149 research outputs found
Surface Brightness Gradients Produced by the Ring Waves of Star Formation
We compute surface brightness profiles of galactic disks for outwardly
propagating waves of star formation with a view to investigate the stellar
populations in ring galaxies. We consider two mechanisms which can create
outwardly propagating star forming rings in a purely gaseous disk --- a
self-induced wave and a density wave. We show that the surface brightness
profiles produced by both scenarios of ring formation are similar and are
strongly sensitive to the velocity of the wave. The results of our computations
are compared with the observational quantities sensitive to the young and old
stellar populations in the ring galaxies A0035-335 (the Cartwheel galaxy) and
VIIZw466. The best fit to the observed radial H_alpha surface brightness
distribution in the Cartwheel galaxy is obtained for a wave velocity of about
90 km/s. The red continuum brightness of the ring can be fully explained by the
evolving stars present in the trailing part of the wave. However the red
continuum brightness in regions internal to the ring indicates that the wave of
star formation propagates in a pre-existing stellar disk in the Cartwheel. The
H_alpha and K-band surface brightness profiles in VIIZw466 match the values
expected from stellar populations produced by a wave of star formation
propagating in a purely gaseous disk very well. We conclude that VIIZw466 is
probably experiencing the first event of star formation in the disk.Comment: Uses aas2pp4.sty and epsfig.sty, 15 pages To appear in Astrophysical
Journal, March 10, 199
Chemical Abundance Gradients in the Star-Forming Ring Galaxies
Ring waves of star formation, propagating outwardly in the galactic disks,
leave chemical abundance gradients in their wakes. We show that the relative
[Fe/O] abundance gradients in ring galaxies can be used as a tool for
determining the role of the SNIa explosions in their chemical enrichment. We
consider two mechanisms which can create outwardly propagating star forming
rings in a purely gaseous disk -- a self-induced wave and a density wave, and
demonstrate that the radial distribution of the relative [Fe/O] abundance
gradients does not depend on the particular mechanism of the wave formation or
on the parameters of the star-forming process. We show that the [Fe/O] profile
is determined by the velocity of the wave, initial mass function, and the
initial chemical composition of the star-forming gas. If the role of SNIa
explosions is negligible in the chemical enrichment, the ratio [Fe/O] remains
constant throughout the galactic disk with a steep gradient at the wave front.
If SNIa stars are important in the production of cosmic iron, the [Fe/O] ratio
has gradient in the wake of the star-forming wave with the value depending on
the frequency of SNIa explosions.Comment: Uses aas2pp4.sty and epsfig.sty, 7 pages including one figure To
appear in Astrophysical Journa
Formation of Plumes in Head-on Collisions of Galaxies
Using N-body and SPH modeling we perform 3D numerical simulations of head-on
collisions between gas rich disk galaxies, including collisions between
counter-rotating disks and off-center collisions. Pure stellar intruders do not
produce gaseous plumes similar to those seen in the Cartwheel and VII Zw466
complexes of interacting galaxies; the presence of gas in an intruder galaxy
and radiative cooling are important for the formation of a gaseous plume
extending from the disk of a target galaxy. A noticeable plume structure can be
formed if the mass of an intruder is a few percent of the mass of the primary.
The halo of the intruder is stripped in the collision, and dispersed
particles form a broad stellar bridge connecting the two galaxies. The fraction
of the intruder's halo dispersed in the collision depends on the total mass of
the intruder, and low-mass intruders lose most of their mass.Comment: 15 pages, 14 figures in GIF. To appear ApJ. Vol. 505 #
Origin of TeV Galactic Cosmic Rays
We consider a possibility of identification of sources of cosmic rays (CR) of
the energy above 1 TeV via observation of degree-scale extended gamma-ray
emission which traces the locations of recent sources in the Galaxy. Such
emission in the energy band above 100 GeV is produced by CR nuclei and
electrons released by the sources and spreading into the interstellar medium.
We use the data from the Fermi gamma-ray telescope to locate the degree-scale
100 GeV gamma-ray sources. We find that the number of such sources and their
overall power match to those expected when CRs injection events happen every
~100 yr in portions of ~1e50 erg. We find that most of the sources are
associated to pulsars with spin down age less than ~30 kyr and hence to the
recent supernova explosions. This supports the hypothesis of supernova origin
of Galactic CRs. We notice that the degree-scale extended emission does not
surround shell-like supernova remnants without pulsars. Based on this
observation, we argue that the presence of the pulsar is essential for the CR
acceleration process. We expect that a significant fraction of the degree-scale
sources should be detectable as extended sources with km3-scale neutrino
detectors.Comment: 14 pages, 14 figures, accepted for publication in Phys.Rev.
