共查询到20条相似文献，搜索用时 750 毫秒
1.
We derive accurate analytic approximations to the solution of the isothermal Lane–Emden equation, a basic equation in Astrophysics that describes the Newtonian equilibrium structure of self-gravitating, isothermal fluid spheres. The solutions we obtain, using analytic arguments and rational approximations, have simple forms, and are accurate over a radial extent that is much larger than that covered by conventional series expansions around the origin. Our best approximation has a maximum error on density of 0.04 % at 10 core radii, and is still within 1 % from an accurate numerical solution at a radius three times larger. 相似文献
2.
The general relativistic Binet’s orbit equation is exactly solved using the exp-function method, two exact solutions are obtained
which are useful for theoretical analysis. 相似文献
3.
Jeremy J. Davis Daniele Mortari Christian Bruccoleri 《Celestial Mechanics and Dynamical Astronomy》2010,108(1):59-72
Seven sequential starter values for solving Kepler’s equation are proposed for fast orbit propagation. The proposed methods
have constant complexity (not iterative), do not require pre-computed data, and can be implemented in just a few lines of
code. The resulting sequential orbit propagation techniques can be done at different levels of accuracy and speed, depending
essentially on the value of orbit eccentricity. Accuracy and algorithmic complexity are evaluated for all the proposed approaches
and compared with several existing single-point techniques to solve Kepler’s equation. The new methods obtain improved accuracy
at lower computational cost as compared to the best existing methods. 相似文献
4.
5.
The Wheeler-DeWitt equation in Vilenkin model is solved via the ansatz approach when all terms related to vacuum, domain walls, strings, dust, relativistic matter, bosons and fermions and ultra stiff matter are present. 相似文献
6.
Robert A. Van Gorder 《New Astronomy》2011,16(2):65-67
Perturbation solutions are obtained for the Lane–Emden equation of the second kind which describe Bonnor–Ebert gas spheres. In particular, we employ the field-theoretic perturbative procedure due to Bender et al. to obtain analytical solutions to the nonlinear initial value problem. We find that the method allows one to construct perturbation solutions which converge rapidly to the true solutions in many cases, as it allows one to more accurately represent the influence of nonlinear terms in the linearized equations. The rapid convergence of the method results in qualitatively accurate solutions in relatively few iterations. 相似文献
7.
Wolfgang J. Duschl 《天文研究与技术》2003,(Z1)
1 IntroductionDuringthelasttwodecadesdynamicalstudiesofthenucleiofgalaxiesinthelocalUniversehaveleadtotheconclusionthatsuper massiveblackholesofsome 1 0 6 ...9M⊙arecommonlypresent(Kormendy 2 0 0 1 ,andreferencestherein) .Actually,nofirmcounterexamplehasbeenfoundyet.Soonafteritsdiscovery,thequasarphenomenonwasattributedtoaccretionontosuper massiveblackholes.Accretionratesof 1 0 - 1...+1M⊙ a- 1andblackholemassesoftypically 1 0 8...11M⊙(Lynden Bell1 969)wereinferred .Inthiscontribution ,w… 相似文献
8.
M.H. Hart (1975, Quart. J. Roy. Astron. Soc.16, 128–135) has argued that the absence of evidence for extraterrestrial visits to Earth indicates that there are no other advanced civilizations in our galaxy capable of interstellar colonization. If so, the possible success of any SETI program must be questioned. The authors propose that limited interstellar colonization may occur and an attempt is made to show the effects of such a journey on the Drake equation. 相似文献
9.
Gang-Wei Wang Tian-Zhou Xu Stephen Johnson Anjan Biswas 《Astrophysics and Space Science》2014,349(1):317-327
In this paper, complete geometric symmetry of extended quantum Zakharov–Kuznetsov (QZK) equation are investigated. All of the geometric vector fields for the new extended QZK equation are presented. At the same time, a plethora of exact solutions are obtained by the application of the group theorem. In addition, 1-soliton solution of the extended QZK equation with power law nonlinearity is obtained by the aid of traveling wave hypothesis with the necessary constraints in place for the existence of the soliton. 相似文献
10.
11.
