Associations of Dwarf Galaxies

Hubble Space Telescope Advanced Cameras for Surveys has been used to determine accurate distances for 20 galaxies from measurements of the luminosity of the brightest red giant branch stars. Five associations of dwarf galaxies that had originally been identified based on strong correlations on the plane of the sky and in velocity are shown to be equally well correlated in distance. Two more associations with similar properties have been discovered. Another association is identified that is suggested to be unbound through tidal disruption. The associations have the spatial and kinematic properties expected of bound structures with 1 - 10 x 10^11 solar mass. However, these entities have little light with the consequence that mass-to-light ratios are in the range 100 - 1000 in solar units. Within a well surveyed volume extending to 3 Mpc, all but one known galaxy lies within one of the groups or associations that have been identified.Comment: 50 pages, 2 tables, 15 encapsulated figures, 1 (3 part) jpg figure. Submitted to Astronomical Journa

CONDITION OF THE ERYTHROID PART OF BLOOD SYSTEM AT STRESSED ANIMALS WITH HYPOTHYREOSIS

Hypothyreosis, caused by introduction of mercazolil, leads to reduction of production of thyroid hormones, destabilization of membranes and. acceleration of erythrocytes destruction, activation of erythropoiesis, development of macroerythrocytosis in blood. In 28 days after cancelling of mercazolil reserves of red bone marrow are exhausted, in blood microerythrocytosis accrues. The stress in animals with hypothyreosis does not change the composition of blood erythrocytes and activity of erythrocytopoiesis, but promotes preservation of a marrowy reserve of erythrocytes and increases a level of thyroid hormones

The approach of the transport & logistics cluster model development

The Russian transport system is in seriously need of renovation and improvement its competitiveness in the international logistics area. In this article it is proposed one of the potential variant of solving this challenging task-it is a creation of transport&logistics cluster. Transport&logistics cluster is a new organizational form, which purpose will be to increase not only the quality of transport services, but also the maximization of the effectiveness of the activities of all the participants in the association. © Published under licence by IOP Publishing Ltd

Fingerprints of Spin-Orbital Physics in Crystalline O2_2

The alkali hyperoxide KO$_2$ is a molecular analog of strongly-correlated systems, comprising of orbitally degenerate magnetic O$_2^-$ ions. Using first-principles electronic structure calculations, we set up an effective spin-orbital model for the low-energy \textit{molecular} orbitals and argue that many anomalous properties of KO$_2$ replicate the status of its orbital system in various temperature regimes.Comment: 4 pages, 2 figures, 1 tabl

Spin States of Cobalt Ions in the Bulk and on the Surface of LaCoO3 Probed by X-ray Absorption, Emission, and Photoelectron Spectra

We present X-ray photoelectron, Co L2,3 and O K X-ray absorption, as well as Co Kβ1,3 X-ray emission spectroscopy results of studies of the spin states of trivalent cobalt ions in single-crystal cobaltite LaCoO3. We show that at room temperature, in the bulk of a LaCoO3 single crystal, Co3+ ions are in the low-spin state, while high-spin Co2+, high-spin Co3+, low-spin Co3+ , and probably also intermediate-spin Co3+ ions are localated on the surface

The Hubble flow around the CenA / M83 galaxy complex

We present HST/ACS images and color-magnitude diagrams for 24 nearby galaxies in and near the constellation of Centaurus with radial velocities V_LG < 550 km/s. Distances are determined based on the luminosities of stars at the tip of the red giant branch that range from 3.0 Mpc to 6.5 Mpc. The galaxies are concentrated in two spatially separated groups around Cen A (NGC 5128) and M 83 (NGC 5236). The Cen A group itself has a mean distance of 3.76 +/-0.05 Mpc, a velocity dispersion of 136 km/s, a mean harmonic radius of 192 kpc, and an estimated orbital/virial mass of (6.4 - 8.1) x 10^12 M_sun. This elliptical dominated group is found to have a relatively high mass-to-light ratio: M/L_B = 125 M_sun/L_sun. For the M 83 group we derived a mean distance of 4.79 +/-0.10 Mpc, a velocity dispersion of 61 km/s, a mean harmonic radius of 89 kpc, and estimated orbital/virial mass of (0.8 - 0.9) x 10^12 M_sun. This spiral dominated group is found to have a relatively low M/L_B = 34 M_sun/L_sun. The radius of the zero-velocity surface around Cen A lies at R_0 = 1.40 +/-0.11 Mpc, implying a total mass within R_0 of M_T = (6.0 +/-1.4) x 10^12 M_sun. This value is in good agreement with the Cen A virial/orbital mass estimates and provides confirmation of the relatively high M/L_B of this elliptical-dominated group. The centroids of both the groups, as well as surrounding field galaxies, have very small peculiar velocities, < 25 km/s, with respect to the local Hubble flow with H_0 = 68 km/s/Mpc.Comment: 31 pages including 9 figures and 3 tables. Accepted for publication in Astronomical Journal, 133, N0. 2 (February), 200

The Evolutionary Status of Isolated Dwarf Irregular Galaxies II. Star Formation Histories and Gas Depletion

The results of UBV and H alpha imaging of a large sample of isolated dwarf irregular galaxies are interpreted in the context of composite stellar population models. The observed optical colors are best fit by composite stellar populations which have had approximately constant star formation rates for at least 10 Gyr. The galaxies span a range of central surface brightness, from 20.5 to 25.0 mag arcsec^{-2}; there is no correlation between surface brightness and star formation history. Although the current star formation rates are low, it is possible to reproduce the observed luminosities without a major starburst episode. The derived gas depletion timescales are long, typically ~20 Gyr. These results indicate that dwarf irregular galaxies will be able to continue with their slow, but constant, star formation activity for at least another Hubble time. The sample of isolated dIs is compared to a sample of star bursting dwarf galaxies taken from the literature. The star bursting dwarf galaxies have many similar properties; the main difference between these two types of gas-rich dwarf galaxies is that the current star formation is concentrated in the center of the star bursting systems while it is much more distributed in the quiescent dIs. This results in pronounced color gradients for the starbursting dwarf galaxies, while the majority of the quiescent dwarf irregular galaxies have minor or non-existent color gradients. Thus, the combination of low current star formation rates, blue colors, and the lack of significant color gradients indicates that star formation percolates slowly across the disk of normal dwarf galaxies in a quasi-continuous manner.Comment: 16 pages, uses emulateapj, to appear in The Astronomical Journal (April 2001

Kramers-Kronig constrained variational analysis of optical spectra

A universal method of extraction of the complex dielectric function $\epsilon(\omega)=\epsilon_{1}(\omega)+i\epsilon_{2}(\omega)$ from experimentally accessible optical quantities is developed. The central idea is that $\epsilon_{2}(\omega)$ is parameterized independently at each node of a properly chosen anchor frequency mesh, while $\epsilon_{1}(\omega)$ is dynamically coupled to $\epsilon_{2}(\omega)$ by the Kramers-Kronig (KK) transformation. This approach can be regarded as a limiting case of the multi-oscillator fitting of spectra, when the number of oscillators is of the order of the number of experimental points. In the case of the normal-incidence reflectivity from a semi-infinite isotropic sample the new method gives essentially the same result as the conventional KK transformation of reflectivity. In contrast to the conventional approaches, the proposed technique is applicable, without readaptation, to virtually all types of linear-response optical measurements, or arbitrary combinations of measurements, such as reflectivity, transmission, ellipsometry {\it etc.}, done on different types of samples, including thin films and anisotropic crystals.Comment: 10 pages, 7 figure