排序方式： 共有34条查询结果，搜索用时 234 毫秒
21.
D. A. Kovaleva 《Astronomy Reports》2002,46(3):233-245
Evolutionary computations for intermediate-mass stars are analyzed using observed parameters for eclipsing SB2 binaries and theoretical parameters based on evolutionary tracks. Modern observations cannot be used to distinguish between models with and without convective overshooting for stars in the vicinity of the main sequence. Statistically significant discrepancies between the observed and computed stellar parameters are associated with systematic errors in photometric effective temperatures. After taking into account systematic effects, the theoretical computations fit the observational data uniformly well throughout the entire mass interval studied. Empirical and semiempirical (i.e., reduced to the ZAMS and with solar elemental abundances) formulas for the mass-luminosity, mass-effective temperature, and mass-radius relations are proposed. 相似文献
22.
The Binary star DataBase(BDB, http://bdb.inasan.ru) combines data from catalogs of binary and multiple stars of all observational types. There is a number of ways for variable stars to form or to be a part of binary or multiple systems. We describe how such stars are represented in the database. 相似文献
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24.
F. D. Fourie M. S. Huber E. Kovaleva M. D. Clark 《Meteoritics & planetary science》2023,58(9):1345-1364
Recent observations and geophysical studies at the Vredefort impact structure have indicated that the impact melt dikes in the central uplift of the structure have small depth extents. In this study, we performed magnetic and electrical resistivity tomography (ERT) surveys of the Lesutoskraal granophyre dike (LGD) and trenched to confirm its depth extent. The ERT survey showed that outcrops of the LGD are associated with shallow resistive zones with <3 m depth extent, but such zones do not occur where outcrops are absent. Visual observations in the trench confirmed that the dike has a small depth extent (~0.75 m) at this location. However, the magnetic survey revealed anomalies along the entire strike of the dike, even where no outcrops occur. We suggest that remagnetization of the host rock within a metamorphic contact aureole could explain the presence of magnetic anomalies in the absence of outcrops. Considering the results of the ERT survey, the observations made in the trench, and the surface distribution of outcrops of the LGD, we confirm that this dike has a small depth extent (<3 m) along its entire length and propose that outcrops represent the intersection of the dike terminus with the current erosional surface. 相似文献
25.
The stratigraphic division and sequence of the Upper Cretaceous sediments in eastern Heilongjiang Province,China,have been ambiguous and controversial,mainly due to a lack of biostratigraphically useful fossils and related radiometric dating.A new species of angiospermous fossil plant.Platanus heilongjiangensis sp.nov.,from Qitaihe in eastern Heilongjiang has been found in sediments conformably above which zircons from a rhyolitic tuff has been dated by U-Pb radiometric methods as 96.2± 1.7 Ma.indicating that the Upper Houshigou Formation is of Cenomanian age.This discovery not only provides new data to improve our stratigraphic understanding of the Houshigou Formation,but also shows that Platanus flourished in the early Late Cretaceous floras of the region.This new study also indicates active volcanism taking place in the eastern Heilongjiang region during the Cenomanian of the Late Cretaceous. 相似文献
26.
Analysis is presented of many-year spectrometric data in the visible band of electromagnetic spectrum collected for the Don R., including the Tsimlyansk Reservoir in 2010–2013 with a period of ~15 days. An algorithm has been proposed for separating spectral brightness coefficient of the rising radiation from water into six categories. A nomenclature scale of the trophic status of water bodies has been constructed. The obtained scale coincides with the nomenclature scales constructed by chlorophyll a concentration for water bodies under different physiographic conditions. The unquestioning advantage of remote sensing methods for assessing water body (WB) trophic status is emphasized, i.e., the possibility to carry out real-time studies within minutes at high representativeness of the results with respect to the examined aquatic ecosystem. 相似文献
27.
Astronomy Reports - We describe a homogeneous catalog compilation of common proper motion stars based on Gaia DR2. A preliminary list of all pairs of stars within the radius of 100 pc around the... 相似文献
28.
G. G. Matishov K. V. Dyuzhova G. V. Kovaleva V. V. Pol’shin 《Doklady Earth Sciences》2016,467(2):371-375
Applying the methods of absolute geochronology and lithology, it has been established that the average sedimentation rate in the Sea of Azov over the last 6000 years (Ancient and New Azov times) varied from 0.2 to 2.0 mm/year. Its minimum values are confined to transit and sediment-starved zones coinciding with the directions of the main marine currents. It has been indicated that changes in the water level of the Sea of Azov occur with lag relative to landscape–climate phases. The obtained data confirm the relation between marine and terrestrial processes occurring in the Sea of Azov region: transgressive phases are preceded by general humidification in adjacent regions, while regressive phases correlate with climate aridization. The biostratigraphic analysis of the Holocene sections examined reveals the unstable behavior of the sea level during their formation. The results of diatom analysis confirm development of the Phanagoria and Korsun Regressions and Nymphea Transgression. Frequent fluctuations of the Sea of Azov the level determined the rhythmical structure of the sedimentary sequence saturated with autochthonous and allochthonous organic matter. 相似文献
29.
G. G. Matishov G. V. Kovaleva Kh. A. Arslanov K. V. Dyuzhova V. V. Polshin A. E. Zolotareva 《Doklady Earth Sciences》2018,479(2):452-455
New data on the absolute age of Quaternary bottom deposits from the Sea of Azov based on the results of radiocarbon analysis (14C) are presented. Overall, 67 radiocarbon dating of bottom deposits of New and Ancient Azov Ages were obtained. The thickness of sediments of the New Azov Age and their distribution over different areas of the Sea of Azov was determined during the study; the results obtained were compared with the reference data available. An integrated approach to the study of deposits, based on the combination of the biostratigraphy methods and the results of absolute age dating, was applied. 相似文献
30.
D. A. Kovaleva 《Astronomy Reports》2001,45(12):972-983
We estimate the ages and metallicities for the components of 43 binary systems using a compilation of accurate observational data on eclipsing binaries for which lines of both components are visible in their spectra, together with two independent modern sets of stellar evolution models computed for a wide range of masses and chemical abundances. The uncertainties of the resulting values are computed, and their stability is demonstrated. The ages and metallicity are compared with those derived in other studies using different methods, as well as with independent estimates from photometric observations and observations of clusters. These comparisons con firm the reliability of our age estimates. The resulting metallicities depend significantly on the choice of theoretical model. Comparison with independent estimates favors the estimates based on the evolutionary tracks of the Geneva group. 相似文献