The infinite medium Green’s function is used to solve the half-space albedo, slab albedo and Milne problems for the unpolarized Rayleigh scattering case; these problems are the most classical problems of radiative transfer theory. The numerical results are obtained and are compared with previous ones. 相似文献
12.
Cdric Foellmi 《New Astronomy》2009,14(8):674-691
We examine the distance of the two galactic microquasars GRO J1655–40 and A 0620–00 which are potentially the two closest black holes to the Sun. We aim to provide a picture as wide and complete as possible of the problem of measuring the distance of microquasars in our Galaxy. The purpose of this work is to fairly and critically review in great detail every distance method used for these two microquasars in order to show that the distances of probably all microquasars in our Galaxy are much more uncertain than currently admitted. Moreover, we show that many confirmations of quantitative results are often entangled and rely on very uncertain measurements. We also present a new determination of the maximum distance of GRO J1655–40 using red clump giant stars, and show that it confirms our earlier result of a distance less than 2 kpc instead of 3.2 kpc. Because, it then becomes more likely that GRO J1655–40 could originate from the stellar cluster NGC 6242, located at 1.0 kpc, we review the distance estimations of A 0620–00, which is so far the closest black hole with an average distance of about 1.0 kpc. We show that the distance methods used for A 0620–00 are also problematic. Finally, we present a new analysis of spectroscopic and astrometric archival data on this microquasar, and apply the maximum distance method of Foellmi et al. [Foellmi, C., Depagne, E., Dall, T.H., Mirabel, I.F., 2006b. A&A 457, 249]. It appears that A 0620–00 could indeed be even closer to the Sun than currently estimated, and consequently would be the closest known black hole to the Sun. 相似文献
13.
De Yu Wang Guang Li Huang C. -G. Fälthammar P. A. Lindqvist L. Blomberg Li Ting Song 《Astrophysics and Space Science》1996,240(2):175-186
Nonlinear kinetic Alfvén waves where m
e
/m
i
, have been solved both with and without the Poisson equation correction. It is found that the ratio of the perpendicular electric field and magnetic field, and the ratio of parallel and perpendicular electric field increase with deepening of the depressive density soliton. The former ratio may be larger than the Alfvén velocity in the case of a large amplitude solitary kinetic Alfvén wave. The Poisson equation correction is important for the nonlinear kinetic Alfvén wave propagating along the magnetic field, which solves a puzzle of Sagdeev potential to approach infinity in the limit ofK
x
0. This correction causes the solitary KAW possessing an electrostatic character along the direction of wave moving frame. These results have been compared with the observations from the Freja satellite in the low aurora. 相似文献
14.
Recently, a field theoretic model for a UV complete theory of gravity has been proposed by Hor̃ava. This theory is a non-relativistic
renormalizable gravity theory which coincides with Einstein’s general relativity at large distances. Subsequently Lü et al.
have formulated the modified Friedmann equations and have presented a solution in vacuum. In the present work, we rewrite
the modified FRW equations in the form of usual FRW equations in Einstein gravity and consequences have been analyzed. Also
the thermodynamics of the FRW universe has been studied. 相似文献
15.
S. A. Elwakil A. M. El-hanbaly E. K. El-Shewy I. S. El-Kamash 《Astrophysics and Space Science》2014,349(1):197-203
The nonlinear properties of small amplitude electron-acoustic solitary waves (EAWs) in a homogeneous system of unmagnetized collisionless plasma consisted of a cold electron fluid and isothermal ions with two different temperatures obeying Boltzmann type distributions have been investigated. A reductive perturbation method was employed to obtain the Kadomstev-Petviashvili (KP) equation. At the critical ion density, the KP equation is not appropriate for describing the system. Hence, a new set of stretched coordinates is considered to derive the modified KP equation. Moreover, the solitary solution, soliton energy and the associated electric field at the critical ion density were computed. The present investigation can be of relevance to the electrostatic solitary structures observed in various space plasma environments, such as Earth’s magnetotail region. 相似文献
16.
