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1.
We explore self-similar hydrodynamic evolution of central voids embedded in an isothermal gas of spherical symmetry under
the self-gravity. More specifically, we study voids expanding at constant radial speeds in an isothermal gas and construct
all types of possible void solutions without or with shocks in surrounding envelopes. We examine properties of void boundaries
and outer envelopes. Voids without shocks are all bounded by overdense shells and either inflows or outflows in the outer
envelope may occur. These solutions, referred to as type
void solutions, are further divided into subtypes
and
according to their characteristic behaviours across the sonic critical line (SCL). Void solutions with shocks in envelopes
are referred to as type
voids and can have both dense and quasi-smooth edges. Asymptotically, outflows, breezes, inflows, accretions and static outer
envelopes may all surround such type
voids. Both cases of constant and varying temperatures across isothermal shock fronts are analyzed; they are referred to as
types
and
void shock solutions. We apply the ‘phase net matching procedure’ to construct various self-similar void solutions. We also
present analysis on void generation mechanisms and describe several astrophysical applications. By including self-gravity,
gas pressure and shocks, our isothermal self-similar void (ISSV) model is adaptable to various astrophysical systems such
as planetary nebulae, hot bubbles and superbubbles in the interstellar medium as well as supernova remnants.
相似文献
2.
The measurements of pulsar frequency second derivatives have shown that they are 102−106 times larger than expected for standard pulsar spin-down law, and are even negative for about half of pulsars. We explain
these paradoxical results on the basis of the statistical analysis of the rotational parameters ν,
and
of the subset of 295 pulsars taken mostly from the ATNF database. We have found a strong correlation between
and
for both
and
, as well as between ν and
. We interpret these dependencies as evolutionary ones due to
being nearly proportional to the pulsars’ age. The derived statistical relations as well as “anomalous” values of
are well described by assuming the long-time variations of the spin-down rate. The pulsar frequency evolution, therefore,
consists of secular change of ν
ev(t),
and
according to the power law with n≈5, the irregularities, observed within a timespan as a timing noise, and the variations on the timescale larger than that—several
decades.
This work has been supported by the Russian Foundation for Basic Research (grant No 04-02-17555), Russian Academy of Sciences
(program “Evolution of Stars and Galaxies”), and by the Russian Science Support Foundation. The authors would also like to
thank the anonymous referee for valuable comments. 相似文献
3.
Using Damour-Ruffini’s and Hamilton-Jacobi’s methods, Hawking radiation from a Vaidya black hole is investigated. Due to non-stationary
black holes, the event horizon r
H
and the entropy S are all related to both the mass m(υ) and
. When the back-reaction of particles’s energy to space-time is considered, we get the emission probability. It is found that
the result is different from that of the stationary Schwarzschild black hole, because
is the function of mass m(υ).
相似文献
4.
In this paper we have considered the Universe to be filled with Modified Gas and the Cosmological Constant Λ to be time-dependent
with or without the Gravitational Constant G to be time-dependent. We have considered various phenomenological models for Λ, viz.,
and
. Using these models it is possible to show the accelerated expansion of the Universe at the present epoch. Also we have shown
the natures of G and Λ over the total age of the Universe. Using the statefinder parameters we have shown the diagrammatical representation
of the evolution of the Universe starting from radiation era to ΛCDM model. 相似文献
5.
In this paper, dilaton in Weyl-Scaled induced gravitational theory is regarded as a candidate of dark energy. When the potential of dilaton field is taken as the form of a double exponential , we find that there exist attractor solutions in dilatonic dark energy model, and these attractors correspond to an equations of state and a cosmic density parameter , which are important features for a dark energy model that can meet the current observations. We find out the sufficient condition of the existence of a late time de Sitter attractor. 相似文献
6.
