Spatial–Temporal CO2 Variations near St. Petersburg Based on Satellite and Ground-Based Measurements

Izvestiya, Atmospheric and Oceanic Physics - The results of studying spatial–temporal CO2 variations near St. Petersburg in 2014–2017 based on satellite measurements (OCO-2 satellite)...     

Ferriplantites in the Bauxite-Bearing Lateritic Weathering Rocks (Futa Jallon-Mandingo Province,Africa): The Key Factors for Iron Accumulation

Doklady Earth Sciences - Investigation of the comprehensive geological material on the lateritic weathering rocks (Futa Jallon-Mandingo, Africa) led to original identification of a specific horizon...     

New Insights into the Geomorphological Evolution of the West African Relief

Doklady Earth Sciences - Detailed mapping and prospecting drilling for bauxites in the territory of the Fouta-Djallon Plateau and Mandingo Mountains and the compilation on the succession,...     

Time variability of the total methane content in the atmosphere over the vicinity of St. Petersburg

The results of measuring the methane content in the entire atmospheric thickness over the St. Petersburg region are given for 1991–2007. It is shown that, within this period, the mean annual cycle of the total methane content is characterized by its maximum values in December–January and its minimum values in June–August when the annual-cycle amplitude amounts to ∼3.6%. In this case, the annual variations in the total methane content may differ significantly from the mean annual cycle obtained in some years. A statistically significant linear trend of the total CH₄ content has not been revealed for 1991–2007. The obtained values of the linear-trend index have opposite signs in the winter and summer months (positive for January 0.6 ± 0.2%/year and February 0.4 ± 0.2%/year and negative for July 0.3 ± 0.2%/year and August 0.2 ± 0.1%/year). This fact suggests the tendency for an increase in the amplitude of the annual cycle of the total CH₄ content. The results of a spectral analysis of a series of data on the total CH₄ content show that, for 1991–2007, the following harmonics are pronounced with a confidence of 95%: 12 months (annual harmonic), 32 months (quasi-biennial oscillations), and 55 months (4.5 years), which are also pronounced in the series of meteorological parameters and total ozone content.     

Alluvium: Implications for stratigraphy and correlation of quaternary sediments

Based on a generalized knowledge of conditions and mechanisms for accumulation of the cycle terrace alluvium on plain and mountain rivers, alluvium is suggested as an instrument for stratigraphic studies, interregional correlation, and correction of present schemes. Diachronous alluvial formations are uniformly constructed. They include two subunits, a lower “warm” and an upper “cool” one. In addition the formations are subdivided in dynamic phases that display a dominating regime and stages of erosion-and-accumulation cycle. Alluvial formations are characterized by a peculiar mechanical and mineralogical composition, gradation, bedding, thickness, landscape and climatic conditions of accumulation, paleontological content, character of occurrence, and position in a cycle incision. All these characters of an alluvial formation and its subformations correspond to a complete climatic rhythm and oscillation stages. Alluvial formations are associated in a certain way with glacial and marine sediments making up a single formation complex.     

Modeling the Star Population of Resolved Galaxies

A program is developed for determining the history of star-forming galaxies based on the use of two- or multicolor photometry of the resolved stars in a given galaxy. We create a library of synthetic color-magnitude diagrams from theoretical stellar isochrones, taking the initial mass function, distance to the galaxy, internal and external absorption, and photometric errors into account. The resulting synthetic diagrams are combined linearly and compared quantitatively with photometric data for stars in a galaxy in order to determine star formation rates as a function of age and metallicity. This program is tested in detail under different conditions using artificial color-magnitude diagrams. Special attention is given to the limiting case when only the brightest stars of a galaxy can be seen in the color-magnitude diagram and the number of resolved stars is at most a few hundred. This limiting case corresponds to a large fraction of the nearby galaxies at distances of 3-5 Mpc observed by large ground based telescopes and the Hubble Space Telescope.     

The Unique Role of Pore Water in Lateritic Bauxite Formation,Republic of Guinea

Doklady Earth Sciences - Results of the hydrogeochemical study of bauxite-bearing lateritic mantles of the Futa Djallon‒Mandingo Province, West Africa, have allowed us to characterize for the...     

Photometry of young starlike objects in the dwarf galaxy NGC 2976— age and metallicity

We present BVI_c photometry of the brightest stars andcompact star clusters in NGC 2976, a dwarf galaxy in the interacting M81/M82 group. Deep CCD images of the galaxy were obtained with the 6m‐Telescope of the Special Astrophysical Observatory (Russia) at arcsec resolution. About 290 young stars and concentrated young clusters were measured. Supplementary data in the ultraviolet are taken from the literature. The extinction to the measured objects is comparatively low, E(B — V) ∼ 0.15 .. 0.20 mag. We estimate the ages of youngest resolved stars and concentrated star clusters to be ∼5 · 10⁶ years. This population is concentrated in a broad stripe facing M81. In the central disk the population is a bit older, about 8 · 10⁶ years, this may be a hint to an outward spreading star formation process. The metallicity of the disk population is estimatedas solar (z ∼ 0.02) from a fitting to Padova theoretical stellar isochrones.     

KDG218, a nearby ultra-diffuse galaxy

We present properties of the low-surface-brightness galaxy KDG218 observed with the HST/ACS. The galaxy has a half-light (effective) diameter of a _e = 47″ and a central surface brightness of SB _V (0) = 24.^m4/□″. The galaxy remains unresolved with the HST/ACS, which implies its distance of D > 13.1 Mpc and linear effective diameter of A _e > 3.0 kpc. We notice that KDG218 is most likely associated with a galaxy group around the massive lenticular NGC4958 galaxy at approximately 22 Mpc, or with the Virgo Southern Extension filament at approximately 16.5 Mpc. At these distances, the galaxy is classified as an ultra-diffuse galaxy (UDG) similar to those found in the Virgo, Fornax, and Coma clusters. We also present a sample of 15 UDG candidates in the Local Volume. These sample galaxies have the following mean parameters: 〈D〉 = 5.1 Mpc, 〈A _e 〉 = 4.8 kpc, and 〈SB _B (e)〉 = 27.^m4/□″. All the local UDG candidates reside near massive galaxies located in the regions with the mean stellar mass density (within 1 Mpc) about 50 times greater than the average cosmic density. The local fraction of UDGs does not exceed 1.5% of the Local Volume population. We notice that the presented sample of local UDGs is a heterogeneous one containing irregular, transition, and tidal types, as well as objects consisting of an old stellar population.