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Srinivas N. Mohan 《Icarus》1979,40(2):317-330
The global distribution of existing lunar topography suffers from a lack of measurements of far-side radii because of the sparsity of data types in the nonequatorial regions. This paper presents determinations of far-side lunar radii based on the reduction of photogrammetric measurements derived from selected Apollo 16 trans-Earth phase photographs. The regions covered in this analysis lie west of Mare Moscoviense between longitudes 90 and 130°E and latitudes 10 and 60°N. The determinations are made using control points appearing on both NASA topographic orthophoto maps and the Apollo 16 photographs. The estimated lunar radii are referred to these control points and determined with a relative accuracy of 500 m. The new lunar radii are used to generate a topographic map covering the area investigated. The map shows that, with the given spatial density of surface festures measured, basin-sized features can be resolved. In particular, the far-side craters Fabry, Riemann, and Szilard comprise a topographically depressed region about 500 km in diameter centered at 120°E and 38.5°N. The floor of this basin is 2.4 to 3.4 km below the reference sphere of 1738.0 km and 4.8 to 5.8 km below the northern rim of the basin. A comparison of the depth of the unfilled basin with the depths of maria-filled front-side basins leads to the conclusion that basalt fill of the near-side maria may be 2 km deep. The topographic map shows good correlation with geologic provinces of young plains and cratered terra in the far-side highland region investigated. Lack of correlation between sampled values of the state-of-the-art 16th-order and 16th-degree harmonic gravity field model and corresponding topographical values leads to the conclusion that the far-side region investigated is isostatically compensated. 相似文献
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Zdenek Sekanina 《Icarus》1978,33(2):415-427
A model is proposed for single close encounters between two small masses, m1and m2, which orbit a much larger mass, M. The main new feature of the model is the assumption of conic motion of the center of mass of m1and m2 in the gravitational field of M. Comparisons of the model with the three-body equations of motion indicate that the model is a useful approximation for m1, m2 ? 10?5M. The model is therefore applicable for encounters between bodies of the order of an earth mass or smaller in the presence of the sun. Comparisons are also made of outcomes obtained by the model with outcomes of numerical integration for a large variety of close encounters. The above comparisons reveal that for many purposes the model is an adequate approximation for those encounters with ? ≥ 4, where ? is the eccentricity of the hyperbolic orbit of m1about m2. 相似文献
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《天文和天体物理学研究(英文版)》2015,(8)
In this work, we report new quasars discovered in fields in the vicinity of the Andromeda(M31) and Triangulum(M33) galaxies with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST, also called the Guo Shou Jing Telescope) during the 2013 observational season, the second year of the regular survey. In total, 1330 new quasars are discovered in an area of ～133 deg2 around M31and M33. With i magnitudes ranging from 14.79 to 20.0 and redshifts from 0.08 to4.85, the 1330 new quasars represent a significant increase in the number of identified quasars in fields in the vicinity of M31 and M33. Up to now, there have been a total of 1870 quasars discovered by LAMOST in this area. The much enlarged sample of known quasars in this area can potentially be utilized to construct a precise astrometric reference frame for the measurement of minute proper motions of M31, M33 and their associated substructures, which are vital for understanding the formation and evolution of M31, M33 and the Local Group of galaxies. Moreover, in the sample,there are a total of 45, 98 and 225 quasars with i magnitudes brighter than 17.0, 17.5and 18.0 respectively. In the aforementioned brightness bins, 15, 35 and 84 quasars are reported here for the first time, and 6, 21 and 81 are reported in our pervious work. In addition, 0, 1 and 6 are from the Sloan Digital Sky Survey and 24, 41 and 54 are from the NED database. These bright quasars provide an invaluable sample to study the kinematics and chemistry of the interstellar/intergalactic medium of the Local Group. 相似文献
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D.R. Bates 《Planetary and Space Science》1974,22(8):1268
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Properties of dispersive Alfvén waves: 1. Kinetics (very low, intermediate, and low density plasmas)
P. P. Malovichko 《Kinematics and Physics of Celestial Bodies》2013,29(6):269-284
The work is devoted to the study of the behavior of dispersive Alfvén waves, including inertial and kinetic Alfvén waves, in astrophysical plasma of very low, intermediate, and low pressure. New and full solutions were obtained. The solutions for “ordinary” and inertial Alfvén waves were shown to be particular cases of the general solution. The effect of the parameters of the astrophysical medium on the behavior and properties of dispersive Alfvén waves was analyzed. All the main wave characteristics were obtained, namely, the dispersion, fading, polarization, density perturbations, and charge density perturbations, whose consideration is essential for observation and detection of these waves and for more adequate understanding of their role in different astrophysical processes that occur in the space environment. 相似文献
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D. K. Nadyozhin 《Astrophysics and Space Science》1977,51(2):283-301
The collapse of iron-oxygen stars with masses of 2M
has been calculated. The commencement of the collapse is due to dissociation of iron-group nuclei into free nucleons. After a while, the collapse proceeds in consequence of intensive energy losses due to neutrino volume radiation. At an intermediate stage of the collapse, the core — opaque with respect to neutrino radiation (neutrino core) — is formed inside the collapsing star. Both the gradual increase of the mass of the neutrino core and the partial absorption of neutrinos radiated from the surface of the neutrino core by the stellar envelope (deposition) were taken into account in our calculations. The kinetics of oxygen burning in the outer layers of the envelope was also allowed for. Neither the deposition, nor the oxygen burning, result in ejection of stellar envelopes. 相似文献
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M. K. Kuznetsov Ya. V. Pavlenko M. K. Galvez-Ortiz 《Kinematics and Physics of Celestial Bodies》2012,28(6):280-287
Spectral types (M4–M6), effective temperatures T ef (2700–2900 K), and free fall accelerations logg (4.0–4.5) are determined for five M dwarfs using their energy distributions in the spectral range λλ = 680…840 nm. Stellar spectra with resolutions R = 4000 were obtained using the IMACS spectrograph mounted on the ESO Walter Baade 6.5-m telescope. The spectral types are derived from spectral indices and the effective temperatures of the stars are estimated based on their spectral types. Values of T ef and logg are also derived from the comparison between the observed and theoretical energy distributions, calculated both for dust-free, standard NextGen model atmospheres of red dwarfs, and for semiempirical models considering the presence of dust in stellar atmospheres according to the technique developed by Pavlenko et al. We determine dust parameters for stellar atmospheres of these stars, and establish that it is necessary to account for the decrease in concentration of TiO molecules due to their condensation on dust grains, when T ef < 3000 K. We conclude that the radiation scattering by dust grains does not have an appreciable effect on energy distributions in the spectra of the considered stars. 相似文献
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Abstract— We discuss possible evidence for a dilution of 14C caused by the Tunguska impact event, proposed by Rasmussen et al. (1999). The results presented in that paper and other available information do not support this hypothesis. 相似文献
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Solar flare observations have been performed with the multichannel L.P.S.P. experiment on board OSO-8 NASA Satellite. Simultaneous H and K Caii, h and k Mgii, L and L Hi profiles have been recorded on the plage just before the flare, during the flare onset and relaxation phases. The different behaviour of line profiles and intensities during the flare is evidenced and indicates a downward propagation with relaxation times increasing from the upper part to the lower part of the chromosphere related to line formation processes. Using the H observed profile, an upper limit of 8 × 1013 cm-3 is derived for the electron density. 相似文献