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1.
The regularization of a new problem, namely the three-body problem, using ‘similar’ coordinate system is proposed. For this
purpose we use the relation of ‘similarity’, which has been introduced as an equivalence relation in a previous paper (see
Roman in Astrophys. Space Sci. doi:, 2011). First we write the Hamiltonian function, the equations of motion in canonical form, and then using a generating function,
we obtain the transformed equations of motion. After the coordinates transformations, we introduce the fictitious time, to
regularize the equations of motion. Explicit formulas are given for the regularization in the coordinate systems centered
in the more massive and the less massive star of the binary system. The ‘similar’ polar angle’s definition is introduced,
in order to analyze the regularization’s geometrical transformation. The effect of Levi-Civita’s transformation is described
in a geometrical manner. Using the resulted regularized equations, we analyze and compare these canonical equations numerically,
for the Earth-Moon binary system. 相似文献
2.
In this paper it is suggested that inclusion of mutual gravitational interactions among the particles in the early dense universe
can lead to a ‘pre-big bang’ scenario, with particle masses greater than the Planck mass implying an accelerating phase of
the universe, which then goes into the radiation phase when the masses fall below the Planck mass. The existence of towers
of states of such massive particles (i.e. multiples of Planck mass) as implied in various unified theories, provides rapid
acceleration in the early universe, similar to the usual inflation scenario, but here the expansion rate goes over ‘smoothly’
to the radiation dominated universe when temperature becomes lower than the Planck temperature. 相似文献
3.
Ashok Ambastha 《Journal of Astrophysics and Astronomy》1984,5(3):285-306
We have studied the stability of finite gaseous discs, against large-scale perturbations, under the influence of spherical,
massive haloes. A surface-density distribution consistent with the observed spiral-tracer profiles in disc galaxies is considered
for the disc. We find that growing eigenmodes with both ‘trailing’ and ‘leading’ spirals exist in ‘cold’ discs for a wide
range of values of the halo mass and its radius. The amplification rates of the unstable modes reduce as the ratio of the
mass of the halo to the mass of the disc is increased. A uniform halo is not very effective towards stabilizing the disc against
these modes. The results from the present study are consideredvis-a-vis previous studies on the global modes of self-gravitating discs. 相似文献
4.
B. Albayrak G. Djurašević S. Selam M. Yilmaz S. Erkapić O. Aksu T. Tanriverdi 《Astrophysics and Space Science》2005,296(1-4):293-296
BVR light curves of the recently discovered eclipsing binary V351 Peg were studied to derive the preliminary physical parameters
of the system. The light curves were obtained at the TüBİTAK* – Turkish National Observatory (TUG) during three nights in
August, 2003. The solutions were made using Djurašević’s inverse problem method. V351 Peg is a system in an overcontact configuration
(f
over∼ 21 %) with a relatively small temperature difference between the components ΔT ≈ 20 K. The results suggest a significant mass and energy transfer from the more massive primary onto the less massive secondary.
The hot area on the less massive star, near the neck region, can be considered as a consequence of this mass and energy exchange
between the components through the connecting neck of the common envelope.
TüBİTAK: The Scientific and Technical Research Council of Turkey. 相似文献
5.
In recent years there has been much debate, both observational and theoretical, about the nature of star formation at high
redshift. In particular, there seems to be strong evidence of a greatly enhanced star formation rate early in the Universe’s
evolution. Simulations investigating the nature of the first stars indicate that these were large, with masses in excess of
100 solar masses. By the use of a chemical model, we have simulated the molecular signature of massive star formation for
a range of redshifts, using different input models of metallicity in the early Universe. We find that, as long as the number
of massive stars exceeds that in the Milky Way by factor of at least 1000, then several ‘hot-core’ like molecules should have
detectable emission. Although we predict that such signatures should already be partly detectable with current instruments
(e.g. with the VLA), facilities such as ALMA will make this kind of observation possible at the highest redshifts. 相似文献
6.
