共查询到20条相似文献，搜索用时 95 毫秒
1.
Philippe Zarka Di Li Jean-Mathias Grie?meier Laurent Lamy Julien N.Girard Sbastien L.G.Hess T.Joseph W.Lazio Gregg Hallinan 《天文和天体物理学研究(英文版)》2019,(2)
We briefly review the various proposed scenarios that may lead to nonthermal radio emissions from exoplanetary systems(planetary magnetospheres, magnetosphere-ionosphere and magnetospheresatellite coupling, and star-planet interactions), and the physical information that can be drawn from their detection. The latter scenario is especially favorable to the production of radio emission above 70 MHz. We summarize the results of past and recent radio searches, and then discuss FAST characteristics and observation strategy, including synergies. We emphasize the importance of polarization measurements and a high duty-cycle for the very weak targets that radio-exoplanets prove to be. 相似文献
2.
Koijam Manihar Singh 《Astrophysics and Space Science》2010,325(1):127-135
Some new interesting solutions, the dynamics, behaviour and phenomena of rotating charged perfect fluid models are investigated,
and their physical and geometrical properties are studied in order to substantiate the possibility of the existence of such
astrophysical bodies in this Universe. The nature and role of the metric rotation Ω(r,t) as well as that of the matter rotation ω(r,t) are studied for uniform and non-uniform motions. The reactions of the gravitational and charged fields with respect to the
rotational motion are studied and possible results are explored for real astrophysical situations, and in some solutions we
find the spatial restrictions on the models for realistic conditions. Rotating models which are expanding are obtained in
which the rotational motions are decaying with time. 相似文献
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4.
Guillermo Gonzalez 《Monthly notices of the Royal Astronomical Society》1999,308(2):447-458
The chemical-dynamical properties of stars with giant planets are compared to those of a nearby star sample within the framework of a stellar orbital diffusion model. The stars-with-planets sample includes recently discovered extrasolar planets and the Sun. We find that the planet-bearing stars, 14 Her, ρ 1 Cnc and τ Boo, are much more metal-rich than stars of similar age and this cannot be easily explained by orbital diffusion. We also confirm previous claims that the motion of the Sun relative to the local standard of rest is very small compared to other G dwarfs of similar age, and we offer a possible explanation for this apparent anomaly. 相似文献
5.
Corrado Massa 《Astrophysics and Space Science》2000,271(1):83-89
We consider Einstein-like gravitational equations with Λ term proportional to the trace of the energy tensor. The possibility
of Lagrangian formulation is shortly discussed. The theory is consistent with the present-day observations, both at the local
and cosmological level. Horizon-free cosmological solutions are found and discussed. The initial condition S(0) = 0 (where S(t) is the expansion factor and t the cosmic time) requires hyperbolic space.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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7.
B. Luk 《Astronomische Nachrichten》1989,310(1):49-59
We show that the space-time of nonsingular final states of collapse is not necessarily asymptotically simple and empty (although presently favoured nuclear equations of state seem to lead to this class at least in the spherical case). The other possibility is a neutron star which can keep light on closed orbits. Wir zeigen, daß nichtsinguläre Endzustände eines Kollapses nicht notwendigerweise asymptotisch einfach und offen sind (wenngleich heute übliche nukleare Zustandsgleichungen wenigstens im sphärischen Falle zu dieser Klasse führen). Der andere Fall ist ein Neutronenstern, der Licht auf einer geschlossenen Bahn halten kann. 相似文献
8.
