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1.
The equation of radiative acoustics is derived by taking into account the effect of a transverse magnetic field, which is quite similar to the acoustic equation derived in Paper I. The only difference is that theadiabatic, isothermal, andisentropic speeds of sound and theradiation-acoustic speed are replaced by theadiabatic, isothermal, andisentropic magnetoacoustic speeds and theradiation-magnetoacoustic speed, respectively. The main results shown in Paper I are valid even in the presence of a transverse magnetic field. 相似文献
2.
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
3.
The equation of radiative acoustics is derived by taking into account the effect of a non-transverse magnetic field, and the solutions are schematically represented. The main results shown in Paper I and Paper II are valid even in the presence of a non-transverse magnetic field, and the only difference is that theadiabatic, isothermal, andisentropic speeds of sound and theradiation-acoustic speed in Paper I which respectively correspond to theadiabatic, isothermal, andisentropic magnetoacoustic speeds and theradiation-magnetoacoustic speed in Paper II are replaced by the sets of speeds ofadiabatic, isothermal, isentropic, andradiation-acoustic fast andslow waves, respectively. 相似文献
4.
Electromagnetic instabilities in high-β plasmas, where β is the ratio of the kinetic plasma energy to the magnetic energy, have a broad range of astrophysical applications. The presence
of temperature anisotropies T
∥
/T
⊥
>1 (where ∥ and ⊥ denote directions relative to the background magnetic field) in solar flares and the solar wind is sustained by the observations
and robust acceleration mechanisms that heat plasma particles in the parallel direction. The surplus of parallel kinetic energy
can excite either the Weibel-like instability (WI) of the ordinary mode perpendicular to the magnetic field or the firehose
instability (FHI) of the circularly polarized waves at parallel propagation. The interplay of these two instabilities is examined.
The growth rates and the thresholds provided by the kinetic Vlasov – Maxwell theory are compared. The WI is the fastest growing
one with a growth rate that is several orders of magnitude larger than that of the FHI. These instabilities are however inhibited
by the ambient magnetic field by introducing a temperature anisotropy threshold. The WI admits a larger anisotropy threshold,
so that, under this threshold, the FHI remains the principal mechanism of relaxation. The criteria provided here by describing
the interplay of the WI and FHI are relevant for the existence of these two instabilities in any space plasma system characterized
by an excess of parallel kinetic energy. 相似文献
5.
We study the pattern and behavior of a rotating sunspot in Active Region 10930. The rotational angular speed has been extracted
from the apparent motions of the sunspot determined by applying a new optical technique – called non-linear affine velocity
estimator (NAVE) – to high-resolution G-band images taken by the Solar Optical Telescope (SOT) onboard the Hinode satellite. The structure and dynamics of coronal loops in this active region have been examined using the images obtained
by the X-Ray Telescope (XRT) and the spectral data taken by the Extreme-ultraviolet Imaging Spectrometer (EIS), both also onboard Hinode. Our results are summarized as follows: i) The small sunspot of positive polarity rotated counterclockwise about its center by 540° during the period of five days.
ii) Its angular velocity varied with the azimuth angle as well as the radial distance, being affected by the asymmetric shape
of the umbra. iii) The angular velocity increased up to 8° h−1 until 13 December as the sunspot grew, and then decreased rapidly down to 3° h−1 on the next day as the sunspot decayed. iv) The coronal loops that connected the two sunspots became sigmoidal in shape. v) The coronal emissions from the regions around the rotating sunspot were blueshifted, which may indicate the expansion of
the coronal loops. Our results suggest that the rotation of the sunspot may be closely related to the dynamic development
of emerging twisted magnetic fields. 相似文献
6.
A method is proposed allowing a quick self-consistent determination of both the central star parameters (effective temperature, surface gravity, stellar massetc.) and the optical thickness of a planetary nebula (PN). The method is a generalization of the well-known energy balance method. The method has been calibrated and tested using a photoionization model grid computed for this purpose. The internal accuracy of the method is estimated as 0.038dex for the effective temperature of central star and 0.076dex for the surface gravity.The problem of determination of overall energy losses in the nebula required by any kind of energy balance method is considered thoroughly. Approximate expressions are obtained, relating the overall energy losses to the sum of intensities of collisionally excited lines in the optical and ultraviolet spectral ranges and to some other nebular parameters. It is shown that neglecting the energy losses caused by directly unobservable collisional excitation of neutral hydrogen and helium may underestimate the central star temperature by 0.2 or even 0.5dex.