A. S. Al-Rawaf 《Astrophysics and Space Science》2007,310(1-2):173-175
Due to the recent all-sky, high-precision measurement of microwave background anisotropies by WMAP, a value for baryon-to-photon
ratio η was obtained. At the WMAP value for η, the 4HE abundance was predicted. In this article we use a simple semi-analytical method with 4He predicted and measured values to place a limit on the variation of the gravitational constant G. We find using a conservative range for the measured values for Y
p
, that ΔG/G is constrained between −0.26 and 0.15. If we assume a monotonic power law time dependence G∼t
−β
then β values is constrained between −0.008 and 0.0038, which translate into
. This compares well with results obtained by others using full numerical analysis.
相似文献
7.
G. A. Krasinsky 《Celestial Mechanics and Dynamical Astronomy》2008,101(4):325-336
The long-term systematic errors of the analytical theories IAU 2000 and IAU 2006 of the Earth’s precession–nutational motion
are studied making use of the VLBI data of 1984–2007. Several independent methods give indubitable evidence of the significant
quadratic error in the IAU 2000 residuals of the precessional angle while the adopted value of the secular decrease /cy of the Earth’s ellipticity e (derived from Satellite Laser Ranging data) should manifest itself in the residuals of as the negative quadratic trend . The problem with the precession of the IAU 2006 theory adopted as a new international standard and based on the precession
model P03 (Capitaine et al., Astron Astrophys 432:355–367, 2005) appears to be even more serious because the above mentioned quadratic term has already been incorporated into the P03 precession. Our analysis of the VLBI data demonstrates that the quadratic trend
of the IAU 2006 residuals does amount to the expected value (30.0 ± 3) mas/cy2. It means, first, that the theoretical precession rate of IAU 2006 should be augmented by the large secular correction and, second, that the available VLBI data have potentiality of estimating the rate . And indeed, processing these data by the numerical theory ERA of the Earth’s rotation (Krasinsky, Celest Mech Dyn Astron
96:169–217, 2006, Krasinsky and Vasilyev, Celest Mech Dyn Astron 96:219–237, 2006) yields the estimate /cy statistically in accordance with the satellite-based . On the other hand, applying IAU 2000/2006 models, the positive value /cy is found which is incompatible with the SLR estimate and, evidently, has no physical meaning. The large and steadily increasing
error of the precession motion of the IAU 2006 theory makes the task of replacing IAU 2006 by a more accurate model be most
pressing. 相似文献
8.
V. V. Ivanov 《Astrophysics》2009,52(1):24-39
This is a discussion of V. A. Ambartsumyan’s studies of the mean number of scatterings for photons in scattering media and
of further work and development in this area, especially at Ambartsumyan’s St. Petersburg school. The following questions
are discussed briefly: (a) the traditional method for calculating the number of scatterings from the source function and critiques
of this method. (b) The equation for the number N(τ; τ0 ) of scatterings for a photon born at optical depth τ in a plane layer of optical thickness τ0 and its use for calculating the number of scatterings, averaged over the entire ensemble of photons for a medium with arbitrary internal sources. These questions
are first considered for the case of monochromatic scattering, and then for scattering in a spectral line with complete frequency
redistribution (CFR). (c) The mean path length for a resonance line photon in a scattering medium with CFR and continuum absorption: the basic equations and asymptotic
behavior of an optically thick layer. (d) A review of calculations of and in media that are so thick that the CFR approximation breaks down and the effects of partial frequency redistribution (PFR)
become dominant. The presentation is at a semiquantitative level in many parts of this paper, with stress on physical significance
rather than the mathematics, through the use of approximate and asymptotic solutions.
Translated from Astrofizika, Vol. 52, No. 1, pp. 29–45 (February 2009). 相似文献
9.