We present a study of the effects of atmospheric seeing on quantities derived from observations of solar polarized light –
specifically, the vector magnetic flux and quantities derived from its magnitude and direction. Data from the Imaging Vector
Magnetograph (‘IVM’) at the U. Hawaii/Mees Solar Observatory, are degraded by various degrees by applying a blur function
to the ‘incoming light’, simulating a range of seeing conditions. A quantitative study of the resulting effects on derived
quantities including total magnetic flux, vertical electric current density and magnetic shear angles, are discussed as a
function of the imposed degradation. The generality of the seeing effects is explored by comparing the results from two different
active regions; we find that the results are comparable for those quantities directly computed from the magnetic flux vector
(e.g., summed, as in total flux) but less so for those quantities involving higher-order calculations (e.g., derivatives,
as in vertical currents). We suggest that for temporal series data from any instrument, a method such as that which we outline
here, be applied in order to model the uncertainties imposed on the data (in addition to instrumental uncertainties, etc.)
due to seeing variations. 相似文献
7.
Michael Nowak 《Astrophysics and Space Science》2005,300(1-3):159-166
Previous work by Motch et al. [1985, Space Sci. Rev. 40, 219] suggested that in the low/hard state of GX, the soft X-ray power-law extrapolated backward in energy agrees with the
IR flux level. Corbel and Fender [2002, ApJ 573, L35–L39] later showed that the typical hard state radio power-law extrapolated forward in energy meets the backward extrapolated
X-ray power-law at an IR spectral break, which was explicitly observed twice in GX. This has been cited as further evidence
that jet synchrotron radiation might make a significant contribution to the observed X-rays in the hard state. We explore
this hypothesis with a series of simultaneous radio/X-ray hard state observations of GX. We fit these spectra with a simple,
but remarkably successful, doubly broken power-law model that indeed requires a spectral break in the IR. For most of these
observations, the break position as a function of X-ray flux agrees with the jet model predictions. We then examine the radio
flux/X-ray flux correlation in CYG through the use of 15 GHz radio data, obtained with the Ryle radio telescope, and Rossi X-ray Timing Explorer data, from the All Sky Monitor and pointed observations. We find evidence of ‘parallel tracks’ in the radio/X-ray correlation which are associated with
‘failed transitions’ to, or the beginning of a transition to, the soft state. We also find that for CYG the radio flux is
more fundamentally correlated with the hard, rather than the soft, X-ray flux. 相似文献
8.
Michael A. Dopita Lawrence M. Krauss Ralph S. Sutherland Chiaki Kobayashi Charles H. Lineweaver 《Astrophysics and Space Science》2011,335(2):345-352
Recent observations show that the measured rates of star formation in the early universe are insufficient to produce re-ionization,
and therefore, another source of ionizing photons is required. In this Letter, we examine the possibility that these can be supplied by the fast accretion shocks formed around the cores of the most massive
haloes (10.5<log M/M
⊙<12) on spatial scales of order 1 kpc. We model the detailed physics of these fast accretion shocks, and apply these to a
simple 1-D spherical hydrodynamic accretion model for baryonic infall in dark matter halos with an Einasto density distribution.
The escape of UV photons from these halos is delayed by the time taken to reach the critical accretion shock velocity for
escape of UV photons; 220 km s−1, and by the time it takes for these photons to ionize the surrounding baryonic matter in the accretion flow. Assuming that
in the universe at large the baryonic matter tracks the dark matter, we can estimate the epoch of re-ionization in the case
that accretion shocks act alone as the source of UV photons. We find that 50% of the volume (and 5-8% of the mass) of the
universe can be ionized by z∼7–8. The UV production rate has an uncertainty of a factor of about 5 due to uncertainties in the cosmological parameters
controlling the development of large scale structure. Because our mechanism is a steeply rising function of decreasing redshift,
this uncertainty translates to a re-ionization redshift uncertainty of less than ±0.5. We also find that, even without including
the UV photon production of stars, re-ionization is essentially complete by z∼5.8. Thus, fast accretion shocks can provide an important additional source of ionizing photons in the early universe. 相似文献
9.
This study is part of an investigation of the possibility of using chemically peculiar (CP) stars to map local galactic structure.
Correct luminosities of these stars are therefore crucial. CP stars are generally regarded as main-sequence or near-main-sequence
objects. However, some CP stars have been classified as giants.