The using of quality indicators of Scots pine’s seeds for bioindication of anthropogenic pollution
The quality of Scots pine’s seeds (Pinus sylvestris L.) was analyzed in conditions of industrial emissions magnesite productionПроанализировано качество семян сосны обыкновенной (Pinus sylvestris L.) в условиях промышленных выбросов магнезитового производств
Psychology features of older people in tourism
On the basis of the analysis of elderly people’s tourist activity the factors determining the organization of tourist activity have been revealed. The psychological features of elderly tourists, causing their consumer behavior, both in the process of purchasing tourist permits, and the General attitude of the consumer to tourism have been considered. It has been established that stereotypes, the environment of tourist products and the emotional sphere of the elderly tourist are the main factors, on the basis of which the decision on travel or refusal to travel is made. The model of interaction process of psychological features of elderly tourists with stages of tourist activity has been presented. The dependence between the primary experience of tourism and the subsequent recreational needs refl cts the importance of studying the psychology of elderly tourists to ensure the frequency of consumption of tourist products
Scots pine as a bioindicator of the aerotechnogenic pollution
The investigations of the conditions of the Scots pine stands in the conditions of the aerotechnogenic emissions of the magnesite industry were provided. It is shown that the weak level of pollution had an negative impact on both the vegetative and generative system of Scots pine. It is concluded that the pine species had high sensibility to the alkaline aeropollutantsПроведены исследования состояния культур сосны обыкновенной (Pinus sylvestris L.) в условиях аэротехногенных выбросов магнезитового производства. Показано, что даже слабый уровень загрязнения негативно влияет как на вегетативную, так и на генеративную системы сосны. Сделан вывод о высокой чувствительности данного вида хвойных к щелочным аэрополлютанта
Molecular genetic characteristics of Darevskia portschinskii lizard populations based on microsatellite markers analysis
The Caucasian rock lizard species Darevskia portschinskii is one of the bisexual species participating in interspecific hybridisation as the paternal ancestor with the maternal ancestors D. mixta and D. raddei resulting in the successful formation of the parthenogenetic D. dahli and D. rostombekowi, respectively. Populations of D. portschinskii have been previously divided into two subspecies, D. p. portschinskii and D. p. nigrita according to their geographical distribution and the morphological data, but they have not been characterised genetically. Here, we used ten microsatellite markers to determine the genetic structure of the D. portschinskii populations. The utility of the developed microsatellite markers for investigating the genetic variability within and among populations with a heterogeneous spatial distribution was demonstrated. Our results showed that the intra- and interspecific differentiation of the studied populations were consistent with the morphological data on the subspecies status of the D. p. portschinskii and D. p. nigrita populations. A potential applicability of the developed microsatellite markers to study genetic diversity of Darevskia species and subspecies complexes is suggested
Gravitational stability and dynamical overheating of stellar disks of galaxies
We use the marginal stability condition for galactic disks and the stellar
velocity dispersion data published by different authors to place upper limits
on the disk local surface density at two radial scalelengths .
Extrapolating these estimates, we constrain the total mass of the disks and
compare these estimates to those based on the photometry and color of stellar
populations. The comparison reveals that the stellar disks of most of spiral
galaxies in our sample cannot be substantially overheated and are therefore
unlikely to have experienced a significant merging event in their history. The
same conclusion applies to some, but not all of the S0 galaxies we consider.
However, a substantial part of the early type galaxies do show the stellar
velocity dispersion well in excess of the gravitational stability threshold
suggesting a major merger event in the past. We find dynamically overheated
disks among both seemingly isolated galaxies and those forming pairs. The ratio
of the marginal stability disk mass estimate to the total galaxy mass within
four radial scalelengths remains within a range of 0.4---0.8. We see no
evidence for a noticeable running of this ratio with either the morphological
type or color index.Comment: 25 pages, 5 figures, accepted to Astronomy Letter
Dynamics of Gaseous Disks in a Non-axisymmetric Dark Halo
The dynamics of a galactic disk in a non-axisymmetric (triaxial) dark halo is
studied in detail using high-resolution, numerical, hydrodynamical models. A
long-lived, two-armed spiral pattern is generated for a wide range of
parameters. The spiral structure is global, and the number of turns can be two
or three, depending on the model parameters. The morphology and kinematics of
the spiral pattern are studied as functions of the halo and disk parameters.
The spiral structure rotates slowly, and its angular velocity varies
quasi-periodically. Models with differing relative halo masses, halo semi-axis
ratios, distributions of matter in the disk, Mach numbers in the gaseous
component, and angular rotational velocities of their halos are considered.Comment: 22 pages, 11 figure
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