排序方式： 共有28条查询结果，搜索用时 15 毫秒
21.
V. A. Hagen-Thorn V. M. Larionov E. G. Larionova N. A. Kudryavtseva A. V. Tikhonov A. V. Hagen-Thorn A. A. Arkharov A. Di Paola F. D'Alessio 《Astronomy Letters》2004,30(4):209-217
We present the results of our multicolor observations of BL Lac in the period 1999–2001. We show that the spectral energy distribution of the variable component in the range from K to B had remained unchanged for three years. The power-law spectrum is indicative of its synchrotron nature. 相似文献
22.
Clark Tarasov Steele Coe Roche Shrader Buckley Larionov Larionova Lyuty Zaitseva Grunsfeld Fabregat & Parise 《Monthly notices of the Royal Astronomical Society》1998,294(1):165-176
The results of a 7-yr optical and UV spectroscopic study of the high-mass X-ray binary A 0535+26 are presented. It was found that throughout the period of the observations the line profile of Hα showed considerable variability. A correlation between the equivalent width of Hα and both V -band magnitude and ( B − V ) colour excess was observed, albeit with considerable scatter present in the data set. A giant X-ray flare in early 1994 was accompanied by a fading in optical and infrared photometric bands, and a reduction in the equivalent width of Hα. When the star was observed in 1994 September, it was found to have developed a double-peaked Hα profile, and further observations saw the V/R peak ratio vary cyclically, with a period of ∼1 yr. If this is identified as a global one-armed oscillation, it becomes the shortest period ever observed in a Be star. The accompanying photometric and spectroscopic observations provide a test of any theory seeking to describe the onset and behaviour of such a density wave. 相似文献
23.
L. S. Lyubimkov D. L. Lambert T. M. Rachkovskaya S. I. Rostopchin A. E. Tarasov D. B. Poklad V. M. Larionov L. V. Larionova 《Monthly notices of the Royal Astronomical Society》2000,316(1):19-32
High-resolution spectral observations of 123 B0–B5 stars in the main sequence evolutionary phase were obtained at two observatories, namely the McDonald Observatory (McDO) and the Crimean Astrophysical Observatory (CrAO). Accurate equivalent widths W of two Balmer lines, H β and H γ , and ten He i lines were obtained for all the stars, as well as of the He ii λ 4686 line for the hottest ones. A careful analysis of the measured equivalent widths was performed. It is shown that there is a very good agreement between the W values derived from the McDO and CrAO spectra for 14 common stars. A comparison with published data leads to the conclusion that the W values measured earlier by some authors for strong He i lines are very likely to be underestimated. Infrared photometric observations in the J , H , and K bands were performed for 70 programme stars. All these data will be used in other papers: in particular for the T eff and log g determination and for the He, C, N and O abundance analyses. 相似文献
24.
Tsvetkov D. Yu. Pavlyuk N. N. Vozyakova O. V. Shatsky N. I. Tatarnikov A. M. Nikiforova A. A. Baklanov P. V. Blinnikov S. I. Ushakova M. G. Larionova E. G. Borman G. A. 《Astronomy Letters》2021,47(5):291-306
Astronomy Letters - The results of UBVRIJHK photometry for the type II-P supernova SN 2018aoq in NGC 4151 obtained from April 4, 2018, to January 14, 2019, with several telescopes, including the... 相似文献
25.
The eastern margin of Sarmatia comprises the Paleoproterozoic (2.1–2.05 Ga) rock associations of the eastern Voronezh Crystalline Massif, including the Lipetsk-Losevo volcanic-plutonic belt and the adjacent East Voronezh lithotectonic zone composed of metasedimentary rocks of the Vorontsovka Group. The isotopic and geochemical study of the available drill cores that characterize the main rock associations of the Lipetsk-Losevo belt and its nearest framework allowed us to furnish evidence for the formation of this belt in the regime of an island arc at the active margin of the Archean continent above a low-angle subduction zone. The juvenile isotopic and geochemical signatures of metaturbidites of the Vorontsovka Group indicate that only a fast growing mountain edifice with the Lipetsk-Losevo Belt in its highest part (foreland) could have been a provenance of the flysch basin. It is proposed to name this Paleoproterozoic mountain system the East Sarmatian Orogen. The hinterland of this orogen embraced the megablock of the Kursk Magnetic Anomaly as a part of the Voronezh Massif and the Azov Block of the Ukrainian Shield. It has been shown that the East Sarmatian Orogen was formed in the same way as accretionary orogens of the Cordilleran type. 相似文献
26.
