The efficiency of the spiral-in of a black hole to the Galactic Centre     

Piero F. Spinnato  Michael Fellhauer  Simon F. Portegies Zwart 《Monthly notices of the Royal Astronomical Society》2003,344(1):22-32

We study the efficiency at which a black hole or dense star cluster spirals in to the Galactic Centre. This process takes place on a dynamical friction time-scale, which depends on the value of the Coulomb logarithm (ln Λ). We determine the accurate value of this parameter using the direct N -body method, a tree algorithm and a particle-mesh technique with up to two million plus one particles. The three different techniques are in excellent agreement. Our measurement for the Coulomb logarithm appears to be independent of the number of particles. We conclude that  ln Λ= 6.6 ± 0.6  for a massive point particle in the inner few parsec of the Galactic bulge. For an extended object, such as a dense star cluster, ln Λ is smaller, with a value of the logarithm argument Λ inversely proportional to the object size.  相似文献   

A simple model for lensing by black holes in galactic nuclei     

M. C. Werner  N. W. Evans 《Monthly notices of the Royal Astronomical Society》2006,368(3):1362-1368

The lensing properties of the Plummer model with a central point mass and external shear are derived, including the image multiplicities, critical curves and caustics. This provides a simple model for a flattened galaxy with a central supermassive black hole. For the Plummer model with black hole, the maximum number of images is four, provided the black hole mass is less than an upper bound which is calculated analytically. This introduces a method to constrain black hole masses by counting images, thus applicable at cosmological distance. With shear, the maximum number of images is six and we illustrate the occurrence of an astroid caustic and two metamorphoses.  相似文献   

Multiple stellar populations in the Sextans dwarf spheroidal galaxy?     

M. Bellazzini  F.R. Ferraro  E. Pancino † 《Monthly notices of the Royal Astronomical Society》2001,327(1):L15-L20

We present wide-field     multiband ( BVI ) CCD photometry (down to     of the very low surface brightness dwarf spheroidal galaxy Sextans. In the derived colour–magnitude diagrams we find evidence suggesting the presence of multiple stellar populations in this dwarf spheroidal. In particular, we discover (i) a blue horizontal branch tail that appears to lie on a brighter sequence with respect to the prominent red horizontal branch and the RR Lyrae stars, very similar to what was found by Majewski et al. for the Sculptor dwarf spheroidal, (ii) hints of a bimodal distribution in colour of the red giant branch stars, (iii) a double red giant branch bump. All of these features suggest that (at least) two components are present in the old stellar population of this galaxy: the main one with     and a minor component around     . The similarity to the Sculptor case may indicate that multiple star formation episodes are also common in the most nearby dwarf spheroidals that ceased their star formation activity at very early epochs.  相似文献   

A Unified Model for Black Hole X-Ray Binary Jets?     

Rob Fender  Tomaso Belloni  Elena Gallo 《Astrophysics and Space Science》2005,300(1-3):1-13

We have recently put forward a ‘unified’ semi-empirical model for the coupling between accretion and jet production in galactic black hole X-ray binaries. In this paper, we summarise this model and briefly discuss relevant considerations that have arisen since its publication.  相似文献   

Covariant magnetoionic theory – II. Radiative transfer     

Avery Broderick  Roger Blandford 《Monthly notices of the Royal Astronomical Society》2004,349(3):994-1008

  相似文献   

X-shaped radio galaxies as observational evidence for the interaction of supermassive binary black holes and accretion disc at parsec scale     

F. K. Liu 《Monthly notices of the Royal Astronomical Society》2004,347(4):1357-1369

  相似文献   

Stellar models and Hyades: the Hipparcos test     

V. Castellani  S. Degl'Innocenti  P. G. Prada Moroni 《Monthly notices of the Royal Astronomical Society》2001,320(1):66-72

We compare theoretical stellar models for main sequence (MS) stars with the Hipparcos data base for the Hyades cluster to give a warning against the uncritical use of available theoretical scenarios and to show how formal MS fittings can be fortuitous if not fictitious. Moreover, we find that none of the current theoretical scenarios appears able to account for an observed mismatch between theoretical predictions and observations of the coolest Hyades MS stars. Finally, we show that current theoretical models probably give too faint He burning luminosities unlike the case of less massive He burning models, with degenerate progenitors, which have been suggested to suffer the opposite discrepancy.  相似文献   

Galaxy merging, the fundamental plane of elliptical galaxies and the  M_BH−σ₀  relation     

C. Nipoti  P. Londrillo  L. Ciotti 《Monthly notices of the Royal Astronomical Society》2003,342(2):501-512

  相似文献   

Black hole winds     

A. R. King  K. A. Pounds 《Monthly notices of the Royal Astronomical Society》2003,345(2):657-659

  相似文献   

Chandra and RXTE spectroscopy of the Galactic microquasar XTE J1550−564 in outburst     

J. M. Miller  H. L. Marshall  R. Wijnands †  T. Di Matteo  D. W. Fox  J. Kommers  D. Pooley  T. Belloni  J. Casares  P. A. Charles  A. C. Fabian  M. van der Klis  W. H. G. Lewin 《Monthly notices of the Royal Astronomical Society》2003,338(1):7-13

  相似文献