共查询到20条相似文献，搜索用时 140 毫秒
1.
E.A. Dorfi 《Astrophysics and Space Science》2000,272(1-3):227-238
Supernova Remnants (SNRs) are the most likely sources of the galactic cosmic rays up to energies of about 1015 eV/nuc. The large scale shock waves of SNRs are almost ideal sites to accelerate particles up to these highly non-thermal
energies by a first order Fermi mechanism which operates through scattering of the particles at magnetic irregularities. In
order to get an estimate on the total amount of the explosion energy E
SNconverted into high energy particles the evolution of a SNR has to be followed up to the final merging with the interstellar
medium. This can only be done by numerical simulations since the non-linear modifications of the shock wave due to particle
acceleration as well as radiative cooling processes at later SNR stages have to be considered in such investigations. Based
on a large sample of numerical evolution calculations performed for different ambient densities n
ext, SN explosion energies, magnetic fields etc. we discuss the final ‘yields’ of cosmic rays at the final SNR stage where the
Mach number of the shock waves drops below 2. At these times the cosmic rays start to diffuse out of the remnant. In the range
of external densities of10-2 ≤ n
ext/[cm-3] ≤ 30 we find a the total acceleration efficiency of about 0.15 E
SN with an increase up to 0.24 E
SN at maximum for an external density of n
ext = 10 cm-3. Since for the larger ambient densities radiative cooling can reduce significantly the total thermal energy content of the
remnant dissipation of Alfvén waves can provide an important heating mechanism for the gas at these later stages. From the
collisions of the cosmic rays with the thermal plasma neutral pions are generated which decay subsequently into observable
γ-rays above 100 MeV. Hence, we calculate these γ-ray luminosities of SNRs and compare them with current upper limits of ground
based γ-raytelescopes. The development of dense shells due to cooling of the thermal plasma increases the γ-ray luminosities
and e.g. an external density of n
ext = 10 cm-3 with E
SN = 1051 erg can lead to a γ-ray flux above 10-6 ph cm-2 s-1 for a remnant located at a distance of 1 kpc.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
We consider the problem of finding the generalized potential function V = U
i(q
1, q
2,..., q
n)q
i + U(q
1, q
2,...;q
n) compatible with prescribed dynamical trajectories of a holonomic system. We obtain conditions necessary for the existence of solutions to the problem: these can be cast into a system of n – 1 first order nonlinear partial differential equations in the unknown functions U
1, U
2,...;, U
n, U. In particular we study dynamical systems with two degrees of freedom. Using adapted coordinates on the configuration manifold M
2 we obtain, for potential function U(q
1, q
2), a classic first kind of Abel ordinary differential equation. Moreover, we show that, in special cases of dynamical interest, such an equation can be solved by quadrature. In particular we establish, for ordinary potential functions, a classical formula obtained in different way by Joukowsky for a particle moving on a surface.Work performed with the support of the Gruppo Nazionale di Fisica Matematica (G.N.F.M.) of the Italian National Research Council. 相似文献
3.
Z. Perjs 《Astronomische Nachrichten》1986,307(5):321-326
In a stationary axisymmetric vacuum gravitational field, the conformal structure of the 3-space is determined by the symmetric, trace free and divergence-less tensor Yir. Using the Killing vector Ki of the axisymmetry, the conformal potential U can be defined by U,i = εijkKjYkrKr. Conversely, the tensor Yik is given algebraically in terms of the gradient U,i of the conformal potential. An attempt is made here to re-formulate the field equations Rλμ = 0 in terms of the conformal potential. Introducing the Ernst potential as a complex coordinate, the cylindrical radius can be eliminated from the field equations. 相似文献
4.
The direct problem of dynamics in two dimensions is modeled by a nonlinear second-order partial differential equation, which is therefore difficult to be solved. The task may be made easier by adding some constraints on the unknown function = f
y
/f
x
, where f(x, y) = c is the monoparametric family of orbits traced in the xy Cartesian plane by a material point of unit mass, under the action of a given potential V(x, y). If the function is supposed to verify a linear first-order partial differential equation, for potentials V satisfying a differential condition, can be found as a common solution of certain polynomial equations.The various situations which can appear are discussed and are then illustrated by some examples, for which the energy on the members of the family, as well as the region where the motion takes place, are determined. One example is dedicated to a Hénon—Heiles type potential, while another one gives rise to families of isothermal curves (a special case of orthogonal families). The connection between the inverse/direct problem of dynamics and the possibility of detecting integrability of a given potential is briefly discussed.This revised version was published online in October 2005 with corrections to the Cover Date. 相似文献
5.
