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1.
Heinrich Eichhorn 《Astronomische Nachrichten》1971,293(3):127-130
It is shown that there is no intrinsic difference between the so-called “astrometric” and “photogrammetric” methods of reducing star plates, and that either, when applied by competent investigators, will yield equivalent results. 相似文献
2.
Abstract— We have detected three unusual, low-relief circular features, 1.2 to 2.1 km in diameter, in the northwest Noachis highlands, which may be craters that have undergone isostatic deformation. They may shed light on the existence, nature, and timing of suspected widespread Martian erosion/obliteration events, and offer clues to a type of Martian terrain softening. In the surrounding area, we find an anomalous deficiency of craters in the 3–11 km diameter range and evidence that larger, older craters have undergone relief softening and infill. We discuss three different hypotheses to explain these features, two of which involve Martian ice. This region may have undergone a transient event in which a near-surface permafrost layer (several hundred meters deep) underwent partial melting or softening. This would allow relaxation of kilometer-scale craters and softening of larger craters. Crater data presented here suggest that this event happened some time in mid-Martian history. Whether the event was regional or related to global-scale events is uncertain, though it may represent a class of events that also happened in other Martian areas. 相似文献
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4.
A phenomenological model for V 361 Lyr is proposed. Probably it is a binary system which consists of a mass accreting primary star with mass of about M1 ≈ 0·81 M⊙ and radius R1 ≈ (6.1 ± 0·4) · 1010 cm and a mass losing secondary with about M2 ≈ 0·77 M⊙ and R2 ≈ 5.8 · 1010 cm. The secondary fills its Roche lobe, but the primary is something smaller than this lobe, contrary to the models of W UMa-type systems. So the hot spot appears in the atmosphere of the primary, but not in a disk, like in cataclysmic variables. The luminosity of the hot spot, L = (6-15) · 1032 erg/s, is large enough to be the main emission source of the system in visible light. So phenomenologically the object may be somewhat between W UMa-type stars and cataclysmic variables. 相似文献
5.
Nearly 15 years after the proposal of the superanoxia concept (Isozaki, Y., 1994. Superanoxia across the Permo–Triassic boundary: record in accreted deep-sea pelagic chert in Japan. In: Embry, A.F., Beauchamp, B., Glass, D.J. (Eds.), Pangea: Global Environments and Resources. Memoir, Canadian Society of Petroleum Geologists, 17, pp. 805–812.), it is an appropriate timing to re-evaluate its geological context with the updated dataset. Kakuwa (Kakuwa, Y., 2008. Evaluation of palaeo-oxygenation of the ocean bottom across the Permian–Triassic boundary. Global and Planetary Change 63, 40–56.) lately discussed that the deep-sea anoxia across the Permian–Triassic boundary (P–TB) may have been much shorter than previously proposed, on the basis of ichnofabrics and geochemical data; however, his interpretations of the data do not appear straightforward nor persuading, and thus his claim is likely misled. Here we raise comments to his explanation on the following four issues: 1) invalid application of ichnofabric indices for shallow sea sediments to deep-sea cherts, 2) misinterpretation of Ce anomaly as a redox indicator, 3) improper application of various redox sensitive trace elements, and 4) questionable interpretations of δ34S data of pyrites. 相似文献
6.
由于举办2010年世界杯,南非吸引了全球的目光,许多会议也不约而同地在此举办。南非总统祖马说,世界杯的举办成为南非经济腾飞的一个契机,而一个在他的后院举办的国际天文学家参加的会议,更是一个促进南非国家发展,充满幻想但非常实际的活动。 相似文献
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8.
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
9.
The results of investigations of the Hα and Hβ lines in the spectrum of the star HD 206267 are presented. Observations were carried out in 2011–2014 at the Cassegrain focus of the 2-m telescope of the Tusi Shamakhy Astrophysical Observatory of the National Academy of Sciences of Azerbaijan using an echelle spectrometer. The following features have been revealed for the first time: the moving discrete absorption components in the core of the Hα line from the red side to the violet, the stable emission in the violet wing of the Hα line, the antiphase variation of the radial velocities and equivalent widths of the Hα line, and the independence of the changes of the equivalent widths of the Hβ line from the phase of the orbital period. No spectral features according to which this star could be considered as a source of X-ray radiation have been found. 相似文献
10.