Priyamvada Natarajan Omar Almaini 《Monthly notices of the Royal Astronomical Society》2000,318(3):L21-L24
We use simple energetic arguments to estimate the contribution of massive X-ray binaries and supernova remnants to the cosmic X-ray background (XRB) at energies in excess of 2 keV. Recent surveys have shown that active galactic nuclei (AGN) probably account for most of the hard XRB ( E >2 keV), but there have been many suggestions that star-forming galaxies could emerge at fainter fluxes and perhaps account for a significant fraction of the soft and hard X-ray energy density. Assuming that the formation rate of massive X-ray binaries (MXRBs) traces the global star-formation rate, we find that their integrated contribution to the hard XRB can be estimated and is shown to be small (at less than the 1 per cent level). Similarly, the integrated flux of supernovae (SN) is also shown to be insignificant, or at most comparable to MXRBs. AGN therefore remain the most viable candidates for producing the hard XRB, unless additional processes can be shown to dominate the global hard X-ray emission in distant starburst galaxies. 相似文献
17.
《天文和天体物理学研究(英文版)》2017,(10)
XB 1254–690 is a dipping low mass X-ray binary system hosting a neutron star and showing type I X-ray bursts. We aim at obtaining a more accurate orbital ephemeris and at constraining the orbital period derivative of the system for the first time. In addition, we want to better constrain the distance to the source in order to locate the system in a well defined evolutive scenario. We apply, for the first time, an orbital timing technique to XB 1254–690, using the arrival times of the dips present in the light curves that have been collected during 26 yr of X-ray pointed observations acquired from different space missions. We estimate the dip arrival times using a statistical method that weights the count-rate inside the dip with respect to the level of persistent emission outside the dip. We fit the obtained delays as a function of the orbital cycles both with a linear and a quadratic function. We infer the orbital ephemeris of XB 1254–690, improving the accuracy of the orbital period with respect to previous estimates. We infer a mass of M_2 = 0.42 ± 0.04 M_⊙for the donor star, in agreement with estimations already present in literature, assuming that the star is in thermal equilibrium while it transfers part of its mass via the inner Lagrangian point, and assuming a neutron star mass of 1.4 M_⊙. Using these assumptions, we also constrain the distance to the source, finding a value of 7.6±0.8 kpc. Finally, we discuss the evolution of the system, suggesting that it is compatible with a conservative mass transfer driven by magnetic braking. 相似文献
18.
The onset of the confinement transition in the early universe is studied within the Friedmann model. Exploiting a bag model equation of state for the deconfined matter, which is generalized to include also metastable states, the possibility of a mini-inflationary epoch is demonstrated. A criterion of metastability is derived to estimate parameters of this mini-inflation. 相似文献
19.
Rabindra Nath Das 《Astrophysics and Space Science》1978,57(2):409-417
Neutrinos couple through a weak neutral current to the density of matter, in particular to the neutron density. Density fluctuations, or phonons, in the neutron fluid may be emitted or absorbed by neutrinos passing through the matter. At high densities, temperatures and neutrino energies the neutrino mean free paths for phonon emission and absorption can be 106 cm. Significant changes in the neutrino momentum and energy accompany these processes. We present a model calculation for neutrino scattering by phonons, and representative numerical results for the neutrino mean free path and mean energy and momentum changes fork
B
T andE
v both ranging from 1 to 27 MeV.Research supported by the National Research Council of Canada. 相似文献
20.
We present new measurements and modelling of low-resolution transmission spectra of self-broadened ammonia gas, one of the most important absorbers found in the near-infrared spectrum of the planet Jupiter. These new spectral measurements were specifically designed to support measurements of Jupiter's atmosphere made by the Near-Infrared Mapping Spectrometer (NIMS) which was part of the Galileo mission that orbited Jupiter from 1995 to September 2003. To reach approximate jovian conditions in the lab, a new gas spectroscopy facility was developed and used to measure self-broadened ammonia spectra from 0.74 to 5.2 μm, virtually the complete range of the NIMS instrument, for the first time. Spectra were recorded at temperatures varying from 300 to 215 K, pressures from 1000 to 33 mb and using three different path lengths (10.164, 6.164 and 2.164 m). The spectra were then modelled using a series of increasingly complex physically based transmittance functions. 相似文献