A selection of stars, classified in literature as CP giants, are compared to normal stars in the same effective temperature
interval and to ordinary ‘non giant’ CP stars. We find no clear confirmation of a higher luminosity for ‘CP giants’, than
for CP stars in general. In addition, CP characteristics seem to be individual properties not repeated in a component star
or other cluster members. 相似文献
10.
Enrique Guzmán 《Astrophysics and Space Science》1997,253(1):7-12
By solving a Wheeler-De Witt ‘extended’ equation in the Brans-Dicke theory, we have found that the probability distribution
predicts: i) An initial value for the Brans-Dicke scalar field φ ∼ ρ1/2_VAC in the beginning of the inflation, where ρVAC is the vacuum density energy (this gives a planck mass ∼ ρ1/4_VAC) ii) Large values for the Brans-Dicke parameter w. On the other hand it is shown that by taking into account the dynamical
behaviour of φ and the matter scalar field σ we can formulate a ‘creation boundary condition’ where in the ‘beginning’ of
the Universe (R =0, ‘nothing’ for some authors) we have a dynamical σ already ‘created’. This could be the energetic mechanism
which makes Universe tunnels the potential barrier to evolve classically after. Besides we have found the possibility of a
cosmological uncertainty principle.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
We present a comparative study of low-l solar p-mode parameters extracted by genetic-algorithm and ‘standard’ hill-climbing minimisation routines. To effect this we make
use of observations made in integrated sunlight by the Birmingham Solar-Oscillations Network (BiSON) and the GOLF instrument
on board the ESA/NASA SOHO satellite, in addition to artificial data. We find that over the central part of the p-mode range the two fitting routines return similar results. However, at low frequencies — where the S/N in the modes is low
and their resonant peaks narrow — we find that the genetic routine appears to offer more robust estimates of the underlying
parameters. 相似文献
12.
In a previous work we studied the effects of (I) the J
2 and C
22 terms of the lunar potential and (II) the rotation of the primary on the critical inclination orbits of artificial satellites.
Here, we show that, when 3rd-degree gravity harmonics are taken into account, the long-term orbital behavior and stability
are strongly affected, especially for a non-rotating central body, where chaotic or collision orbits dominate the phase space.
In the rotating case these phenomena are strongly weakened and the motion is mostly regular. When the averaged effect of the
Earth’s perturbation is added, chaotic regions appear again for some inclination ranges. These are more important for higher
values of semi-major axes. We compute the main families of periodic orbits, which are shown to emanate from the ‘frozen eccentricity’
and ‘critical inclination’ solutions of the axisymmetric problem (‘J
2 + J
3’). Although the geometrical properties of the orbits are not preserved, we find that the variations in e, I and g can be quite small, so that they can be of practical importance to mission planning. 相似文献
13.
Richard A. Harrison 《Solar physics》1997,175(2):467-485
A search for microflare activity in the extreme ultraviolet (EUV) quiet Sun using the Coronal Diagnostic Spectrometer (CDS)
aboard the Solar and Heliospheric Observatory (SOHO) spacecraft has not resulted in the identification of microflare activity,
but has resulted in the identification of a hitherto unknown phenomenon: enhancements of a factor of 2–3 in the flux of transition
region lines at network junctions. A total of some 6 hours of observation of 5 different target areas showed this ‘blinker’
activity at each area, with durations ranging from 1 to 30 min and averaging 13 min, and thermal energy content of order 10-6 that of a ‘standard’ flare. Assuming that the observations are of typical quiet Sun, and projecting these data to predict
a distribution of these events over the entire Sun, the total thermal energy content of these ‘blinkers’ is insignificant
when compared to the energy required to heat the corona. The nature of these events and their significance are discussed in
this paper. 相似文献
14.
Ajoy Kumar Dasgupta 《Astrophysics and Space Science》1980,67(1):247-253
Charged dust grains of radiia≃3×10−6∼3×10−5 cm could be a help in understanding high energy particles in extensive air showers (EAS). It is suggested that the dust grains
in the intergalactic medium may attain relatistic energy (≥1020 eV), and may be responsible for the apparent ‘bump’ in the energy spectrum. The relativistic and non-relativistic dust grains
may help to understand the anomalies in the energy spectrum as regards the slope and intensity. 相似文献
15.
