共查询到20条相似文献，搜索用时 31 毫秒
1.
Applications of laser-created dense e<Superscript>+</Superscript>e<Superscript>−</Superscript> pairs
We review the recent developments of laser pair creation in the laboratory and their potential applications to astrophysics
and other frontiers. Many astrophysical phenomena involving e+e− plasmas may be systematically investigated in the laboratory setting. We also discuss potential applications of dense positronium
gas. 相似文献
2.
A runaway binary star escaping in runaway from the multiple system Θ1 Ori C is studied. The radial velocities of both components are measured and radial velocity curves are constructed and solved
for them. The physical parameters and chemical compositions of the stars are determined. 相似文献
3.
D. V. Denissenko 《Astronomy Letters》2004,30(9):630-633
We computed the occultations of stars brighter than 15m by the largest trans-Neptunian objects (TNOs) for the next ten years. In our search, we used the following catalogs: Hipparcos; Tycho2 with the coordinates of 2838666 stars taken from UCAC2 (Herald 2003); and UCAC2 (Zacharias et al. 2003) with 16356096 stars between \(12\mathop .\limits^m 00\) and \(14\mathop .\limits^m 99\) north of ?45° declination. We predicted the occultations of stars by the seventeen largest numbered TNOs, the recently discovered 2004 DW, and four known binary Kuiper Belt objects. We selected 64 events at solar elongations of no less than 30°, including the extremely rare occultation of a \(6\mathop .\limits^m 5\) star by the double asteroid (66652) 1999 RZ253 on October 4, 2007. Observations of these events by all available means are extremely important, since they can provide unique information about the sizes of TNOs and improve our knowledge of their orbits dramatically. 相似文献
4.
É. A. Vitrichenko 《Astronomy Letters》2002,28(12):843-846
We measured the radial velocity of the star θ1 Ori D from IUE spectra and used published observations. Based on these data, we determined the period of its radial-velocity variations, P=20.2675±0.0010 days, constructed the phase radial-velocity curve, and solved it by least squares. The spectroscopic orbital elements were found to be the following: the epoch of periastron passage Ep=JD 2430826.6±0.1, the system's center-of-mass velocity /Gg=32.4±1.0 km s?1, K=14.3±1.5 km s?1, Ω=3.3±0.1 rad, e=0.68±0.09, a1 sin i = 3 × 1010 km, and f1 = 0.0025M⊙. Twice the period, P=40.528±0.002 days, is also consistent with the observations. 相似文献
5.
I. I. Romanyuk V. E. Panchuk N. E. Piskunov D. O. Kudryavtsev 《Astrophysical Bulletin》2007,62(1):26-35
The possibility of investigating the vertical structure of the magnetic field in chemically peculiar main-sequence stars is discussed. The nonuniform distribution of chemical elements over the surface complicates the problem substantially. The most efficient measurements are shown to be those of the longitudinal field components based on spectral lines with wavelengths longer and shorter than 3646 Å (shortward and longward of the Balmer jump), which form at different optical depths in the atmosphere. Various methodological problems are addressed that must be overcome in order to accomplish the task. The brightest magnetic star α 2 CVn is observed with the echelle spectrometer equipped with an Uppsala CCD chip. New observations corroborate our previous result: the longitudinal component of the magnetic field B e of the α 2 CVn star increases with depth by about 30% over the atmosphere thickness scale. 相似文献
6.
Radosław Rek 《Solar physics》2010,261(2):337-351
The Maunder Minimum was the time during the second part of the 17th century, nominally from 1645 to 1717 AD, when unusually
low numbers of sunspots were observed. On the basis of numerous recorded observations of auroras in the early 18th century,
the end of the Minimum could be regarded as around 1700, but details of sunspot observations by Jan Heweliusz (Heweliusz,
Machina Coelestis, 1679), John Flamsteed and Philippe de La Hire in 1684 allow us to interpret the Maunder Minimum as the period without a significant
cessation of activity. This Minimum was also recognized in 14C data from trees which grew during the second part of 17th century.
The variation in the production rate of radioactive carbon isotope 14C is due to modulation of the cosmic ray flux producing it by the changing level of solar activity and solar magnetic flux.
Stronger magnetic fields in the solar wind make it more difficult for cosmic rays to reach the Earth, causing a drop in the
production rate of 14C. However, more detailed analyses of 14C data indicate that the highest isotope abundances do not occur at the time of sunspot minima, as would be expected on the
basis of modulation of the cosmic ray flux by the solar magnetic field, but two years after the sunspot number maximum. This
time difference (or phase delay) can be accounted for if in fact there are both solar and non-solar cosmic ray contributions.
Solar flares could also contribute high-energy particles and produce 14C and are generally not most frequent at the time of the highest sunspot numbers in the cycle. 相似文献
7.
