FG Sge at the stage of dust shell ejection

New photometric observations of the variable star FG Sge, a rapidly evolving planetary nebula nucleus, were performed in 2003–2008. On 230 nights, we obtained 86 UBV and 155 BV RI (or R _c , I _c ) magnitude estimates. The maximum amplitude of the V-band light variations was >8 ^m . Six deep minima and four high maxima were observed. Analysis of the light curve has shown that the pulsation period of the star remained constant since 1991 and was P = 115 days. We have studied the wavelength dependence of the extinction at various phases of the light curve. The blueing of the B-V color at deep minima is interpreted as the result of light scattering in the circumstellar dust shell of the star formed by preceding dust ejections since 1992. Our spectroscopic observations performed on nine nights in 2003–2007 with the 125-cm telescope at the Crimean Station of the Sternberg Institute have confirmed the previously detected intensity variations of the Swan bands and the sodium doublet with brightness. It is noted that the Swan bands originate in the upper atmosphere, the star’s extended envelope, while the sodium doublet originates mainly in the circumstellar shell of FG Sge. We suggest that the star is currently located in the temperature-luminosity diagram at the turning point of the horizontal track of cooling in the direction of hot stars—evolution caused by the last helium shell flash at the planetary nebula stage.     

Photometric variability and evolutionary status of the supergiant with an infrared excess HD 179821=V1427 aquilae

We present new results of our UBV photometry for HD 179821=V1427 Aql, an F supergiant with an infrared excess, from 2000 to 2008. The semiregular low-amplitude (ΔV = 0_. ^m 05−0_. ^m 20) photometric variability of the star with a cycle period from 130 to 200 days is caused by pulsations, along with the instability of a variable stellar wind. V1427 Aql also exhibits a long-term trend in the brightness and colors that is probably attributable to a change in the stellar temperature as a result of mass loss episodes, which cause variations in the continuum formation level. We present the results of our JHKLM photometry for V1427 Aql in 1992–2008. We trace the trend in the near-infrared brightness, which agrees with the long-term variability in the V band. Based on broadband photometry, we have determined the color excess for V1427 Aql: E(B−V) = 0.7. Based on low-resolution spectroscopy, we have estimated the stellar temperature and revealed variability of the Hα line caused by a change in the contribution from the emission component. The hypotheses of whether the star belongs to post-AGB objects or to massive yellow hypergiants are discussed.     

The role of forcing and internal dynamics in explaining the “Medieval Climate Anomaly”

Proxy reconstructions suggest that peak global temperature during the past warm interval known as the Medieval Climate Anomaly (MCA, roughly 950–1250 AD) has been exceeded only during the most recent decades. To better understand the origin of this warm period, we use model simulations constrained by data assimilation establishing the spatial pattern of temperature changes that is most consistent with forcing estimates, model physics and the empirical information contained in paleoclimate proxy records. These numerical experiments demonstrate that the reconstructed spatial temperature pattern of the MCA can be explained by a simple thermodynamical response of the climate system to relatively weak changes in radiative forcing combined with a modification of the atmospheric circulation, displaying some similarities with the positive phase of the so-called Arctic Oscillation, and with northward shifts in the position of the Gulf Stream and Kuroshio currents. The mechanisms underlying the MCA are thus quite different from anthropogenic mechanisms responsible for modern global warming.     

Expansion of oil and gas production and increase of environmental risk

Onshore oil and gas production is often accompanied by accidents of varying severities and negative consequences. Operations within the areas of peripheral seas and the World Ocean have significantly aggravated the situation and driven a significant part of the emergencies related to the production of hydrocarbons to regional and global levels. The use of new technologies in the production of shale hydrocarbons has added a new problem, that is, the probability of total contamination of a large volume of geological environment with highly toxic chemicals. The discovery of a new promising fossil energy source, gas hydrates, makes it possible only to outline the possible related hazards and shows that the environmental risk can increase by many times. To withstand the threat of emergencies related to the growth of hydrocarbon production, it is advisable to establish special control and rapid-response structures on a nationwide scale. Such structures may be open to international cooperation in the jurisdiction of the United Nations, if necessary.     

The candidate protoplanetary object IRAS 22223+4327 is a pulsating variable star

We present our photoelectric U BV observations of the candidate protoplanetary object IRAS 22223+4327 during four visibility seasons. The star exhibited periodic brightness variations with the maximum amplitudes \(\Delta U = 0\mathop .\limits^m 23, \Delta B = 0\mathop .\limits^m 18, and \Delta V = 0\mathop .\limits^m 12\) and a time scale of about 90 days, which is equal to the period derived by other authors from radial velocities. During these brightness variations, a correlation is observed between the (B-V) color index and brightness, which is characteristic of pulsations. We estimated the star’s spectral type from our photometric data to be F8 I. We detected a “deficit” of light in the U band. The star’s mean brightness and its spectral type appear to have not changed in the past half a century.     