A. Z. Bonanos K. Z. Stanek R. P. Kudritzki L. Macri D. D. Sasselov J. Kaluzny D. Bersier F. Bresolin T. Matheson B. J. Mochejska N. Przybilla A. H. Szentgyorgyi J. Tonry G. Torres 《Astrophysics and Space Science》2006,304(1-4):207-209
We present the first direct distance determination to a detached eclipsing binary in M33, which was found by the DIRECT Project. Located in the OB 66 association, it was one of the most suitable detached eclipsing binaries found by DIRECT for distance determination, given its 4.8938 day period. We obtained follow-up BV photometry and spectroscopy from which we determined the parameters of the system. It contains two O7 main sequence stars with masses of and and radii of and , respectively. We derive temperatures of K and K and determine the reddening . Using HST photometry for flux calibration in the V band, we obtain a preliminary distance modulus of mag ( kpc). The photometry and thus distance is subject to revision in the final paper. 相似文献
10.
M. S. Wheatland 《Solar physics》2009,255(2):211-227
A Monte Carlo approach to solving a stochastic-jump transition model for active-region energy (Wheatland and Glukhov: Astrophys. J.
494, 858, 1998; Wheatland: Astrophys. J.
679, 1621, 2008) is described. The new method numerically solves the stochastic differential equation describing the model, rather than the
equivalent master equation. This has the advantages of allowing more efficient numerical solution, the modeling of time-dependent
situations, and investigation of details of event statistics. The Monte Carlo approach is illustrated by application to a
Gaussian test case and to the class of flare-like models presented in Wheatland (Astrophys. J.
679, 1621, 2008), which are steady-state models with constant rates of energy supply, and power-law distributed jump transition rates. These
models have two free parameters: an index (δ), which defines the dependence of the jump transition rates on active-region energy, and a nondimensional ratio (
) of total flaring rate to rate of energy supply. For
the nondimensional mean energy
of the active-region satisfies
, resulting in a power-law distribution of flare events over many decades of energy. The Monte Carlo method is used to explore
the behavior of the waiting-time distributions for the flare-like models. The models with δ≠0 are found to have waiting times that depart significantly from simple Poisson behavior when
. The original model from Wheatland and Glukhov (Astrophys. J.
494, 858, 1998), with δ=0 (i.e., no dependence of transition rates on active-region energy), is identified as being most consistent with observed flare statistics. 相似文献
11.
Arbab I. Arbab 《Astrophysics and Space Science》2009,323(2):181-184
In the framework of unifying gravity and electromagnetism, we have shown that accelerating objects emit gravitational wave
as those determined by Larmor formula for the accelerating charged particle. We have found new formulae for the power of Gravitational
waves radiated by spinning and orbiting objects. The minimum wavelength of the gravitational wave emitted by an object of
mass m and radius R is
. 相似文献
12.
H. Rovithis-Livaniou 《Astrophysics and Space Science》1977,52(2):271-306
The aim of the present paper is to find the eclipse perturbations, in the frequency-domain, of close eclipsing systems exhibiting partial eclipses.After a brief introduction, in Section 2 we shall deal with the evaluation of thea
n
(l)
integrals for partial eclipses and give them in terms ofa
0
0
,a
0
0
(of the associated -functions) and
integrals; while Section 3 gives the eclipse perturbations
arising from the tidal and rotational distortion of the two components. The
are given for uniformly bright discs (h=1) as well as for linear and quadratic limb-darkening (h=2 and 3, respectively).Finally, Section 4 gives a brief discussion of the results and the way in which they can be applied to practical cases. 相似文献
13.
14.
Contribution of Vacuum Field to Angular Deviation of Light Path and Radar Echo Delay 总被引：3，自引：0，他引：3
The discovery of ‘twin quasistellar objects’ arose interests among astronomers and astrophysicists to study gravitational
lensing problems. The deviation of light from its straight line path is caused by two sources according to the general theory
of relativity: (i) the presence of massive objects, i.e. the presence of gravitational field and (ii) the presence of a ‘vacuum
field’ which arises because there is a non-zero cosmological vacuum energy. Recently, the research on the relationship between
cosmological constant and gravitational lensing process is rather active (see reference [1, 2, 3]. According to the Kottler
space time metric, we have deduced an explicit representation of the angular deviation of light path. The deviation term is
found to be simply
, where M is the mass of the ‘astronomical lens’, rmin is the distance between the point of nearest approach and the centre of M, other symbols have their usual meaning. The presence
of this term may be meaningful to the study of cosmological constant using the concept of gravitational lensing; however more
sophisticated analysis awaits. Consider a signal radar to be sent from one planet to another. We have found that the radar
echo delay contributed by the existence of the cosmological constant Λ is expressible as
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
15.
