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C. Íbanoğlu E.R. Pekünlü V. KESKÍn Z. Tunca S. Evren M.C. Akan 《Astrophysics and Space Science》1997,257(1):11-21
The peculiar chromospherically active binary system RT Lac was observed in B and V bands between 1989 and 1992. The four-year photoelectric B and V light curves are presented. The light and colour variations in the four special regions of the light curve between 1978 and 1992 are discussed. The available photometry obtained by the present authors defines at least three consecutive maxima in the variation of the brightness of the system at second maximum and in mid-primary eclipse. The behaviour of the light and colour changes in mid-primary and at second maximum harmonizes with the common property of the RS CVn-type binaries. However, the light changes at first maximum do not resemble either at second maximum or in mid-primary minimum. Therefore, we conclude that the observed features cannot be attributed to the spottedness of the more massive component alone. The signs of the starspots are masked by the matter in front of the more massive component at the first maximum. The present data indicate that the magnetic cycle in RT Lac is about 12 years, which is analogous to the Sun's 11-year sunspot cycle. 相似文献
826.
Large-scale, decelerating, relativistic X-ray jets from microquasar XTE J1550−564 has been recently discovered with Chandra by Corbel et al. (2002). We find that the dynamical evolution of the approaching jet at the late time is consistent with
the well-known Sedov evolutionary phase R∝ t
2/5. A trans-relativistic external shock dynamic model by analogy with the evolution of gamma-ray burst remnants, is shown to
be able to fit the proper-motion data of the approaching jet reasonably well. The inferred interstellar medium density around
the source is well below the canonical value n
ISM∼1 cm−3. The rapidly fading X-ray emission can be interpreted as synchrotron radiation from the non-thermal electrons in the adiabatically
expanding ejecta. These electrons were accelerated by the reverse shock (moving back into the ejecta) which becomes important
when the inertia of the swept external matter leads to an appreciable slowing down of the original ejecta. 相似文献
827.
Contribution to diffuse gamma-rays in the Galactic Centre region from unresolved millisecond pulsars
W. Wang Z. J. Jiang K. S. Cheng 《Monthly notices of the Royal Astronomical Society》2005,358(1):263-269
Diffuse gamma-rays in the Galactic Centre region have been studied. We propose that there exists a population of millisecond pulsars in the Galactic Centre, which emit GeV gamma-rays through synchrotron-curvature radiation as predicted by outer gap models. These GeV gamma-rays from unresolved millisecond pulsars probably contribute to the diffuse gamma-ray spectrum detected by EGRET which displays a break at a few GeV. We have used a Monte Carlo method to obtain simulated samples of millisecond pulsars in the Galactic Centre region covered by EGRET (∼ 15) according to the different period and magnetic field distributions from observed millisecond pulsars in the Galactic field and globular clusters, and superposed their synchrotron-curvature spectra to derive the total GeV flux. Our simulated results suggest that there probably exist about 6000 unresolved millisecond pulsars in the region of angular resolution of EGRET, the emissions of which could contribute significantly to the observed diffuse gamma-rays in the Galactic Centre. 相似文献
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Based on the stochastic and phenomenological aspects of hydrological processes, a conceptually based stochastic point process (SPP) model for daily stream‐flow generation is proposed in this paper. In which, storms are defined by a stochastic point process with marked values. All the random variables defining the process are assumed to be mutually independent, which constitutes a compound Poisson point process. The direct surface runoff is regarded as occurring from storage in a cascade of surface linear reservoirs and is responsible for the short‐term variation of the daily stream flows. The baseflow component is considered as coming from subsurface/groundwater storage and is responsible for the long‐term persistence of the storm time‐series. This type of model is proposed as a more realistic model of daily stream flow than models based on pure stochastic processes. Studies on the instantaneous unit hydrograph and the mechanism of baseflow could thereby provide some parameters for this model. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
830.
Mapping of Io's thermal radiation by the Galileo photopolarimeter-radiometer (PPR) instrument 总被引:1,自引:0,他引:1
Between 1999 and 2002, the Galileo spacecraft made 6 close flybys of Io during which many observations of Io's thermal radiation were made with the photopolarimeter-radiometer (PPR). While the NIMS instrument could measure thermal emission from hot spots with T>200 K, PPR was the only Galileo instrument capable of mapping the lower temperatures of older, cooling lava flows, and the passive background. We tabulate all data taken by PPR of Io during these flybys and describe some scientific highlights revealed by the data. The data include almost complete coverage of Io at better than 250 km resolution, with extensive regional coverage at higher resolutions. We found a modest poleward drop in nighttime background temperatures and evidence of thermal inertia variations across the surface. Comparison of high spatial resolution temperature measurements with observed daytime SO2 gas pressures on Io provides evidence for local cold trapping of SO2 frost on scales smaller than the 60 km resolution of the PPR data. We also calculated the power output from several hot spots and estimated total global heat flow to be about 2.0-2.6 W m−2. The low-latitude diurnal temperature variations for the regions between obvious hot spots are well matched by a laterally-inhomogeneous thermal model with less than 1 W m−2 endogenic heat flow. 相似文献