The equations of motion of the 2+2 body problem (two interacting particles in the gravitational field of two much more massive primaries m1 and m2 in circular keplerian orbit) have an integral analogous to the Jacobi integral of the circular 2+1 body problem. We show here that with 2+2 bodies this integral does not give rise to Hill stability, i.e. to confinement for all time in a portion of the configuration space not allowing for some close approaches to occur. This is because all the level manifolds are connected and all exchanges of bodies between the regions surroundingm
1,m
2 and infinity do not contradict the conservation of the integral. However, it is worth stressing that some of these exchanges are physically meaningless, because they involve either unlimited extraction of potential energy from the binary formed by the small bodies (without taking into account their physical size) or significant mutual perturbations between the small masses without close approach, a process requiring, for the Sun-Jupiter-two asteroids system, timescales longer than the age of the Solar System. 相似文献
6.
Xian-Feng Zhao 《Journal of Astrophysics and Astronomy》2011,32(3):391-399
The influence of the potential well depth US(N)U_{\Sigma}^{(N)} of Σ in nuclear matter on the surface gravitational red-shift of a proto neutron star is examined within the framework of
the relativistic mean field theory for the baryon octet system. It is found that as US(N)U_{\Sigma}^{(N)} increases from −35 MeV to +35 MeV, the surface gravitational red-shift increases and the influence of the negative US(N)U_{\Sigma}^{(N)} on the surface gravitational red-shift is larger than that of the positive ones. Furthermore, the M
max/R and the surface gravitational red-shift corresponding to the maximum mass all increase as the US(N)U_{\Sigma}^{(N)} increases, M
max and R being the maximum mass of the proto neutron star and the corresponding radius respectively. 相似文献
7.
Gerold A. Richter 《Astronomische Nachrichten》1974,295(1):27-31
This paper presents a statistical investigation of 999 blue objects [U(–B) 0.00, limiting magnitude U = 20, B = 21], the majority of which is newly discovered on M31-plates (predominantly taken by F. Börngen ) of the large Schmidt telescope of the Karl Schwarzschild Observatory Tautenburg. A list of the objects is given elsewhere [G. A. RICHTER (1973)].For “very blue objects” [(U – B) -0.40] the number per square degree brighter than magnitude B is as follows: log NB = 0.72 B -13.1 (starlike objects), log NB = 0.63 B -12.0 (diffuse and probably diffuse objects). This confirms the results of other authors: log NB increases more rapidly than in the case of constant density (0.6); there are about 10 QSOs brighter than B = 20 per square degree. A detailed discussion concerning the optical identification of discrete radio sources will soon be given. 相似文献
8.
Thierry Combot 《Celestial Mechanics and Dynamical Astronomy》2012,114(4):319-340
We prove an integrability criterion and a partial integrability criterion for homogeneous potentials of degree ?1 which are invariant by rotation. We then apply it to the proof of the meromorphic non-integrability of the n-body problem with Newtonian interaction in the plane on a surface of equation (H, C) = (H 0, C 0) with (H 0, C 0) ?? (0, 0) where C is the total angular momentum and H the Hamiltonian, in the case where the n masses are equal. Several other cases in the 3-body problem are also proved to be non integrable in the same way, and some examples displaying partial integrability are provided. 相似文献
9.