Evolution of Archean magmatism is one of the key problems concerning the early formation stages of the Earth crust and biosphere, because that evolution exactly controlled variable concentrations of chemical elements in the World Ocean, which are important for metabolism. Geochemical evolution of magmatism between 3.5 and 2.7 Ga is considered based on database characterizing volcanic and intrusive rock complexes of granite-greenstone terrains (GGT) studied most comprehensively in the Karelian (2.9–2.7 Ga) and Kaapvaal (3.5–2.9 Ga) cratons and in the Pilbara block (3.5–2.9 Ga). Trends of magmatic geochemical evolution in the mentioned GGTs were similar in general. At the early stage of their development, tholeiitic magmas were considerably enriched in chalcophile and siderophile elements Fe2O3, MgO, Cr, Ni, Co, V, Cu, and Zn. At the next stage, calc-alkaline volcanics of greenstone belts and syntectonic TTG granitoids were enriched in lithophile elements Rb, Cs, Ba, Th, U, Pb, Nb, La, Sr, Be and others. Elevated concentrations of both the “crustal” and “mantle-derived” elements represented a distinctive feature of predominantly intrusive rocks of granitoid composition, which were characteristic of the terminal stage of continental crust formation in the GGTs, because older silicic rocks and lithospheric mantle were jointly involved into processes of magma generation. On the other hand, the GGTs different in age reveal specific trends in geochemical evolution of rock associations close in composition and geological position. First, the geochemical cycle of GGT evolution was of a longer duration in the Paleoarchean than in the Meso-and Neoarchean. Second, the Paleoarche an tholeiitic associations had higher concentrations of LREE and HFSE (Zr, Ti, Th, Nb, Ta, Hf) than their Meso-and Neoarchean counterparts. Third, the Y and Yb concentrations in Paleoarchean calc-alkaline rock associations are systematically higher than in Neoarchean rocks of the same type, while their La/Yb ratios are in contrast lower than in the latter. These distinctions are likely caused by evolution of mantle magmatic reservoirs and by changes in formation mechanisms of silicic volcanics and TTG granitoids. The first of these factors was likely responsible for appearance of sanukitoid magmatic rocks in the Late Mesoarchean. Representative database considered in the work includes ca. 500 precision analyses of Archean magmatic rocks. 相似文献
27.
Yu. O. Larionova A. V. Samsonov K. N. Shatagin A. A. Nosova 《Geology of Ore Deposits》2013,55(5):320-340
The Rb-Sr age of metasomatic rocks from four gold deposits and occurrences localized in Archean granite-greenstone belts of the western, central, and southern Karelian Craton of the Baltic Shield has been determined. At the Pedrolampi deposit in central Karelia, the dated Au-bearing beresite and quartz-carbonate veins are located in the shear zone and replace Mesoarchean (～2.9 Ga) mafic and felsic metavolcanic rocks of the Koikar-Kobozero greenstone belt. At the Taloveis ore occurrence in the Kostomuksha greenstone belt of western Karelia, the dated beresite replaces Neoarchean (～2.7 Ga) granitoids and is conjugated with quartz veins in the shear zone. At the Faddeinkelja occurrence of southern Karelia, Aubearing beresite in the large tectonic zone, which transects Archean granite and Paleoproterozoic mafic dikes, has been studied. At the Hatunoja occurrence in the Jalonvaara greenstone belt of southwestern Karelia, the studied quartz veins and related gold mineralization are localized in Archean granitoids. The Rb-Sr isochrons based on whole-rock samples and minerals from ore-bearing and metasomatic wall rocks and veins yielded ～1.7 Ga for all studied objects. This age is interpreted as the time of development of ore-bearing tectonic zones and ore-forming hydrothermal metasomatic alteration. New isotopic data in combination with the results obtained by our precursors allow us to recognize the Paleoproterozoic stage of gold mineralization in the Karelian Craton. This stage was unrelated to the Archean crust formation in the Karelian Block and is a repercussion of the Paleoproterozoic (2.0–1.7 Ga) crust-forming tectonic cycle, which gave rise to the formation of the Svecofennian and Lapland-Kola foldbelts in the framework of the Karelain Craton. The oreforming capability of Paleoproterozoic tectonics in the Archean complexes of the Karelian Craton was probably not great, and its main role consisted in reworking of the Archean gold mineralization of various genetic types, including the inferred orogenic mesothermal gold concentrations. 相似文献
28.