512 research outputs found
On ionisation effects and abundance ratios in damped Lyman-alpha systems
The similarity between observed velocity structures of Al III and singly
ionised species in damped Lyman-alpha systems (DLAs) suggests the presence of
ionised gas in the regions where most metal absorption lines are formed.
To explore the possible implications of ionisation effects we construct a
simplified two-region model for DLAs consisting of an ionisation bounded region
with an internal radiation field and a neutral region with a lower metal
content. Within this framework we find that ionisation effects are important.
If taken into account, the element abundance ratios in DLAs are quite
consistent with those observed in Milky Way stars and in metal-poor H II
regions in blue compact dwarf galaxies. In particular we cannot exclude the
same primary N origin in both DLAs and metal-poor galaxies. From our models no
dust depletion of heavy elements needs to be invoked; little depletion is
however not excluded.Comment: to appear in "Evolution of Galaxies. I. Observational clues", Eds.
J.M. Vilchez, G. Stasinska, Astrophysics and Space Science, in press. 5
pages, including 3 figure
A New Approach to Systematic Uncertainties and Self-Consistency in Helium Abundance Determinations
Tests of big bang nucleosynthesis and early universe cosmology require
precision measurements for helium abundance determinations. However, efforts to
determine the primordial helium abundance via observations of metal poor H II
regions have been limited by significant uncertainties. This work builds upon
previous work by providing an updated and extended program in evaluating these
uncertainties. Procedural consistency is achieved by integrating the hydrogen
based reddening correction with the helium based abundance calculation, i.e.,
all physical parameters are solved for simultaneously. We include new atomic
data for helium recombination and collisional emission based upon recent work
by Porter et al. and wavelength dependent corrections to underlying absorption
are investigated. The set of physical parameters has been expanded here to
include the effects of neutral hydrogen collisional emission. Because of a
degeneracy between the solutions for density and temperature, the precision of
the helium abundance determinations is limited. Also, at lower temperatures (T
\lesssim 13,000 K) the neutral hydrogen fraction is poorly constrained
resulting in a larger uncertainty in the helium abundances. Thus the derived
errors on the helium abundances for individual objects are larger than those
typical of previous studies. The updated emissivities and neutral hydrogen
correction generally raise the abundance. From a regression to zero
metallicity, we find Y_p as 0.2561 \pm 0.0108, in broad agreement with the WMAP
result. Tests with synthetic data show a potential for distinct improvement,
via removal of underlying absorption, using higher resolution spectra. A small
bias in the abundance determination can be reduced significantly and the
calculated helium abundance error can be reduced by \sim 25%.Comment: 51 pages, 13 figure
The metallicities of UM151, UM408 and A1228+12 revisited
We present the results of new spectrophotometry and heavy element abundance
determinations for 3 dwarf galaxies UM151, UM408 and A1228+12 (RMB132). These
galaxies have been claimed in the literature to have very low metallicities,
corresponding to log(O/H)+12 < 7.65, that are in the metallicity range of some
candidate local young galaxies. We present higher S/N data for these three
galaxies. UM151 and UM408 have significantly larger metallicities: log(O/H)+12
= 8.5 and 7.93, respectively. For A1228+12 our new log(O/H)+12 = 7.73 is close
to that recalculated from earlier data (7.68). Thus, the rederived
metallicities allow us to remove these objects from the list of galaxies with Z
< 1/20 Z_Sun.Comment: LaTeX, 8 pages with 3 Postscript figures, A&A in pres
Formation of the system of management of supporting university on the basis of strengthening of communication component
The article deals with changes in the system of management of educational establishments of higher education caused by creation of supporting universities. The program of creation of such universities supposes formation of universities-leaders in regions, which can consolidate educational and scientific basis for training of personnel in Russian subjects. During creation of supporting regional universities, the emphasis is made on the fact that they are to become the centers of innovational development, being a part of economy and region’s infrastructure at the same time. At that, creation of new engineering and implemental centers and R&D laboratories requires complex realization of projects for creation of high-tech production and necessary conditions for development of interface of regional supporting universities and enterprises. The article views functions and organizational structure of management of technical university; establishes dependence of intensity of organizational transformations on various factors. The authors show a process of formation of matrix organizational structure of technical supporting university with the use of mobile informational and communicational structures, which is formed by placement of horizontal connections on existing linear and functional structure.peer-reviewe
Model of creation and management of the process of technological projects development
The purpose of the article is to determine and describe main principles and model of development of regional business accelerator on the basis of technical university for development of innovational startups. The research included the work on identification of the problems of the process of commercialization of technological developments, which business accelerator should solve. One of the basic purposes of creation of business accelerator is increase of the flow of prepared projects for consideration by investment committees of funds of early stages. Accelerator can be a full-scale unified mechanism of formation of deals flow from diversified mass of completed R&D. As a result of the research, the authors come to a conclusion that the process of creation of value and movement from prototype to entering a market supposes long chain with formation of various risks at each stage – scientific, financial, administrative, etc. Minimization of such risks requires from partners, involved with the work of business accelerator, solving emerging problems together. Such motivation could be formed by development of business accelerator by the principles of partnership and creation of equal access and rights for basic members.peer-reviewe
HS 2134+0400 - new very metal-poor galaxy, a representative of void population?
We present the SAO 6m telescope spectroscopy of a blue compact galaxy (BCG)
HS 2134+0400 discovered in frame of the dedicated Hamburg/SAO survey for Low
Metallicity BCGs (HSS-LM). Its very low abundance of oxygen (12+log(O/H) =
7.44), as well as other heavy elements (S, N, Ne, Ar), assigns this dwarf
galaxy to the group of BCGs with the lowest metal content. There are only eight
that low metallicity among several thousand known BCGs in the nearby Universe.
The abundance ratios for the heavy elements (S/O, Ne/O, N/O, and Ar/O) are well
consistent with the typical values of other very metal-poor BCGs. The global
environment of HS 2134+0400 is atypical of the majority of BCGs. The object
falls within the Pegasus void, the large volume with the very low density of
galaxies with the normal (M_B* = -19.6) or high luminosity. Since we found in
voids a dozen more the very metal-poor galaxies, we discuss the hypothesis that
such objects can be representative of a substantial fraction of the void dwarf
galaxy population.Comment: 6 pages, including 2 tables and 2 postscript figures. Submitted to
Astronomy Letter
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