A. V. Glushkov 《Astronomy Letters》2003,29(3):142-152
We present the results of a harmonic analysis of and search for clusters in the arrival directions of cosmic rays with energies E0≥5×1016 eV and zenith angles ?≤53° detected at the Yakutsk extensive air shower (EAS) array from 1974 to 2002. We show that the phase of the first harmonic periodically varies greatly and takes on nonrandom values at a confidence level ≥4σ. These phases point to the Supergalactic plane (the Local supercluster of galaxies). 相似文献
8.
A correlation analysis is made of the spatial distribution of galaxies in the Coma, Bridge, and A1367 clusters, which form
the Coma supercluster. The scale of the clustering of galaxies and the variation in their density distribution with the main
parameters of the galaxies– luminosity, morphological type, and observed H I deficiency in the 21 cm line– are evaluated.
The mass-to-luminosity ratios are computed for the spiral galaxies in the Coma, Bridge, and A1367 clusters. It is suggested
that a larger fraction of hypothetical dark matter may be concentrated in the spiral galaxies which predominantly populate
the subclusters previously identified by us within these clusters than in the spiral galaxies observed in the peripheral regions
of the clusters. 相似文献
9.
S. L. Parnovsky 《Astronomy Letters》2008,34(7):451-456
We have obtained new constraints on the cosmological parameters Ω m and σ 8 from the peculiar velocities of flat edge-on spiral galaxies from the RFGC catalog. Based on these results presented graphically, we have found the quantitative condition (Ω m /0.3)0.37 σ 8 = 0.92 ± 0.05. The estimates of Ω m and σ 8, along with their combinations Ω m α σ 8 for various α, are compared with the estimates by other authors. 相似文献
10.
We consider the circular planar restricted three-body problem with the mass parameter μ = 5 × 10?5. Two families of periodic solutions are calculated: family c, starting from the collinear fixed point L 1, and the initial part of familyi, which begins by direct circular orbits of an infinitely small radius around the body of bigger mass. The calculated families are very close to the generating ones, which we described earlier. In particular, the existence of the predicted zigzag structure of characteristics of family iis verified. New properties of the planar and vertical traces are discovered. 相似文献
11.
Radosław Rek 《Solar physics》2010,267(2):361-375
Solar flares take place in regions of strong magnetic fields and are generally accepted to be the result of a resistive instability
leading to magnetic reconnection. When new flux emerges into a pre-existing active region it can act as a flare and coronal
mass ejection trigger. In this study we observed active region 10955 after the emergence of small-scale additional flux at
the magnetic inversion line. We found that flaring began when additional positive flux levels exceeded 1.38×1020 Mx (maxwell), approximately 7 h after the initial flux emergence. We focussed on the pre-flare activity of one B-class flare
that occurred on the following day. The earliest indication of activity was a rise in the non-thermal velocity one hour before
the flare. 40 min before flaring began, brightenings and pre-flare flows were observed along two loop systems in the corona,
involving the new flux and the pre-existing active region loops. We discuss the possibility that reconnection between the
new flux and pre-existing loops before the flare drives the flows by either generating slow mode magnetoacoustic waves or
a pressure gradient between the newly reconnected loops. The subsequent B-class flare originated from fast reconnection of
the same loop systems as the pre-flare flows. 相似文献
12.
Several strong but erroneous statements were made by R. Rek in an article published in this volume of Solar Physics. Here we show that these misleading statements are caused by neglecting the known effects of the carbon cycle and misinterpretation
of the data. In particular we show that the claim of the Maunder minimum being “the period without a significant cessation
of activity” contradicts the bulk of observational evidence and is caused by the misinterpretation of proxy data. 相似文献
13.
We study the radial-velocity and light curves of the two eclipsing binaries EE Aqr and Z Vul. Using the latest version of the Wilson and Van Hamme (Computing Binary Star Observables, 2003) model, absolute parameters for the systems are determined. We find that EE Aqr and Z Vul are near-contact and semi-detached systems, respectively. The primary component of EE Aqr fills about 96% of its ‘Roche lobe’, while its secondary one appears close to completely filling this limiting volume. In
a similar way, we find fill-out proportions of about 72 and 100% of these volumes for the primary and secondary components
of Z Vul respectively. We compare our results with those of previous authors. 相似文献
14.
In this paper we summarize and analyze the results of observation of linear polarization of H
α emission for solar flares and moustaches obtained earlier. Basic structural and evolutional properties of the observed polarization
are formulated and presented. A conclusion is drawn that polarization data obtained from rough time and spatial averaging
of Stokes parameters distort the true picture of polarization of H
α emission in flares and moustaches. 相似文献
15.
