series of three-dimensional hydrodynamical simulations in an inhomogeneous interstellar medium. We present the results of these simulations, which provide new insights into the formation of the optical filaments and the origin of the soft X-ray emission.  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   

Laboratory Exploration of Solar Energetic Phenomena     

David Alexander 《Astrophysics and Space Science》2007,307(1-3):197-202

The solar atmosphere displays a wide variety of dynamic phenomena driven by the interaction of magnetic fields and plasma. In particular, plasma jets in the solar chromosphere and corona, coronal heating, solar flares and coronal mass ejections all point to the presence of magnetic phenomena such as reconnection, flux cancellation, the formation of magnetic islands, and plasmoids. While we can observe the signatures and gross features of such phenomena we cannot probe the essential physics driving them, given the spatial resolution of current instrumentation. Flexible and well-controlled laboratory experiments, scaled to solar parameters, open unique opportunities to reproduce the relevant unsteady phenomena under various simulated solar conditions. The ability to carefully control these parameters in the laboratory allows one to diagnose the dynamical processes which occur and to apply the knowledge gained to the understanding of similar processes on the Sun, in addition directing future solar observations and models. This talk introduces the solar phenomena and reviews the contributions made by laboratory experimentation.  相似文献   

Alignment and precession of a black hole with a warped accretion disc     

Rebecca G. Martin  J. E. Pringle  Christopher A. Tout 《Monthly notices of the Royal Astronomical Society》2007,381(4):1617-1624

We consider the shape of an accretion disc whose outer regions are misaligned with the spin axis of a central black hole and calculate the steady state form of the warped disc in the case where the viscosity and surface densities are power laws in the distance from the central black hole. We discuss the shape of the resulting disc in both the frame of the black hole and that of the outer disc. We note that some parts of the disc and also any companion star maybe shadowed from the central regions by the warp. We compute the torque on the black hole caused by the Lense–Thirring precession, and hence compute the alignment and precession time-scales. We generalize the case with viscosity and hence surface density independent of radius to more realistic density distributions for which the surface density is a decreasing function of radius. We find that the alignment time-scale does not change greatly but the precession time-scale is more sensitive. We also determine the effect on this time-scale if we truncate the disc. For a given truncation radius, the time-scales are less affected for more sharply falling density distributions.  相似文献   

Electromagnetic fields in jets     

B. D. Sherwin  D. Lynden-Bell 《Monthly notices of the Royal Astronomical Society》2007,378(2):409-415

The magnetic fields and energy flows in an astronomical jet described by our earlier model are calculated in detail. Though the field distribution varies with the external pressure function   p ( z )  , it depends only weakly on the other boundary conditions. Individual field lines were plotted; the lines become nearly vertical at the bottom and are twisted at the top. An animation of a field line's motion was made, which shows the line being wound up by the accretion disc's differential rotation and rising as a result of this. The distribution of Poynting flux within the jet indicates that much of the energy flows up the jet from the inside of the accretion disc but a substantial fraction flows back down to the outside.  相似文献   

A highly polarized radio jet during the 1998 outburst of the black hole transient XTE J1748–288     

C. Brocksopp  J. C. A. Miller-Jones  R. P. Fender  B. W. Stappers 《Monthly notices of the Royal Astronomical Society》2007,378(3):1111-1117

XTE J1748−288 is a black hole X-ray transient which went into outburst in 1998 June. The X-ray light curves showed canonical morphologies, with minor variations on the 'fast rise exponential decay' profile. The radio source, however, reached an unusually high flux density of over 600 mJy. This high radio flux was accompanied by an exceptional  (>20  per cent)  fractional linear polarization, the variability of which was anticorrelated with the flux density. We use this variability to discuss possible depolarization mechanisms and to predict the underlying behaviour of the (unresolved) core/jet components.  相似文献   

Superdiscs in radio galaxies: jet–wind interactions     

Gopal-Krishna    Paul J. Wiita  Santosh Joshi † 《Monthly notices of the Royal Astronomical Society》2007,380(2):703-711

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Frequency-dependent time delays for strong outbursts in selected blazars from the Metsähovi and UMRAO monitoring data bases – II     

T. B. Pyatunina  N. A. Kudryavtseva †  D. C. Gabuzda ‡  S. G. Jorstad  M. F. Aller  H. D. Aller  H. Teräsranta 《Monthly notices of the Royal Astronomical Society》2007,381(2):797-808

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The jet-powered optical nebula of Cygnus X–1     

D. M. Russell  R. P. Fender  E. Gallo †  C. R. Kaiser 《Monthly notices of the Royal Astronomical Society》2007,376(3):1341-1349

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