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991.
The orbital period variation of the oEA system Y Leo is revised by taking into account new times of minimum light covering
an extended time base of 101.8 yr. A multiperiodic ephemeris was finally established by carefully approaching the problem of periodicity detection for the considered periodic
components. A method relying on Monte Carlo simulations was applied. The problem of the long-term behaviour of the O–C curve was taken into account using parabolic, and parabolic + periodic ephemerides. The physical interpretation of the mathematical models describing both long- and short-term behaviour of the
O–C curve was performed by considering different mechanisms: the conservative mass transfer, the light-time effect, and the orbital
period modulation through the cyclic magnetic activity of the late spectral type secondary component in the system. The consequences
of these interpretations are rather intriguing and emphasize the need of new and detailed observational studies on Y Leo. 相似文献
992.
K. A. Firoz J. Hwang I. Dorotovič T. Pintér Subhash C. Kaushik 《Astrophysics and Space Science》2011,331(2):469-484
Cosmic rays registered by Neutron Monitor on the surface of the Earth are believed to originate from outer space, and sometimes
also from the exotic objects of the Sun. Whilst the intensities of the cosmic rays are observed to be enhanced with sudden,
sharp and short-lived increases, they are termed as ground level enhancements (GLEs). They are the occurrences in solar cosmic
ray intensity variations on short-term basis, so different solar factors erupted from the Sun can be responsible for causing
them. In this context, an attempt has been made to determine quantitative relationships of the GLEs having peak increase >5%
with simultaneous solar, interplanetary and geophysical factors from 1997 through 2006, thereby searching the responsible
factors which seem to cause the enhancements. Results suggest that GLE peaks might be caused by solar energetic particle fluxes
and solar flares. The proton fluxes which seemed to cause GLE peaks were also supported by their corresponding fluences. For
most of the flares, the time integrated rising portion of the flare emission refers to the strong portion of X-ray fluxes
which might be the concern to GLE peak. On an average, GLE peak associated X-ray flux (0.71×10−4 w/m2) is much stronger than GLE background associated X-ray flux (0.11×10−6 w/m2). It gives a general consent that the GLE peak is presumably caused by the solar flare. Coronal mass ejection alone does
not seem to cause GLE. Coronal mass ejection presumably causes geomagnetic disturbances characterized by geomagnetic indices
and polarities of interplanetary magnetic fields. 相似文献
993.
Xian-Feng Zhao 《Astrophysics and Space Science》2011,332(1):139-144
The effect of the Σ-meson well depth on the gravitational redshift is examined within the framework of relativistic mean field
theory for the baryon octet system. It is found that, for a stable neutron star, the gravitational redshift increases with
the central energy density increase or with the mass increase but decreases as the radius increases. Considering a change
of US(N)U_{\Sigma}^{(N)} from −30 MeV to 30 MeV, for a stable neutron star the gravitational redshift near to the maximum mass increases. In addition,
it is also found that the growth of the US(N)U_{\Sigma}^{(N)} makes the gravitational redshift as a function of M
max /R increase, the higher the US(N)U_{\Sigma}^{(N)} the less the change in the gravitational redshift. 相似文献
994.
We explore the hard X-ray source distributions of an C1.1 flare occurred on 14 December 2007. Both Hinode/EIS and RHESSI observations are used. One of EIS rasters perfectly covers the double hard X-ray footpoints, where the EUV
emission appears strong from the cool line of He ii (log T=4.7) to the hot line of Fe xvi (log T=6.4). We analyze RHESSI X-ray images at different energies and different times before the hard X-ray maximum. The results
show a similar topology for the time-dependent source distribution (i.e. at 14:14:35 UT) as that for energy-dependent source distribution (i.e. at a given energy band of 6 – 9 keV) overlapped on EUV bright kernels, which seems to be consistent with the evaporation
model. 相似文献
995.
Similarity model of feed support system for FAST 总被引:1,自引:0,他引:1
A new design of feed support system for Five hundred meter Aperture Spherical Telescope (FAST) is proposed in this paper.
