The radio properties of the cD galaxy of Abell 2390     

Pedro Augusto  Alastair C. Edge  Claire J. Chandler 《Monthly notices of the Royal Astronomical Society》2006,367(1):366-374

We present multifrequency, multi-epoch radio imaging of the complex radio source B2151+174 in the core of the cluster, Abell 2390  ( z ≃ 0.23)  . From new and literature data, we conclude that the Faranoff–Riley type II (FRII)-powerful radio source is the combination of a compact, core-dominated 'medium-sized symmetric object' (MSO) with a more extended, steeper spectrum mini-halo. B2151+174 is unusual in a number of important aspects. (i) It is one of the most compact and flat spectrum sources in a cluster core known; (ii) it shows a complex, compact twin-jet structure in a north–south orientation; (iii) the orientation of the jets is 45° misaligned with apparent structure (ionization cones and dust disc) of the host galaxy on larger scales. Since the twin-jet of the MSO has its northern half with an apparent 'twist', it might be that precession of the central supermassive black hole explains this misalignment. B2151+174 may be an example of the early stage (10³–10⁴ yr duration) of a 'bubble' being blown into the intracluster medium where the plasma has yet to expand.  相似文献   

Observations of the cosmic microwave background and galactic foregrounds at 12–17 GHz with the COSMOSOMAS experiment     

S. Fernández-Cerezo  C. M. Gutiérrez  R. Rebolo  R. A. Watson  R. J. Hoyland  S. R. Hildebrandt  J. A. Rubiño-Martín  J. F. Macías-Pérez  P. Sosa Molina 《Monthly notices of the Royal Astronomical Society》2006,370(1):15-24

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The star formation history of early-type galaxies as a function of mass and environment     

M. S. Clemens  A. Bressan  B. Nikolic  P. Alexander  F. Annibali  R. Rampazzo 《Monthly notices of the Royal Astronomical Society》2006,370(2):702-720

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Dissipationless collapse, weak homology and central cores of elliptical galaxies     

Carlo Nipoti  Pasquale Londrillo  Luca Ciotti 《Monthly notices of the Royal Astronomical Society》2006,370(2):681-690

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The scattered disk as a source of Halley-type comets     

Harold F. Levison  Martin J. Duncan 《Icarus》2006,184(2):619-633

We investigate a new dynamical mechanism for producing Halley-type comets from the scattered disk of comets. Levison and Duncan [Levison, H., Duncan, M., 1997. Icarus 127, 13-32] and Duncan and Levison [Duncan, M., Levison, H., 1997. Science 276, 1670-1672] showed that a significant number of objects leave the scattered disk by evolving to semi-major axes greater than 1000 AU. We find that once these objects reach semi-major axes on the order of ¹⁰⁴ AU, a significant fraction immediately have their perihelia driven inward by the galactic tides. Approximately 0.01% of the objects that reach ¹⁰⁴ AU then evolve onto orbits similar to the observed Halley-like comets due to gravitational interactions with the giant planets. The orbital element distribution resulting from this process is statistically consistent with observations. We discuss the implications of this model for the number of objects in the scattered disk in the text. The model predicts a temporal variation in the influx of HTCs with a period of ∼118 Myr. At the peak, the model predicts that there should be roughly 10 times as many HTCs as currently observed (i.e., there should be weak HTC showers). However, the model may inflate the importance of these showers because it does not include the effects of passing stars and giant molecular clouds.  相似文献   

The 2005 outburst of GRO J1655−40: spectral evolution of the rise, as observed by Swift     

C. Brocksopp  K. E. McGowan  H. Krimm  O. Godet  P. Roming  K. O. Mason  N. Gehrels  M. Still  K. Page  A. Moretti  C. R. Shrader  S. Campana  J. Kennea 《Monthly notices of the Royal Astronomical Society》2006,365(4):1203-1214

We present Swift observations of the black hole X-ray transient, GRO J1655−40, during the recent outburst. With its multiwavelength capabilities and flexible scheduling, Swift is extremely well suited for monitoring the spectral evolution of such an event. GRO J1655−40 was observed on 20 occasions and data were obtained by all instruments for the majority of epochs. X-ray spectroscopy revealed spectral shapes consistent with the 'canonical' low/hard, high/soft and very high states at various epochs. The soft X-ray source (0.3–10 keV) rose from quiescence and entered the low/hard state, when an iron emission line was detected. The soft X-ray source then softened and decayed, before beginning a slow rebrightening and then spending ∼3 weeks in the very high state. The hard X-rays (14–150 keV) behaved similarly but their peaks preceded those of the soft X-rays by up to a few days; in addition, the average hard X-ray flux remained approximately constant during the slow soft X-ray rebrightening, increasing suddenly as the source entered the very high state. These observations indicate (and confirm previous suggestions) that the low/hard state is key to improving our understanding of the outburst trigger and mechanism. The optical/ultraviolet light curve behaved very differently from that of the X-rays; this might suggest that the soft X-ray light curve is actually a composite of the two known spectral components, one gradually increasing with the optical/ultraviolet emission (accretion disc) and the other following the behaviour of the hard X-rays (jet and/or corona).  相似文献   

Long-term variations in the microwave brightness temperature of the Uranus atmosphere     

M.J. Klein 《Icarus》2006,184(1):170-180

We present a self-consistent, 36-year record of the disk-averaged radio brightness of Uranus at wavelengths near 3.5 cm. It covers nearly half a uranian year, and includes both equatorial and polar viewing geometries (corresponding to equinox and solstice, respectively). We find large (greater than 30 K) changes over this time span. In agreement with analyses made of more limited microwave data sets, our observations suggest the changes are not caused by geometric effects alone, and that temporal variations may exist in the deep uranian troposphere down to pressures of tens of bars. Our data also support an earlier suggestion that a rapid, planetary-scale change may have occurred in late 1993 and early 1994. The seasonal record presented here will be useful for constraining dynamical models of the deep atmosphere, and for interpreting observations made during Uranus' 2007 equinox passage. As part of a multi-wavelength observing campaign for this event, the Goldstone-Apple Valley Radio Telescope (GAVRT) project will continue to make frequent, single-dish observations near 3.5 cm.  相似文献   

Black hole spin in GRS 1915+105   总被引：2，自引：0，他引：2  

Matthew Middleton  Chris Done  Marek Gierli&#;ski  Shane W. Davis 《Monthly notices of the Royal Astronomical Society》2006,373(3):1004-1012

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Sérsic properties of disc galaxy mergers     

H. Aceves  H. Velázquez  F. Cruz 《Monthly notices of the Royal Astronomical Society》2006,373(2):632-642

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Studies of accretion flows around rotating black holes – II. Standing shocks in the pseudo-Kerr geometry     

Soumen Mondal  Sandip K. Chakrabarti 《Monthly notices of the Royal Astronomical Society》2006,371(3):1418-1426

Standing, propagating or oscillating shock waves are common in accretion and winds around compact objects. We study the topology of all possible solutions using the pseudo-Kerr geometry. We present the parameter space spanned by the specific energy and angular momentum and compare it with that obtained from the full general relativity to show that the potential can work satisfactorily in fluid dynamics also, provided the polytropic index is suitably modified. We then divide the parameter space depending on the nature of the solution topology. We specifically study the nature of the standing Rankine–Hugoniot shocks. We also show that as the Kerr parameter is increased, the shock location generally moves closer to the black hole. In future, these solutions can be used as guidelines to test numerical simulations around compact objects.  相似文献