G. Djurašević O. Demircan S. Özdemir M. Tanriver Z. Müyesseroglu H. Ak B. Albayrak 《Astrophysics and Space Science》1997,253(2):265-274
The UBV observations of the massive binary BF Aur were made at the Ankara University Observatory during 1988, 1989 and 1996.
Asymmetry of the light curves, arising from unequal height of successive maxima, indicates that the system is active. By analysing
these observations in the framework of the Roche model (including the presence of bright regions on the components) one obtains
a semidetached configuration of the system, with the cooler secondary component filling its Roche lobe. The analysis of the
light curves yields consistent solutions for mass ratio q = m2/m1 somewhat less than one. The influence of the mass transfer on the change of the system-orbital-period is relatively small.
The upward parabolic character of the O–C diagram (Zhang et al., 1993) indicates a mass transfer from the less massive secondary
to the more massive primary. This inturn requires the less massive secondary to fill its Roche lobe. This is consistent with
our solution. Based on these facts we introduced the following working hypothesis. At the place where the gas stream from
the secondary falls on the primary, relatively small in size but a high temperature contrast active hot-spot (hs) region is
formed. As a result of the heating effect caused by the irradiation of the hot-spot region, on the secondary's side facing
the hot spot a bright-spot (bs) region is formed. The bright-spot region is larger in size but with significantly lower temperature
than the hot spot. This region can be treated as a ‘reflection cap’. By analysing the light curves in the framework of this
working hypothesis the basic parameters of the system and the active regions are estimated. The problem is solved in two stages:
by obtaining a synthetic light curve in the case when the parameters of the corresponding Close Binary (CB) Roche model (Djurašević,
1992a) are given a priori (the direct problem) and by determining the parameters of the given model for which the best fit
between the synthetic light curve and the observations is achieved (the inverse problem) (Djurašević, 1992b).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
E. P. J. van den Heuvel 《Journal of Astrophysics and Astronomy》1995,16(2):255-288
The evolution of high-and low-mass X-ray binaries (HMXB and LMXB) into different types of binary radio pulsars, the ‘high-mass
binary pulsars’(HMBP) and ‘low-mass binary pulsars’ (LMBP) is discussed. The HMXB evolve either into Thorne-Zytkow objects
or into short-period binaries consisting of a helium star plus a neutron star (or a black hole), resembling Cygnus X-3. The
latter systems evolve (with or without a second common-envelope phase) into close binary pulsars, in which the companion of
the pulsar may be a massive white dwarf, a neutron star or a black hole ( some final systems may also consist of two black
holes). A considerable fraction of the systems may also be disrupted in the second supernova explosion. We discuss the possible
reasons why the observed numbers of double neutron stars and of systems like Cyg X-3 are several orders of magnitude lower
than theoretically predicted. It is argued that the observed systems form the tip of an iceberg of much larger populations
of unobserved systems, some of which may become observable in the future. As to the LMBP, we consider in some detail the origins
of systems with orbital periods in the range 1–20 days. We show that to explain their existence, losses of orbital angular
momentum (e.g., by magnetic braking) and in a number of cases: also of mass, have to be taken into account. The masses of
the low-mass white dwarf companions in these systems can be predicted accurately. We notice a clear correlation between spin
period and orbital period for these systems, as well as a clear correlation between pulsar magnetic field strength and orbital
period. These relations strongly suggest that increased amounts of mass accreted by the neutron stars lead to increased decay
of their magnetic fields: we suggest a simple way to understand the observed value of the ‘bottom’ field strengths of a few
times 108 G. Furthermore, we find that the LMBP-systems in which the pulsar has a strong magnetic field (> 1011 G) have an about two orders of magnitude larger birth rate (i.e., about 4 × 10-4 yr-1 in the Galaxy) than the systems with millisecond pulsars (which have B < 109 G). Using the observational fact that neutron stars receive a velocity kick of ∼450 km/s at birth, we find that some 90%
of the potential progenitor systems of the strong-field LMBP must have been disrupted in the Supernovae in which their neutron
stars were formed. Hence, the formation rate of the progenitors of the strong-field LMBP is of the same order as the galactic
supernova rate (4 × 10-3 yr-1). This implies that a large fraction of all Supernovae take place in binaries with a close low-mass (< 2.3 M⊙) companion. 相似文献
17.
