Stellar associations and complexes in M33

About 460 OB associations were selected by a comparison of theUBV plates. TheUBV photographic photometry of 1944 blue stars in the associations was made. The new associations appear like cores within Humphreys and Sandage's associations. Their star content, size distribution, and mean size 80 pc confirm their identity with the OB associations in the Galaxy and in the Magellanic clouds. The boundaries of the associations are delineated mainly by the density of the resolved stars on theU plates. It is impossible to divide them into smaller areas. The genuine OB associations form groups of two or more members with a length scale of 250 pc. Their boundaries were delineated independently, but they coincide with the OB associations of Humphreys and Sandage (1980). These groups represent real concentration of blue massive stars with a large age dispersion. The star complexes unify a group of associations,Hii regions, andHi peak distribution. Their mean size is 570 pc. The extensiveHi clouds with a mean size of 1.2 kpc contain two or more star complexes. The questions related to star formation are briefly discussed.     

The luminosity of red supergiants in the andromeda galaxy

A blink survey of M31 undertaken by means ofB andV plates taken at the 2 m Rozhen observatory telescope gave the possibility to select ten brightest red supergiant candidates. There are a few bright red supergiants in M31 in comparison the LMC, M33, and our Galaxy. They are more frequent in the northern part of M31 where the higher rate of star formation occurs. Our search indicatedM _V –8.0 for the brightest red supergiants. Their occurrence in a galaxy depends not only on luminosity of the latter but also on the rate of star formation in it.     

U–Pb dating and composition of inclusions in zircon from ophiolitic gabbro of the Klyuchevsk massif (Middle Urals): Results and geological interpretation

The U–Pb (SHRIMP) dating of zircon from the layered complex of ophiolitic gabbro in the Klyuchevsk massif yielded an age of 456 ± 6 Ma corresponding within the limits of error to zircon dates obtained for other petrographic varieties from this massif. The investigation of the composition of silicate inclusions in dated zircon grains revealed that they are represented by typical metamorphic minerals: albite, zoisite, and secondary amphiboles. The data indicate that zircon was crystallized during metamorphic transformations of gabbroids and its U–Pb age (Late Ordovician–Silurian) is characteristic of all rocks in the ophiolite association of the Klyuchevsk massif indicating the age of metamorphism, not their formation time.     

Empirical phengite geobarometer: Background,calibration, and application

Phengite is a common metamorphic mineral stable in a wide pressure range. The dependence of pressure on silicon content established in the mid-20th century allowed us to propose a phengite-based geobarometer. Recently, the phengite geobarometer was calibrated by Caddik and Thompson (2008) but in the narrow pressure range. However, there attempts have been made to extend this range. We have analyzed the large number of published datasets on phengite composition. These data included both natural and experimental specimens of well defined P–T-conditions. For moderate temperatures (T < 750°C), two groups of phengite are identified. These groups are divided by silicon content value of 3.25 apfu. Different geobarometer equations were suggested for both groups. The precision of these geobarometers is ±0.34 GPa and ±0.56 GPa, respectively. There is no evidence of phengite used as a geobarometer at high temperatures (T > 750°C). The derived dependences were applied to study the conditions of gneiss and schist metamorphism of the Blyb metamorphic complex in the Northern Caucasus. This study shows that the peak pressure of gneiss and schist metamorphism is 2.0–2.2 ± 0.56 GPa. The latter agrees with previous data on the Blyb metamorphic complex.     

New carbonatite complex in the western Baikal area,southern Siberian craton: Mineralogy,age, geochemistry,and petrogenesis

A dike–vein complex of potassic type of alkalinity recently discovered in the Baikal ledge, western Baikal area, southern Siberian craton, includes calcite and dolomite–ankerite carbonatites, silicate-bearing carbonatite, phlogopite metapicrite, and phoscorite. The most reliable ⁴⁰Ar–³⁹Ar dating of the rocks on magnesioriebeckite from alkaline metasomatite at contact with carbonatite yields a statistically significant plateau age of 1017.4 ± 3.2 Ma. The carbonatite is characterized by elevated SiO₂ concentrations and is rich in K₂O (K₂O/Na₂O ratio is 21 on average for the calcite carbonatite and 2.5 for the dolomite–ankerite carbonatite), TiO₂, P₂O₅ (up to 9 wt %), REE (up to 3300 ppm), Nb (up to 400 ppm), Zr (up to 800 ppm), Fe, Cr, V, Ni, and Co at relatively low Sr concentrations. Both the metapicrite and the carbonatite are hundreds of times or even more enriched in Ta, Nb, K, and LREE relative to the mantle and are tens of times richer in Rb, Ba, Zr, Hf, and Ti. The high (Gd/Yb)_CN ratios of the metapicrite (4.5–11) and carbonatite (4.5–17) testify that their source contained residual garnet, and the high K₂O/Na₂O ratios of the metapicrite (9–15) and carbonatite suggest that the source also contained phlogopite. The Nd isotopic ratios of the carbonatite suggest that the mantle source of the carbonatite was mildly depleted and similar to an average OIB source. The carbonatites of various mineral composition are believed to be formed via the crystallization differentiation of ferrocarbonatite melt, which segregated from ultramafic alkaline melt.     