According to the similarity theory, a 1:15 scale model of feed support system has been built to make systemic research on
the feasibility of the system. Then the control system and hardware structure of the feed support system are illustrated.
A complete astronomical observation track is run by the scale model and the experiments results demonstrate that the new feed
support system can satisfy the observation accuracy requirement of FAST. 相似文献
996.
Solar flares occur due to the sudden release of energy stored in active-region magnetic fields. To date, the precursors to
flaring are still not fully understood, although there is evidence that flaring is related to changes in the topology or complexity
of an active-region’s magnetic field. Here, the evolution of the magnetic field in active region NOAA 10953 was examined using
Hinode/SOT-SP data over a period of 12 hours leading up to and after a GOES B1.0 flare. A number of magnetic-field properties and
low-order aspects of magnetic-field topology were extracted from two flux regions that exhibited increased Ca ii H emission during the flare. Pre-flare increases in vertical field strength, vertical current density, and inclination angle
of ≈ 8° toward the vertical were observed in flux elements surrounding the primary sunspot. The vertical field strength and
current density subsequently decreased in the post-flare state, with the inclination becoming more horizontal by ≈ 7°. This
behavior of the field vector may provide a physical basis for future flare-forecasting efforts. 相似文献
997.
Vladimír Skalský 《Astrophysics and Space Science》2010,330(2):373-398
Assuming that the relativistic universe is homogeneous and isotropic, we can unambiguously determine its model and physical properties, which correspond with the Einstein general theory of relativity (and with its two special partial solutions: Einstein special theory of relativity and Newton gravitation theory), quantum mechanics, and observations, too. 相似文献
998.
This is a crucial time in the history of astronomy with major all-sky surveying work being carried out in all spectral bands, as well as in astrometry. The results of this activity are advancing all fields of astrophysical research, from the investigation of exo-planetary systems to the study of the chemical evolution of the Universe. Full sky surveys are available from the radio domain to X-ray wavelengths but not in the ultraviolet range (UV). While large UV missions are currently under discussion within the astrophysical community and at the major Space Agencies, the efficient use of resources requires preparatory work that can fill the UV surveying gap. This article summarizes the research and on-going activities in this field. 相似文献
999.
Studying relativistic compact objects is important in modern astrophysics to understand several astrophysical issues. It is therefore natural to ask for an internal structure and physical properties of specific classes of compact stars from astrophysical observations. We obtain a class of new relativistic solutions with anisotropic distribution of matter for compact stars. More specifically, stellar models, described by an anisotropic fluid, establishing a relation between metric potentials and generating a specific form of mass function, are explicitly constructed within the framework of General Relativity. New solutions can be used to model compact objects, which adequately describe compact strange star candidates like SMC X-1, Her X-1 and 4U 1538-52, with observational data taken from Gangopadhyay et al. (Mon. Not. R. Astron. Soc. 431:3216, 2013). As a possible astrophysical application the obtained solutions could explain the physics of selfgravitating objects, and might be useful for strong-field regimes where data are currently inadequate. 相似文献
1000.
Mingyu Wu Quanming Lu Martin Volwerk Rumi Nakamura Tielong Zhang 《Astrophysics and Space Science》2018,363(2):22
In this paper, with the in-situ observations from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes we report a wavy dipolarization front (DF) event, where the DF has different magnetic structures and electron distributions at different \(y\) positions in the Geocentric Solar Magnetospheric (GSM) coordinates. At \(y \sim2.1R_{E}\) (\(R_{E}\) is the radius of Earth), the DF has a relatively simple structure, which is similar to that of a conventional DF. At \(y \sim3.0R_{E}\), the DF is revealed to have a multiple DF structure, where the plasma exhibits a vortex flow. Such a wavy DF could be the results of the interchange instability. The different structure of such a wavy DF at different sites has a great effect on electron acceleration. Fermi acceleration can occur at the site of the DF with a simple or multiple DF structure, while betatron acceleration as a local process has the contribution to energetic electrons only at the site of the DF with a simple structure. 相似文献