Martin J. Rees 《Journal of Astrophysics and Astronomy》1984,5(4):331-348
The evidence for unseen mass (which is briefly reviewed) suggests that the cosmological density parameter Ω is at least 0.1–0.2.
An Einstein-de-Sitter ‘flat’ universe with Ω = 1 — which is appealing for theoretical reasons — can only be reconciled with
the data if the galaxies are more ‘clumped’ than the overall mass distribution, and are poor tracers of the unseen mass even
on scales of several Mpc. Possible forms for the unseen mass are discussed; and feedback processes are outlined whereby galaxy
formation can be suppressed in underdense regions. 相似文献
18.
We have extend Stormer’s problem considering four magnetic dipoles in motion trying to justify the phenomena of extreme “orderlines”
such as the ones observed in the rings of Saturn; the aim is to account the strength of the Lorentz forces estimating that
the Lorentz field, co-acting with the gravity field of the planet, will limit the motion of all charged particles and small
size grains with surface charges inside a layer of about 200 m thickness as that which is observed in the rings of Saturn.
For this purpose our interest feast in the motion of charged particles with neglected mass where only electromagnetic forces
accounted in comparison to the weakness of the Newtonian fields. This study is particularly difficult because in the regions
we investigate these motions there is enormous three dimensional instability. Following the Poincare’s hypothesis that periodic
solutions are ‘dense’ in the set of all solutions in Hamiltonian systems we try to calculate many families of periodic solutions
and to study their stability. In this work we prove that in this environment charged particles can trace planar symmetric
periodic orbits. We discuss these orbits in details and we give their symplectic relations using the Hamiltonian formulation
which is related to the symplectic matrix. We apply numerical procedures to find families of these orbits and to study their
stability. Moreover we give the bifurcations of these families with families of planar asymmetric periodic orbits and families
of three dimensional symmetric periodic orbits. 相似文献
19.
Matthew R. Edwards 《Astrophysics and Space Science》2012,339(1):13-17
Due to the Hubble redshift, photon energy, chiefly in the form of CMBR photons, is currently disappearing from the universe
at the rate of nearly 1055 erg s−1. An ongoing problem in cosmology concerns the fate of this energy. In one interpretation it is irretrievably lost, i.e., energy is not conserved on the cosmic scale. Here we consider a different possibility which retains universal energy conservation.
Treating gravitational potential energy conventionally as ‘negative’, it has earlier been proposed that the Hubble shift flips
positive energy (photons) to negative energy (gravitons) and vice versa. The lost photon energy would thus be directed towards gravitation, making gravitational energy wells more negative. Conversely, within astrophysical bodies, the flipping of gravitons
to photons would give rise to a ‘Hubble luminosity’ of magnitude −UH
0, where U is the internal gravitational potential energy of the object. Preliminary evidence of such an energy release is presented
in bodies ranging from planets, white dwarfs and neutron stars to supermassive black holes and the visible universe. 相似文献
20.
We investigate the early phase of the 13 February 2009 coronal mass ejection (CME). Observations with the twin STEREO spacecraft
in quadrature allow us to compare for the first time in one and the same event the temporal evolution of coronal EUV dimmings,
observed simultaneously on-disk and above-the-limb. We find that these dimmings are synchronized and appear during the impulsive
acceleration phase of the CME, with the highest EUV intensity drop occurring a few minutes after the maximum CME acceleration.
During the propagation phase two confined, bipolar dimming regions, appearing near the footpoints of a pre-flare sigmoid structure,
show an apparent migration away from the site of the CME-associated flare. Additionally, they rotate around the ‘center’ of
the flare site, i.e., the configuration of the dimmings exhibits the same ‘sheared-to-potential’ evolution as the postflare loops. We conclude
that the motion pattern of the twin dimmings reflects not only the eruption of the flux rope, but also the ensuing stretching
of the overlying arcade. Finally, we find that: i) the global-scale dimmings, expanding from the source region of the eruption, propagate with a speed similar to that of the
leaving CME front; ii) the mass loss occurs mainly during the period of strongest CME acceleration. Two hours after the eruption Hinode/EIS observations show no substantial plasma outflow, originating from the ‘open’ field twin dimming regions. 相似文献