Climatic intrannual variability of the geostrophic circulation of the main Black Sea current

A quasi-periodic (wave) spatial-temporal structure of the intrannual variability of the climatic fields of the seawater geostrophic motion within the constant halocline in the Black Sea (75–300m) has been revealed on the basis of generalized archival data on hydrological observations in the main Black Sea current (MBSC) near the Crimea and Caucasus. The variability with annual and semi-annual periods has the character of standing quasi-geostrophic waves at 2- to 4-month periods which become progressive as the direction of their propagation changes during the year. The energy characteristics for the forms of variability revealed are discussed and interpreted from the viewpoint of gradient-eddy waves and the hydrodynamic instability of the MBSC.Translated by Mikhail M. Trufanov.     

Simulation of the Evolution of Wave Fields Induced by a Moving Cyclone over the Northwest Shelf of the Black Sea

The wave fields generated by cyclonic atmospheric disturbances in the region of the northwest shelf of the Black Sea are studied by using a σ-coordinate model. The problem is solved in the hydrostatic approximation with regard for nonlinearity and turbulent viscosity. To improve the space resolution of the model, we realize the procedure of embedded grids. It is shown that the action of a cyclone results in the formation of domains of pronounced surges whose shapes and location reflect the changes in the wind situation. The vertical structure of wave currents first depends only on the location of the atmospheric disturbance over the water area but, in the course time, begins to reflect specific features of the bottom topography.__________Translated from Morskoi Gidrofizicheskii Zhurnal, No. 1, pp. 42–54, January–February, 2005.     

黄河三角洲整体冲淤平衡及其地质意义

海岸侵蚀、三角洲面积减小已成为世界上关注的热点问题。三角洲造陆的趋势及速度制约着三角洲地区经济的持续发展和生态环境的演变。本文以1976、1986、、992、1996－1998年黄河三角洲卫星遥感照片及海区水深等实测资料为依据，通过其高潮线的对比分析，研究整个黄河三角洲面积变化的趋势。结果表明，黄河三角洲在整体淤进的同时伴随着蚀退，三角洲的造陆面积呈逐渐减小的趋势。通过对1950－1998年黄河利津站实测来水来沙资料的分析，发现近年来水沙呈递减趋势，这可能是三角洲造陆面积减小的重要原因。研究了黄河三角洲造陆面积与流域来水来沙的关系，从而得出当来沙量为2．45亿t/a时，三角洲面积整体趋于不冲不淤的平衡。若来水来沙量继续减少，黄河三角洲将走向全面蚀退，趋于消亡。     

Statistical estimates of the parameters of non-linear long internal waves off the South Crimea in the Black Sea

Hydrological data covering the South Crimea test area are used to calculate the mean profile of the variable Brunt-Väisälä frequency and the coefficients of the Korteweg-de Vries equation for internal waves at each station. Charts showing internal wave velocity isolines, non-linearity and dispersion parameters, and sea depth have been constructed. The average Brunt-Väisälä frequency profile has been used to calculate the Urcel parameter for internal waves, and non-linear properties of the internal waves observed have been assessed.Translated by Mikhail M. Trufanov.     

Long internal waves in the Tropical Atlantic ocean generated by periodic air pressure fluctuations

Taking into consideration stratification, the mean current velocity, and the tangential wind stress expressed in terms of air pressure fluctuations, we have derived iteration formulae and have performed computations of the amplitudinal characteristics of oceanic internal waves generated by air pressure waves of semi-diurnal and 4-day long periodicity propagating over the Tropical Atlantic Ocean. It has been demonstrated that such periodicity and wavelengths may contribute to the generation of long-amplitude internal waves, whose intensity is largely dependent on the direction of atmospheric wave propagation.Translated by Vladimir A. Puchkin.