Generalized energy balance method is applied to a sample of 41 PN. Central star temperaturesT
GB
found by this method show an agreement withHeII Zanstra temperaturesT
z
(HeII) whereasT
z
(HI) is always less thanT
GB
or equal to it within the accuracy of the method. So, we confirm the explanation that the well-known Zanstra discrepancy is caused merely by low optical thickness of many PN in the Lyman continuum of hydrogen. The value ofT
z
(HeII) found with modern model atmospheres can be used as good approximation toT
ef
for central stars of overwhelming majority of PN whileT
z
(HI) is usually close toT
ef
for young nebulae only. 相似文献
7.
We performed a detailed analysis of 27 slow coronal mass ejections (CMEs) whose heights were measured in at least 30 coronagraphic
images and were characterized by a high quality index (≥4). Our primary aim was to study the radial evolution of these CMEs
and their properties in the range 2 – 30 solar radii. The instantaneous speeds of CMEs were calculated by using successive
height – time data pairs. The obtained speed – distance profiles [v(R)] are fitted by a power law v = a(R−b)
c
. The power-law indices are found to be in the ranges a=30 – 386, b=1.95 – 3.92, and c=0.03 – 0.79. The power-law exponent c is found to be larger for slower and narrower CMEs. With the exception of two events that had approximately constant velocity,
all events were accelerating. The majority of accelerating events shows a v(R) profile very similar to the solar-wind profile deduced by Sheeley et al. (Astrophys. J.
484, 472, 1997). This indicates that the dynamics of most slow CMEs are dominated by the solar wind drag. 相似文献
8.
In this initial study, we propose a new distance function D
V
involving heliocentric vectorial orbital elements. The function measures differences between: the orbital energies, the angular
momentums vectors and the Laplace vectors. In comparison with the widely used D
SH
criterion of Southworth and Hawkins, D
D
criterion of Drummond and their hybrid D
H
by Jopek, the new function contains one invariant with respect to the principal secular perturbation: the orbital energy.
The new function proved to be useful in the classification amongst the IAU2003 meteoroids which we searched for streams by
D
V
function and also using D
SH
and D
N
-function given by Valsecchi et al. For major streams, the results agree very well. For minor, and near-ecliptical streams
the results sometimes differ markedly. 相似文献
9.
Brenda L. Dingus 《Astrophysics and Space Science》1995,231(1-2):187-190
EGRET on the Compton Gamma Ray Observatory has detected 5 gammaray bursts above 30 MeV. The sub-MeV emission, as detected by BATSE, for these 5 bursts has the largest fluence,F, and peak intensity,I, of any of the BATSE detected bursts within the EGRET field of view. The BATSE data reported in the 2B catalog and the EGRET exposure,E, are combined to select additional bursts with largeF ×E andI ×E. The EGRET data for these bright BATSE bursts are searched for prompt, as well as delayed, emission above 30 MeV. The average properties of the >30 MeV emission are obtained by adding the EGRET data from the 5 bursts. On average the fluence is greater than 15% of the fluence detected by BATSE below an MeV, and the average spectrum is flatter than the spectrum from 1-30 MeV. 相似文献
10.
F. N. Diacu 《Astronomische Nachrichten》1987,308(2):163-168
11.
The stability characteristics of parallel magnetic fields when fluid motions are present along the lines of force is studied. The stability criterion for both symmetric (m=0) and asymmetric (m=1) modes are discussed and the results obtained by Trehan and Singh (1978) are amended in the present study. The results obtained for the cylindrical geometry are shown to play an important role forka<4, wherek is the wave number,a is the radius of the cylinder, compared to the results obtained by Geronicolas (1977) for the slab geometry. 相似文献
12.
Zhanle Du 《Solar physics》2011,273(1):231-253
The shape of each sunspot cycle is found to be well described by a modified Gaussian function with four parameters: peak size
A, peak timing t
m, width B, and asymmetry α. The four-parameter function can be further reduced to a two-parameter function by assuming that B and α are quadratic functions of t
m, computed from the starting time (T
0). It is found that the shape can be better fitted by the four-parameter function, while the remaining behavior of the cycle
can be better predicted by the two-parameter function when using the data from a few (about two) months after the starting
time defined by the smoothed monthly mean sunspot numbers. As a new solar cycle is ongoing, its remaining behavior can be
constructed by the above four- or two-parameter function. A running test shows that the maximum amplitude of the cycle can
be predicted to within 15% at about 25 months into the cycle based on the two-parameter function. A preliminary modeling to
the first 24 months of data available for the current cycle indicates that the peak of cycle 24 may probably occur around
June 2013±7 months with a size of 72±11. The above results are compared to those by quasi-Planck functions. 相似文献
13.