G. Ter-Kazarian 《Astrophysics and Space Science》2010,327(1):91-109
We address gravitation and inertia in the framework of a general gauge principle (GGP) which accounts for the gravitation gauge group
G
R
generated by a hidden local internal symmetry implemented on the flat space. Following the method of phenomenological Lagrangians,
we connect the group G
R
to a non-linear realization of the Lie group of the distortion
G
D
of the local internal properties of six-dimensional flat space, M
6, which is assumed as a toy model underlying four-dimensional Minkowski space. We study the geometrical structure of the space
of parameters and derive the Maurer–Cartan’s structure equations. We treat distortion fields as Goldstone fields, to which
the metric and connection are related, and we infer the group invariants and calculate the conserved currents. The agreement
between the proposed gravitational theory and available observational verifications is satisfactory. Unlike the GR, this theory
is free of fictitious forces, which prompts us to address separately the inertia from a novel view point. We construct a relativistic
field theory of inertia, which treats inertia as a distortion of local internal properties of flat space M
2 conducted under the distortion inertial fields. We derive the relativistic law of inertia (RLI) and calculate the inertial force acting on the photon in a gravitating system. In spite of the totally different and
independent physical sources of gravitation and inertia, the RLI furnishes a justification for the introduction of the Principle
of Equivalence. Particular attention is given to the realization of the group G
R
by the hidden local internal symmetry of the abelian group U
loc=U(1)
Y
×diag[SU(2)], implemented on the space M
6. This group has two generators, the third component T
3 of isospin and the hypercharge Y, implying Q
d
=T
3+Y/2, where Q
d
is the distortion charge operator assigning the number −1 to particles, but +1 to anti-particles. This entails two neutral gauge bosons that coupled
to T
3 and Y. We address the rearrangement of the vacuum state in gravity resulting from these ideas. The neutral complex Higgs scalar
breaks the vacuum symmetry leaving the gravitation subgroup intact. The resulting massive distortion field component may cause
an additional change of properties of the spacetime continuum at huge energies above the threshold value. 相似文献
10.
On closed but non-geometrically similar orbits 总被引：1，自引：1，他引：0
As is well known, the existence of geometrically similar orbits for a particle moving under a central conservative force is a consequence of the fact that the corresponding potential energy is a homogeneous function of the co-ordinates. In this paper, we consider a particular non-homogeneous potential of the form V = U + W, where U and W are homogenous functions of degrees −1 and −2, respectively, because, for this potential, the search of closed orbits, for discrete values of the angular momentum, is straightforward. We focus our attention on these daisy-like charming orbits and graphically show the consequences of the impossibility of geometrical similarity. 相似文献
11.
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
12.
We provide a result of non-analytic integrability of the so-called J
2-problem. Precisely by using the Lerman theorem we are able to prove the existence of a region of the phase space, where the dynamical system exhibits chaotic motions. 相似文献
13.
The second order partial differential equation which relates the potentialV(x,y) to a family of planar orbitsf(x,y)=c generated by this potential is applied for the case of homogeneousV(x,y) of any degreem. It is shown that, if the functionf(x,y) is also homogeneous, there exists, for eachm, a monoparametric set of homogeneous potentials which are the solutions of an ordinary, linear differential equation of the second order. Iff(x,y) is not homogeneous, in general, there is not a homogeneous potential which can create the given family; only if =f
y
/f
x
satisfies two conditions, a homogeneous potential does exist and can be determined uniquely, apart from a multiplicative constant. Examples are offered for all cases. 相似文献
14.
The distribution of radial (U) and rotational (V) velocities of red clump giants was studied as a function of their heights above the galactic plane. The stars of this type
were selected from the compiled catalogue of stellar proper motions and infrared photometry at the north galactic pole with
the use of the diagram “color-reduced proper motion.” According to the data on 1800 red clump giants located at heights from
1 to 3 kpc (mostly thick disk stars), mean kinematic parameters of the thick disk were determined: U
0 = −18 ± 2 km/s, V
0 = −56 ± 1 km/s, σ
U
= 72 ± 2 km/s, and σ
V
= 58 ± 1 km/s. The velocity of asymmetric drift V
0 and velocity variances σ
U
, σ
V
are shown to depend on heights above the galactic plane. 相似文献
15.
We study a model of mergers affecting only the progenitors of present E/SO. We adopt the standard scenarios of star formation as prescribed by Guiderdoni & Rocca-Volmerange. The merging process is parametrized under the assumptions of(1) self-similarity of the Schechter MF and(2) mass conservation. Nine models are discussed. The predictions are compared with counts ofB
J
,U
+,F
+,N
+ bands. E/SO mergers account for the excess of the faintest blue galaxies without causing excess in redder bands. However, as we no longer have enough mergers at brighter magnitudes, a plain E/SO merging model fits less tightly for the redshift and the colour distributions. Detection effect, a steeper slope of LF may be ways to improve. Our models predict acceptable merger frequencies atz = 0.5 although some models predict more interacting galaxies than observation atz = 0. 相似文献
16.