Arbab I. Arbab 《Astrophysics and Space Science》1996,246(2):193-196
An anisotropic model with variableG and and bulk viscosity is considered. The model exhibits an inflationary behavior during which the coefficient of bulk viscosity varies lineraly with the energy density. This allows the anisotropy energy to decrease exponentially with time. Other results overlap with our earlier work with a different ansatz for . The gravitational constant was found to increase during the radiation and matter epochs. 相似文献
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We compute velocity and the corresponding energy changes due to non-resonant interactions of protons with Alfvén solitons. It is seen that the protons heat in the perpendicular direction but associated with this is a cooling in the parallel direction.ICTP (Trieste) Fellow under programme: Training and Research in Italian Laboratories.Instituto di Fisicia dello Spazio Interplanetario CNR, via G. Galilei, CP 27, 00044 Frascati, Italy. 相似文献
12.
W. T. Thompson W. M. Neupert S. D. Jordan H. Jones R. J. Thomas B. Schmieder 《Solar physics》1993,147(1):29-46
This paper describes the results of comparing SERTS-3 images obtained in the transition region line of Heii 304 with chromospheric Hei 10830 absorption, with strong coronal lines of Mgix 368 , Fexv 284 and 417 , and Fexvi 335 and 31 , with H, with Caii 8542 , and with magnetograms in Fei 8688H. All of the images are illustrated, and the image reconstruction techniques used are described and evaluated. The high correlation of the Heii 304 and Hei 10830 images, originally found by Harvey and Sheeley (1977), is confirmed and is put on a quantitative basis. We find that the supergranulation network has greater contrast, and that filaments appear darker, in 10830 than in 304 . In active regions, the 304 line follows more closely the behavior of H and Caii 8542 than the 10830 line. 相似文献
13.
Juan Getino Pablo MartÍn JosÉ M. Farto 《Celestial Mechanics and Dynamical Astronomy》1999,74(3):153-162
In this paper, the previous nutation series corresponding to the rotation of a non‐rigid earth composed of a rigid mantle
and a liquid core obtained by Getino and Ferrándiz in 1997 are notably improved by using a high performance data fitting method.
This method can be applied to many other problems presenting a non‐linear dependence on the free parameters.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
Claudio Vidal 《Celestial Mechanics and Dynamical Astronomy》1998,71(1):15-33
We consider four bodies in space with same masses forming two binaries, each one symmetric with respect to a fixed axis and
moving under Newtonian gravitation in opposite directions about this axis. It is given a direct proof that all singularities
of this model are due to collisions, and it is proved that the singularities due to simultaneous double collisions are regularizable.
The set of equilibrium points on the total collision manifold is studied as well as the possible connections among them. We
show that the set of initial conditions on a given energy surface going to quadruple collision is a union of twenty submanifolds:
twelve of them have dimension 2 and the others have dimension 3. Similarly for ejection orbits from quadruple collision.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
15.
José Antonio Belinchón 《Astrophysics and Space Science》2002,281(4):765-775
Various models are considered with metric type flat FRW i.e. with k = 0 whose energy-momentum tensor is described by a perfect fluid whose generic equation of state is p = ωρ and taking into account the conservation principle div(T
i
j
) = 0, but considering some of the‘constants’ as variable. A set of solutions through dimensional analysis is trivially found.
The numeric calculations carried out show that the results obtained are not discordant with those presently observed for cosmological
parameters together with the electromagnetic and quantum quantities.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
Takashi Sakurai 《Solar physics》1981,69(2):343-359
A numerical method is developed for solving the force-free magnetic field equation, × B =
B, with spatially-varying . The boundary conditions required are the distribution of B
n
(viz. normal component of the field on the photosphere) as well as the value of in the region of positive (or negative) B
n
. Examples of calculations are presented for a simple model of a solar bipolar magnetic region. It is found that the field configuration and the energy stored in the field depend crucially on the distribution of . The present method can be applied to a more complex configuration observed on the Sun by making use of actual magnetic field measurements.On leave of absence from Department of Astronomy, University of Tokyo. 相似文献
17.