16.
We report on 10 yr of monitoring of the 8.7-s Anomalous X-ray Pulsar 4U 0142+61 using the Rossi X-Ray Timing Explorer (RXTE). This pulsar exhibited stable rotation from 2000 until February 2006: the RMS phase residual for a spin-down model which
includes ν,
, and
is 2.3%. We report a possible phase-coherent timing solution valid over a 10-yr span extending back to March 1996. A glitch
may have occurred between 1998 and 2000, but it is not required by the existing data. We also report that the source’s pulse
profile has been evolving in the past 6 years, such that the dip of emission between its two peaks has been getting shallower
since 2000, almost as if the profile is recovering to its pre-2000 morphology, in which there was no clear distinction between
the peaks. These profile variations are seen in the 2–4 keV band but not in 6–8 keV. Finally, we present the pulsed flux time
series of the source in 2–10 keV. There is evidence of a slow but steady increase in the source’s pulsed flux since 2000.
The pulsed flux variability and the narrow-band pulse profile changes present interesting challenges to aspects of the magnetar
model.
This work was supported by the Natural Sciences and Engineering Research Council (NSERC) PGSD scholarship to R.D. F.P.G. holds
a National Research Council Research Associateship Award at NASA Goddard Space Flight Center. Additional support was provided
by NSERC Discovery Grant Pgpin 228738-03 NSERC Steacie Supplement Smfsu 268264-03, FQRNT, CIAR, and CFI. V.M.K. is a Canada
Research Chair. 相似文献
17.
Anirudh Pradhan G. S. Khadekar Deepak Srivastava 《Astrophysics and Space Science》2006,305(4):415-421
Implications of cosmological model with a cosmological term of the form , where β is a constant, are analyzed in multidimensional space time. The proper distance, the luminosity distance-redshift, the angular diameter distance-redshift, and look back time-redshift for the model are presented. It has been shown that models are found to be compatible with the present observations. This work, has thus generalized to higher dimensions the well-known result in four dimensional space time. It is found that the difference is significant at least in the principal to the anologous situation in four dimensional space time. 相似文献
18.
We perform the bifurcation analysis of the Kepler problem on
and
. An analog of the Delaunay variables is introduced. We investigate the motion of a point mass in the field of a Newtonian
center moving along a geodesic on
and
(the restricted two-body problem). For the case of a small curvature, the pericenter shift is computed using the perturbation
theory. We also present the results of numerical analysis based on an analogy with the motion of a rigid body. 相似文献
19.
The photometric elements of the Algol type binary TT Hydrae derived by the authors from theirUBV observations during 1973–77 have been combined with the spectroscopic elements given by Sanford (1937) and Sahade and Cesco
(1946) to obtain the absolute dimensions of the system. It is found that the spectroscopic orbital elements given by Sanford
represent the evolutionary status of the secondary component better than those of Sahade and Cesco. The primary appears to
be an Al v main sequence star of mass
and radius ∼2.3R
⊙. The secondary fills its Roche lobe; it can be represented by a K0iii star of mass
and radius ∼6.0R
⊙. Better spectroscopic data are needed for confirmation of these results. 相似文献
20.
A linear excitation of electromagnetic modes at frequencies
, in a plasma through which two electron beams are contra-streaming along the magnetic field is investigated. This may be a source of the observed
emissions at auroral latitudes. 相似文献