Estimate of the Eutrophication Process in the Gruža Reservoir (Serbia and Montenegro)

The Gru?a Reservoir (located at 238…269 m a. s. l., volume 64.6 · 10⁶ m³, surface 934 ha, drainage area 318 km², max. depth 31 m, mean theoretical retention time 22 months) was investigated during the years 1996 to 2001. The obtained values of trophic state parameters (9…200 μg L^?1 total phosphorus, 3…99 μg L^?1 chlorophyll‐a, and 0.5…2 m transparency) indicate that water of the Gru?a Reservoir is eutrophic according to three types of classification: Carlson, OECD, and Jones and Lee. It was noticed that values of average biomass abundance are large in the Gru?a Reservoir, and they could indicate a richer trophic state. When these indices are cited in connection with parameters of the trophic state, it is apparent that the Gru?a Reservoir can be classified as a eutrophic water on the basis of total phosphorus content of chlorophyll‐a and hypertrophic water with respect to transparency.     

Current status of models with hot and cold dark matter

An analysis of a five-parameter family of cosmological models in a spatially flat Friedmann Universe with a zero Λ term is presented. The five parameters are (1) σ₈, the dispersion of the mass fluctuations in a sphere with radius 8h ^?1 Mpc, where h=H ₀/100 km s^?1 Mpc^?1 and H ₀ is the Hubble constant; (2) n, the slope of the density-perturbation spectrum; (3) Ω_v, the normalized energy density of hot dark matter; (4) Ω_b, the baryon density; and (5) h, the normalized Hubble constant. The density of cold dark matter is determined from the condition Ω _cdm >1?Ω_v?Ω _b . Analysis of the models is based on comparison of computational results with observational data for: (1) the number density and mass function of galaxy clusters (a so-called Press-Schechter formalism) and (2) the cosmic microwave background anisotropy. The first method enabled us to determine the value σ₈=0.52±0.01 with high accuracy. Using the resulting normalization of the density-perturbation spectrum, we calculated a model for the anisotropy of the cosmic microwave background radiation on large scales (l?10, where l is the harmonic number) and the required contribution of cosmological gravitational waves, characterized by the parameter T/S. The restrictions on T/S become weaker as Ω_v increases. Nevertheless, even when Ω_v≤0.4, models with h+n≥1.5 require a considerable contribution from gravitational waves: T/S?0.3. On the other hand, in models with Ω_v≤0.4 and a scale-invariant density-perturbation spectrum (n=1), we find T/S ?10(h?0.47). The minimization of T/S is possible only for the family of models with red spectra (n<1) and small h (<0.6). The value of Ω_v is determined most accurately by the data onΔT/T near the first acoustic peak (l?200). By imposing a general restriction on the amplitude of gravitational waves T/S∈[0, 3] and taking into account the available observational data on the amplitude of the acoustic peak of Sakharov oscillations, ranges of possible values n and Ω_v are derived. If the baryon number is constrained by nucleosynthesis data, the models under consideration can have both moderately red and blue power spectra n∈[0.9, 1.2] with a rather high concentration of hot particles Ω_v∈[0.2,0.4]. The conditions that n<0.9 and/or Ω_v<0.2 decrease the relative amplitude of the acoustic peak by over 30% compared to its value in the standard cold-dark-matter (CDM) model normalized using COBE data.     

Morphoscopy and morphometry of quartz grains from loess and buried soil layers

A complex method is suggested for the study of surfaces of sand grains. With this method, middle- and late Pleistocene loess-palaeosol sequences of the Russian Plain, Dnieper Basin, were studied. Surface texture of grains pointed to a dry and cold climate for their formation. During deposition of loess layers predominantly aeolian and cryogenic processes formed the grain surfaces. During interglacial and interstadial periods chemical weathering dominated.     

Relationships between Quantitative Parameters of Lake Areas and Khasyrei Areas on Thermokarst Plains with Fluvial Erosion

Doklady Earth Sciences - The purpose of this study was to identify relationships between the quantitative parameters of lake areas and khasyrei areas on erosion thermokarst plains. According to the...     

Euxinia as a dominant process during OAE1a (Early Aptian) on the Eastern Russian Platform and during OAE1b (Early Albian) in the Middle Caspian

A detailed study of the mineral composition and microstructure of the black shales associated with OAE1a (Eastern Russian Platform), OAE1b (Middle Caspian), and the host rocks has been carried out using X-ray diffraction, scanning electron microscopic, and microprobe analyses. The results provide important constraints for depositional environments in the sedimentary basins. Black shales with pyrite framboids imply euxinic (sulfidic) conditions with increased organic matter preservation. Disintegrating framboids suggest partial or complete dissolution of the organic matter inside the framboids due to increasing water oxygenation. OAE1a on the Eastern Russian Platform is heterogeneous as it includes thin interbeds of concretionary coccolith limestones within the interval of bituminous shales, and correlates with the Lower Aptian Rhagodiscus angustus nannofossil zone. The coccolith limestones indicate short intermittent episodes of interrupted stagnation, rapid oxygenation, and restoration of normal marine conditions. The presence of montmorillonite, albite, microcline, and diopside in the bituminous siltstones and in the host siltstones of OAE1a on the Eastern Russian Platform, as well as a high content of titanium in the black siltstones correlated with OAE1b in the Middle Caspian allow proposing significant input of pyroclastic material into the extant sea.