Yi Xie Tian-Yi Huang Department of Astronomy Nanjing University Nanjing 《中国天文和天体物理学报》2006,6(6):705-715
The dynamics of compact binaries is very complicated because of spin-orbit coupling and spin-spin coupling. With Laskar's frequency map analysis (FMA) and frequency diffusion as an indicator, we found that misalignment of the spins and orbital angular momentum has a great effect on the dynamics, and for systems with different mass ratiosβ= m2/m1 chaos occurs at different spin-orbit configurations. For equal-mass binaries (β= 1), chaos occurs when the spins nearly cancel each other out. For some other systems (for exampleβ~ 1/2), the binaries are irregular, even chaotic, when the spins are perpendicular to the orbital angular momentum. For the case where gravitational radiation is taken into account, we give an analytic estimation for the frequency diffusion based on the decay of the orbit, which is roughly consistent with our simulations. This means the FMA is not suitable as a chaos indicator for weak chaotic cases with dissipative terms. 相似文献
18.
Priscilla Sousa-Silva Maisa O. Terra Matteo Ceriotti 《Astrophysics and Space Science》2018,363(10):210
This contribution deals with fast Earth–Moon transfers with ballistic capture in the patched three-body model. We compute ensembles of preliminary solutions using a model that takes into account the relative inclination of the orbital planes of the primaries. The ballistic capture orbits around the Moon are obtained relying on the hyperbolic invariant structures associated to the collinear Lagrangian points of the Earth–Moon system, and the Sun–Earth system portion of the transfers are quasi-periodic orbits obtained by a genetic algorithm. The trajectories are designed to be good initial guesses to search optimal cost-efficient short-time Earth–Moon transfers with ballistic capture in more realistic models. 相似文献
19.
A strong coupling between convection and pulsations is known to play a major role in the disappearance of unstable modes close to the red edge of the classical Cepheid instability strip. As mean-field models of time-dependent convection rely on weakly-constrained parameters (see, e.g., Baker in Physical Processes in Comets, Stars and Active Galaxies, p. 105, 1987), we tackle this problem by the means of 2-D Direct Numerical Simulations (DNS) of the κ-mechanism with convection. Using a linear stability analysis, we first determine the physical conditions favourable for the κ-mechanism to occur inside a purely-radiative layer. Both the instability strips and the nonlinear saturation of unstable modes are then confirmed by the corresponding DNS. We next present the new simulations with convection, where a convective zone and the driving region overlap. The coupling between the convective motions and acoustic modes is then addressed by using projections onto an acoustic subspace. 相似文献
20.
Shu-Mei Jia Yong Chen Li Chen Department of Astronomy Beijing Normal University Beijing Key Laboratory of Particle Astrophysics Institute of High Energy Physics Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2006,6(2):181-196
We revisit the XMM-Newton observation of the galaxy cluster Abell 1650 with a deprojection technique. We find that the radial deprojected spectra of Abell 1650 can be marginally fitted by a single-temperature model. In order to study the properties of the central gas, we fit the spectra of the central two regions with a two-temperature model. The fits then become significantly better and the cool gas about 1-2keV can be connected with the gas cooling. Fitting the central spectrum (r ≤ 1') by using a cooling flow model with an isothermal component yields a small mass deposition rate of 10-7 11 M⊙ yr-1, while the standard cooling flow model can not fit this spectrum satisfactorily except that there exists a cut-off temperature having a level of about 3 keV. From the isothermal model we derive the deprojected electron density profile ne(r), and then together with the deprojected temperature profile the total mass and gas mass fraction of cluster are also determined. We compare the properties of Abell 1650 with those of Abell 1835 (a large cooling flow cluster) and some other clusters, to explore the difference in properties between large and small cooling flow cluster, and what causes the difference in the cooling flow of different clusters. It has been shown that Abell 1835 has a steeper potential well and thus a higher electron density and a lower temperature in its center, indicating that the shape of the gravitational potential well in central region determines the cooling flow rates of clusters. We calculate the potential, internal and radiated energies of these two clusters, and find that the gas energies in both clusters are conserved during the collapsing stage. 相似文献