We study the chaotic motions in the field of two fixed black holes M1, M2 by calculating (a) the asymptotic curves from the main unstable periodic orbits, (b) the asymptotic orbits, with particular emphasis οn the homoclinic and heteroclinic orbits, and (c) the basins of attraction of the two black holes. The orbits falling on M1and M2form fractal sets. The asymptotic curves consist of many arcs, separated by gaps. Every gap contains orbits falling on a black hole. The sizes of various arcs decrease as the mass ofM1 increases. The basins of attraction of the black holes M1, M2consist of large compact regions and of thin filaments. The relative area of the basin M2 tends to 100 as M1 → 0, and it decreases as M1 increases. The total area of the basins is found analytically, while the relative area of the basin M2 is given by an empirical formula. Further empirical formulae give the exponential decrease of the number of asymptotic orbits that have not yet reached a black hole after n iterations. 相似文献
14.
Cao Shenglin 《Astrophysics and Space Science》1990,174(2):165-171
According to our Paper I (Cao Shenglin, 1988), it could be supposed that the physical space-time is a Finsler space-time, characterized by the metric ds
4=g
ijkf
dx
i
dx
j
dx
k
dx
f
. If so, a new space-time transformation could be found by invariant ds
4 and the theory of relativity is discussed on this transformation.The project supported by National Natural Science Foundation of China. 相似文献
15.
For monoparametric familiesf(x,y)=c of planar orbits, created by a planar potentialV(x,y), we introduce the notion of the family boundary curves (FBC). All members of the familyf(x,y)=c are traced in an allowable region of thexy plane, defined by the corresponding FBC, with total energyE=E(c) varying along the family. Family boundary curves are also found for two-parametric familiesf(x,y,b)=c. The relation of equilibrium points and asymptotic orbits, possibly possessed by the potentialV(x,y), to be FBC is studied. 相似文献
16.
The dynamics of space debris with very high A/m near the geostationary orbit is dominated by the gravitational coefficient C
22 and the solar radiation pressure. An analysis of the stability of the orbits by the chaos indicator MEGNO and frequency analysis map FAM shows chaotic layers around the separatrix and reveals a web of sub-structures associated to resonances with the annual period
of the Sun. This succession of stable thin islands and chaotic layers can be reproduced and explained by a quite simple toy
model, based on a pendulum approach, perturbed, through the eccentricity, by the external (Sun) frequency. The use of suitable
action-angle variables in the circulation and libration regions of the pendulum allows to point out new resonances between
the geostationary libration angle and the Sun’s longitude. They correspond very well (positions, shape, width) to the structures
visible on the FAM representations. 相似文献
17.
F. Partal Ureña M. Fernández Gómez J.J. López González N. Rajamanickam 《Astrophysics and Space Science》2000,272(4):345-352
The Franck-Condon (FC) factors and r-centroids for the bands systemC
1
Σ
+
→ X
1
Σ
+ of AlD and E
2
Π → X
2
Σ
+ of CaH have been evaluated by means of a reliable numerical integration procedure by using a suitable potential. The dissociation
energy, D
e, for the electronic ground states of AlD and CaH have been estimated by the curve fitting method to the RKRV experimental
potential curve turning out to be 3.01 eV and 2.32 eV, respectively.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
18.
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
19.
The debate concerning the viability of f(R)-gravity as a natural extension of General Relativity could be realistically addressed by using results coming from binary pulsars like PSR 1913 + 16. To this end, we develop a quadrupolar approach to the gravitational radiation for a class of analytic f(R)-models. We show that experimental results are compatible with a consistent range of f(R)-models. This means that f(R)-gravity is not ruled out by the observations and gravitational radiation (in strong field regime) could be a test-bed for such theories. 相似文献
20.
The free molecular flow over an infinite oscillating plane wall under external periodic force is considered. The Boltzmann equation is solved by using moments method with two-stream distribution functions. The boundary condition is obtained by assuming that the reflection of the particles from the solid surface takes place with complete energy accommodation. An analytical form for the velocity (X) and shear stress (Y) at any point is obtained. The results show that the amplitude of both the velocity change (X
1) and the shear stress change (Y
1) due to the periodic external force at the boundary (y=0) is an increasing function of time (t). 相似文献