V. A. Simonenko D. A. Gryaznykh N. G. Karlykhanov V. A. Lykov A. N. Shushlebin 《Astronomy Letters》2007,33(2):80-92
We study the influence of turbulent mixing on the development of thermonuclear flashes in the surface layers of neutron stars. A simple K ε model that includes various physical processes is used to describe the turbulent processes. In contrast to the widespread mixing-length theory, the K ε model does not require using additional dimensional parameters, traces the development of turbulence in dynamics, describes the various turbulence development scenarios (gravitational and shear instabilities, convection, semiconvection, etc.) in a unified way, and can be used in multidimensional numerical simulations. Empirical constants of the model are chosen on the basis of experimental data and direct numerical simulations of typical processes. We have used the Era and Tigr-3T software packages to numerically simulate thermonuclear flashes in the accretion-renewable atmospheres of neutron stars. Turbulence is shown to accelerate significantly the transport of released energy to the stellar surface. Mixing equalizes the concentrations of matter components throughout the burning layer and increases the amount of matter involved in the thermonuclear burning during a flash. 相似文献
16.
Badam Singh Kushvah 《Astrophysics and Space Science》2011,333(1):49-59
This paper describes design of the trajectory and analysis of the stability of collinear point L
2 in the Sun-Earth system. The modified restricted three body problem with additional gravitational potential from the belt
is used as the model for the Sun-Earth system. The effect of radiation pressure of the Sun and oblate shape of the Earth are
considered. The point L
2 is asymptotically stable up to a specific value of time t correspond to each set of values of parameters and initial conditions. The results obtained from this study would be applicable
to locate a satellite, a telescope or a space station around the point L
2. 相似文献
17.
We present the results of our hydrodynamic calculations of radial pulsations in helium stars with masses 1 M⊙ ≤ M ≤ 10 M⊙, luminosity-to-mass ratios 1 × 103L⊙/M⊙ ≤ L/M ≤ 2 × 104L⊙/M⊙, and effective temperatures 2 × 104 K ≤ Teff ≤ 105 K for mass fractions of helium Y=0.98 and heavy elements Z=0.02. We show that the lower boundary of the pulsation-instability region corresponds to L/M ～ 103L⊙/M⊙ and that the instability region for L/M ? 5 × 103L⊙/M⊙ is bounded by effective temperatures Teff ? 3 × 104 K. As the luminosity rises, the instability boundary moves into the left part of the Hertzsprung-Russell diagram and radial pulsations can arise in stars with effective temperatures Teff ? 105 K at L/M ? 7 × 103L⊙/M⊙. The velocity amplitude for the outer boundary of the hydrodynamic model increases with L/M and lies within the range 200 ? ΔU ? 700 km s?1 for the models under consideration. The periodic shock waves that accompany radial pulsations cause a significant change of the gas-density distribution in the stellar atmosphere, which is described by a dynamic scale height comparable to the stellar radius. The dynamic instability boundary that corresponds to the separation of the outer stellar atmospheric layers at a superparabolic velocity is roughly determined by a luminosity-to-mass ratio L/M ～ 3 × 104L⊙/M⊙. 相似文献
18.
We have performed hydrodynamic calculations of the radial pulsations of helium stars with masses 10M⊙ ≤ M ≤ 50M⊙, luminosity-to-mass ratios 5 × 103L⊙/M⊙ ≤ L/M ≤ 2.5 × 104L⊙/M⊙, and effective temperatures 2 × 104 K ≤ Teff ≤ 105 K for helium and heavy-element mass fractions of Y=0.98 and Z=0.02, respectively. We show that the high-temperature boundary of the instability region for radial pulsations at L/M ? 104L⊙/M⊙ extends to Teff≈105 K. The amplitude of the velocity variations for outer layers is several hundred km s?1, while the brightness variations in the B band of the UBV photometric system are within the range from several hundredths to half a magnitude. At constant luminosity-to-mass ratio, the radial pulsation period is determined only by the effective temperature of the star. In the ranges of luminosity-to-mass ratios 104L⊙/M⊙ ≤ L/M ≤ 2 × 104L⊙/M⊙ and effective temperatures 5 × 104 K ≤ Teff ≤ 9 × 104 K, the periods of the radial modes are within 6 min ?Π?103 min. 相似文献
19.
A. R. El-Nabulsi 《Astrophysics and Space Science》2010,325(2):277-281
In this work, we explore many cosmological implications of a four-dimensional cosmology dominated by quintessence with a static
traversable wormhole, spatio-temporal varying G and by taking into account a decaying cosmological constant and a decaying graviton mass by means of an additional bimetric
tensor in Einstein’s field equations proposed by Visser in 1998. 相似文献
20.
Additional analysis of the behavior of the international sunspot number (R) series and the solar radio flux density (F10.7 cm) series during two long (250–500 days) and distinct episodes of persistent ≈13-day variations (Crane, Solar Phys. 1998, 253, 177) is reported. The conclusion is that while the center-to-limb behavior of R does not change between solar minimum and solar maximum, F10.7 cm exhibits significantly less limb brightening at solar maximum than at solar minimum. 相似文献