The size distribution of trans-Neptunian bodies     

J.R. Donnison 《Planetary and Space Science》2006,54(3):243-250

The magnitude distribution of the trans-Neptunian bodies composed of the Kuiper Belt Objects (KBOs) and Scattered Disk Objects (SDOs) is determined for absolute magnitudes H?7, using maximum likelihood estimation methods. This is translated into a corresponding size distribution. This gave a differential size index of q=3.966±0.15 for KBOs and q=3.016±0.32 for SDOs. It was found that these two distributions were statistically different. The KBOs were further split into classical KBOs and Plutinos which had indices of q=4.074±0.18 and q=3.301±0.37, respectively. There was no statistical evidence that these are different populations. The classical KBOs were further split and examined for four different semi-major axis ranges and it was found that there was moderate evidence that the entire sample was not well represented by one index. The distribution indices of the SDOs were compared with the distributions of short period comets and found to be similar. It is likely that the scattered disk population is the source of the short period comets.  相似文献   

Opening angles, Lorentz factors and confinement of X-ray binary jets     

J. C. A. Miller-Jones  R. P. Fender  E. Nakar 《Monthly notices of the Royal Astronomical Society》2006,367(4):1432-1440

We present a collation of the available data on the opening angles of jets in X-ray binaries, which in most cases are small (≲10°). Under the assumption of no confinement, we calculate the Lorentz factors required to produce such small opening angles via the transverse relativistic Doppler effect. The derived Lorentz factors, which are in most cases lower limits, are found to be large, with a mean >10, comparable to those estimated for active galactic nuclei (AGN) and much higher than the commonly assumed values for X-ray binaries of 2–5. Jet power constraints do not, in most cases, rule out such high Lorentz factors. The upper limits on the opening angles show no evidence for smaller Lorentz factors in the steady jets of Cygnus X-1 and GRS 1915+105. In those sources in which deceleration has been observed (notably  XTE J1550−564  and Cygnus X-3), some confinement of the jets must be occurring, and we briefly discuss possible confinement mechanisms. It is however possible that all the jets could be confined, in which case the requirement for high bulk Lorentz factors can be relaxed.  相似文献   

Photoevaporation of protoplanetary discs – I. Hydrodynamic models     

R. D. Alexander  C. J. Clarke  J. E. Pringle 《Monthly notices of the Royal Astronomical Society》2006,369(1):216-228

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Unification scheme and the distribution of neutral gas in compact radio sources     

Neeraj Gupta  D. J. Saikia 《Monthly notices of the Royal Astronomical Society》2006,370(2):738-742

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Effect of signal contamination in matched-filter detection of the signal on a cluttered background     

Theiler  J. Foy  B.R. 《Geoscience and Remote Sensing Letters, IEEE》2006,3(1):98-102

To derive a matched filter for detecting a weak target signal in a hyperspectral image, an estimate of the band-to-band covariance of the target-free background scene is required. We investigate the effects of including some of the target signal in the background scene. Although the covariance is contaminated by the presence of a target signal (there is increased variance in the direction of the target signature), we find that the matched filter is not necessarily affected. In fact, if the variation in plume strength is strictly uncorrelated with the variation in background spectra, the matched filter and its signal-to-clutter ratio (SCR) performance will not be impaired. While there is little a priori reason to expect significant correlation between the plume and the background, there usually is some residual correlation, and this correlation leads to a suppressing effect that limits the SCR obtainable even for strong plumes. These effects are described and quantified analytically, and the crucial role of this correlation is illustrated with some numerical examples using simulated plumes superimposed on real hyperspectral imagery. In one example, we observe an order-of-magnitude loss in SCR for a matched filter based on the contaminated covariance.  相似文献   

The 2dF QSO Redshift Survey – XII. The spectroscopic catalogue and luminosity function     

S. M. Croom  R. J. Smith  B. J. Boyle  T. Shanks  L. Miller  P. J. Outram  N. S. Loaring 《Monthly notices of the Royal Astronomical Society》2004,349(4):1397-1418

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High-resolution observations of a complete sample of 27 FR II radio galaxies and quasars with 0.3 < z < 0.6     

G. M. Gilbert  J. M. Riley  M. J. Hardcastle  J. H. Croston  G. G. Pooley  P. Alexander 《Monthly notices of the Royal Astronomical Society》2004,351(3):845-890

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Erratum: Towards cosmological concordance on galactic scales     

Frank C. van den Bosch  H. J. Mo  Xiaohu Yang 《Monthly notices of the Royal Astronomical Society》2004,348(2):736-736

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On The Concept Of Periapsis In Hill’s Problem     

B.F. Villac  D.J. Scheeres 《Celestial Mechanics and Dynamical Astronomy》2004,90(1-2):165-178

The concept of closest approach is analyzed in Hill’s problem, resulting in a partitioning of the position space. The different behavior between the direct and retrograde motion is explained analytically, resulting in a simple estimate of the variation of Hill’s periodic and quasi-circular orbits as a function of the Jacobi constant. The local behavior of the orbits on the zero velocity surfaces and an analytical definition of local escape and capture in Hill’s problem are also given.  相似文献   

Optical monitoring of the quasar 4C 38.41     

B. Peng  J. Wu  X. Zhou 《Monthly notices of the Royal Astronomical Society》2003,346(2):483-488

The results of a photometric monitoring of the quasar 4C 38.41, performed at the optical R and B bands in 2002 February–March, are presented. With a 60/90 cm Schmidt telescope at the Xinglong station of the National Astronomical Observatories of China, we observed the source exhibiting amplitude variations of up to 0.78 mag in both bands during the whole campaign. Intraday and even intranight variations are detected as well. A typical variability time-scale of about 36 d is derived from our 2-month observations at the optical bands, which is identical to that found at a radio wavelength of 92 cm, suggesting a common origin for the variations in 4C 38.41 from optical to radio bands.  相似文献