S. Kasperczuk 《Celestial Mechanics and Dynamical Astronomy》1994,58(4):387-391
This paper considers the integrability of generalized Yang-Mills system with the HamiltonianH
a
(p, q)=1/2(p
1
2
+p
2
2
+a
1
q
1
2
+a
2
q
2
2
)+1/4q
1
4
+1/4a
3
q
2
4
+ 1/2a
4
q
1
2
q
2
2
. We prove that the system is integrable for the cases: (A)a
1=a
2,a
3=a
4=1; (b)a
1=a
2,a
3=1,a
4=3; (C)a
1=a
2/4,a
3=16,a
4=6. Our main result is the presentation of these integrals. Only for cases A and B does the Yang-Mills Hamiltonian possess the Painlevé property. Therefore the Painlevé test does not take account of the integrability for the case C. 相似文献
17.
A double discontinuity is a rarely observed compound structure composed of a slow shock layer and an adjoining rotational
discontinuity layer in the downstream region. In this paper, we report the observations of a double discontinuity detected
by Wind on May 15, 1997. This double discontinuity is found to be the front boundary of a magnetic cloud boundary layer. We
strictly identify the shock layer and the rotational discontinuity layer by using the high-resolution plasma and magnetic
field data from Wind. The observed jump conditions of the upstream and downstream region of the slow shock layer are in good
agreement with the Rankine – Hugoniot relations. The flow speeds in the shock frame U
n
<V
Acos θ
Bn
on both sides of the slow shock layer. In the upstream region, the slow Mach number M
s1=U
n1/V
s1 is 1.95 (above unity), and in the downstream region, the slow Mach number M
s2=U
n2/V
s2 is 0.31 (below unity). Here V
A and V
s represent the Alfvén speed and the local slow magnetosonic speed, respectively, and θ
Bn
is the angle between the direction of the magnetic field and the shock normal. The magnetic cloud boundary layer observed
by Wind was also detected by Geotail 48 min later when the spacecraft was located outside the bow shock of the magnetosphere.
However, Geotail observations showed that its front boundary was no longer a double discontinuity and the rotational discontinuity
layer disappeared, indicating that this double discontinuity was unstable when propagating from Wind to Geotail. 相似文献
18.
In this paper we have studied in detail (numerically) the trajectories of charged particles in a magnetic field (dipolar at
infinity) associated with a static star in the framework of Rosen's bimetric theory of gravity. It was found that there do
exist potential wells that allow possible trapping of particles in stable orbits both on and off the equatorial plane. A particularly
interesting feature that has shown up is the fact that the characteristics of the effective potential wellV
eff depend on the ratio of the magnetic field strength parameter λ, and the angular momentumL of the charged particle. For values lower than a critical (λ/L)
c
the potential well lies within the regionr≤2m. 相似文献
19.
Assuming that the formation of the ring current belt is a direct consequence of an enhanced convection of plasma sheet protons, the expression for the energy injection rate UR is formulated as a function of the cross-tail potential drop φCT for a simple electric field-magnetic field model. It is shown that an approximate expression for UR thus formulated consists of two parts: (i) the first part UR1, which is linearly proportional to φCT, is supplied by the corotation electric field and (ii) the second part UR>2, which is proportional to φ2CT, is supplied by the solar wind energy input to the magnetosphere. The second part UR2 dominates the ring current energy input when the cross-tail potential drop φCT is greater than ～ 95 keV, namely during disturbed periods. An important finding is that the second part UR2 of the ring current energy input is shown to be proportional to the solar wind-magnetosphere energy coupling function ?, recovering the observationally established relationship. Therefore, the present study verifies that an enhanced convection is the cause of the ring current formation. 相似文献
20.
R. Zamanov S. Boeva G. Latev K. A. Stoyanov S. V. Tsvetkova 《Astronomische Nachrichten》2015,336(2):189-195
We performed simultaneous observations in 3 bands (U BV) of the flickering variability of the recurrent novae RS Oph and T CrB at quiescence. Using new and published data, we compare the colours of the flickering in cataclysmic variables and symbiotic recurrent novae. We find a difference between the colours of the flickering source in these two types of accreting white dwarfs. The detected difference is highly significant with p ‐values ≈2 x 10–6 for the distributions of (U – B)0 colour and p ≈ 3 x 10–5 on an (U – B) versus (B – V) diagram. The possible physical reasons are briefly discussed. The data are available upon request from the authors. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献