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
11.
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
12.
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
13.
The lateral distribution of cascade particles in extensive air showers from cosmic rays with energy E0 ? 1017 eV has been studied at the Yakutsk array by the ground scintillation detectors over the period of continuous observations 1977–2017. The experimental data are compared with those computed with various models for the development of extensive air showers from the CORSIKA software package. The best agreement between the theory and experiment is observed for the QGSjet-01-d model. In the energy range (1?20)× 1017 eV there is a change in the cosmic-raymass composition from 〈lnA〉 ≈ 2.5 to the proton one. 相似文献
14.
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
15.
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
16.
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
17.
We analyze the observations of a quiescent prominence acquired by the Téléscope Heliographique pour l’Étude du Magnetisme et des Instabilités Solaires (THEMIS) in the He?i 5876 Å (He?i D3) multiplet aiming to measure the spectral characteristics of the He?i D3 profiles and to find for them an adequate fitting model. The component characteristics of the He?i D3 Stokes I profiles are measured by the fitting system by approximating them with a double Gaussian. This model yields an He?i D3 component peak intensity ratio of \(5.5\pm0.4\), which differs from the value of 8 expected in the optically thin limit. Most of the measured Doppler velocities lie in the interval ±?5 km?s?1, with a standard deviation of ±?1.7 km?s?1 around the peak value of 0.4 km?s?1. The wide distribution of the full-width at half maximum has two maxima at 0.25 Å and 0.30 Å for the He?i D3 blue component and two maxima at 0.22 Å and 0.31 Å for the red component. The width ratio of the components is \(1.04\pm0.18\). We show that the double-Gaussian model systematically underestimates the blue wing intensities. To solve this problem, we invoke a two-temperature multi-Gaussian model, consisting of two double-Gaussians, which provides a better representation of He?i D3 that is free of the wing intensity deficit. This model suggests temperatures of 11.5 kK and 91 kK, respectively, for the cool and the hot component of the target prominence. The cool and hot components of a typical He?i D3 profile have component peak intensity ratios of 6.6 and 8, implying a prominence geometrical width of 17 Mm and an optical thickness of 0.3 for the cool component, while the optical thickness of the hot component is negligible. These prominence parameters seem to be realistic, suggesting the physical adequacy of the multi-Gaussian model with important implications for interpreting He?i D3 spectropolarimetry by current inversion codes. 相似文献
18.
We estimate the electron density, \(n_{\mathrm{e}}\), and its spatial variation in quiescent prominences from the observed emission ratio of the resonance lines Na?i?5890 Å (D2) and Sr?ii?4078 Å. For a bright prominence (\(\tau_{\alpha}\approx25\)) we obtain a mean \(n_{\mathrm{e}}\approx2\times10^{10}~\mbox{cm}^{-3}\); for a faint one (\(\tau _{\alpha }\approx4\)) \(n_{\mathrm{e}}\approx4\times10^{10}~\mbox{cm}^{-3}\) on two consecutive days with moderate internal fluctuation and no systematic variation with height above the solar limb. The thermal and non-thermal contributions to the line broadening, \(T_{\mathrm{kin}}\) and \(V_{\mathrm{nth}}\), required to deduce \(n_{\mathrm{e}}\) from the emission ratio Na?i/Sr?ii cannot be unambiguously determined from observed widths of lines from atoms of different mass. The reduced widths, \(\Delta\lambda_{\mathrm{D}}/\lambda_{0}\), of Sr?ii?4078 Å show an excess over those from Na?D2 and \(\mbox{H}\delta\,4101\) Å, assuming the same \(T_{\mathrm{kin}}\) and \(V_{\mathrm{nth}}\). We attribute this excess broadening to higher non-thermal broadening induced by interaction of ions with the prominence magnetic field. This is suggested by the finding of higher macro-shifts of Sr?ii?4078 Å as compared to those from Na?D2. 相似文献
19.
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
20.
ITU 无线电通信议事全会考虑到a.用通信卫星双向交换时间信号有很大的潜力提高(时间)准确度和稳定度;b.实验结果表明其短期时间稳定度与理论估计相符;c.目前尚未取得关于长期稳定度研究的充分足够的经验; 相似文献