A deep AAOmega survey of low-luminosity galaxies in the Shapley supercluster: stellar population trends     

Russell J. Smith  John R. Lucey  Michael J. Hudson 《Monthly notices of the Royal Astronomical Society》2007,381(3):1035-1052

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Multidimensional treatment of photon emission from accretion discs around black holes     

Kazunori Kohri  Ken Ohsuga  Ramesh Narayan 《Monthly notices of the Royal Astronomical Society》2007,381(3):1267-1274

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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   

Optical follow-up of new Small Magellanic Cloud wing Be/X-ray binaries     

M. P. E. Schurch  M. J. Coe  K. E. McGowan  V. A. McBride  D. A. H. Buckley  J. L. Galache  R. H. D. Corbet  M. Still  P. Vaisanen  A. Kniazev  K. Nordsieck 《Monthly notices of the Royal Astronomical Society》2007,381(4):1561-1568

We investigate the optical counterparts of recently discovered Be/X-ray binaries in the Small Magellanic Cloud (SMC). In total four sources, SXP101, SXP700, SXP348 and SXP65.8 were detected during the Chandra survey of the wing of the SMC. SXP700 and SXP65.8 were previously unknown. Many optical ground-based telescopes have been utilized in the optical follow-up, providing coverage in both the red and blue bands. This has led to the classification of all of the counterparts as Be stars and confirms that three lie within the Galactic spectral distribution of known Be/X-ray binaries. SXP101 lies outside this distribution and is the latest spectral type known. Monitoring of the Hα emission line suggests that all the sources barring SXP700 have highly variable circumstellar discs, possibly a result of their comparatively short orbital periods. Phase-resolved X-ray spectroscopy has also been performed on SXP65.8, revealing that the emission is indeed harder during the passage of the X-ray beam through the line of sight.  相似文献   

The response of self-gravitating protostellar discs to slow reduction in cooling time-scale: the fragmentation boundary revisited     

C. J. Clarke  E. Harper-Clark  G. Lodato 《Monthly notices of the Royal Astronomical Society》2007,381(4):1543-1547

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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   

Structure and clumping in the fast wind of NGC 6543     

R. K. Prinja  S. E. Hodges  D. L. Massa  A. W. Fullerton  A. W. Burnley 《Monthly notices of the Royal Astronomical Society》2007,382(1):299-307

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Erratum: Modelling the Galactic bar using OGLE-II red clump giant stars     

《Monthly notices of the Royal Astronomical Society》2007,382(3):1376-1376

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The space density of cataclysmic variables: constraints from the ROSAT North Ecliptic Pole survey     

M. L. Pretorius  C. Knigge  D. O'Donoghue  J. P. Henry  I. M. Gioia  C. R. Mullis 《Monthly notices of the Royal Astronomical Society》2007,382(3):1279-1288

We use the ROSAT North Ecliptic Pole (NEP) survey to construct a small, but purely X-ray flux-limited sample of cataclysmic variable stars (CVs). The sample includes only four systems, two of which (RX J1715.6+6856 and RX J1831.7+6511) are new discoveries. We present time-resolved spectroscopy of the new CVs and measure orbital periods of 1.64 ± 0.02 and 4.01 ± 0.03 h for RX J1715.6+6856 and RX J1831.7+6511, respectively. We also estimate distances for all the CVs in our sample, based mainly on their apparent brightness in the infrared. The space density of the CV population represented by our small sample is  1.1^+2.3_−0.7× 10⁻⁵ pc⁻³  . We can also place upper limits on the space density of any subpopulation of CVs too faint to be included in the NEP survey. In particular, we show that if the overall space density of CVs is as high as  2 × 10⁻⁴ pc⁻³  (as has been predicted theoretically), the vast majority of CVs must be fainter than   L _X≃ 2 × 10²⁹ erg s⁻¹  .  相似文献   

The UV properties of E+A galaxies: constraints on feedback-driven quenching of star formation     

S. Kaviraj  L. A. Kirkby  J. Silk  M. Sarzi 《Monthly notices of the Royal Astronomical Society》2007,382(3):960-970

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