246 research outputs found
Optical Color Gradients in Star-Forming Ring Galaxies
We compute radial color gradients produced by an outwardly propagating
circular wave of star formation and compare our results with color gradients
observed in the classical ring galaxy, the ``Cartwheel''. We invoke two
independent models of star formation in the ring galaxies. The first one is the
conventional density wave scenario, in which an intruder galaxy creates a
radially propagating density wave accompanied by an enhanced star formation
following the Schmidt law. The second scenario is a pure self-propagating star
formation model, in which the intruder only sets off the first burst of stars
at the point of impact. Both models give essentially the same results.
Systematic reddening of B-V, V-K colors towards the center, such as that
observed in the Cartwheel, can be obtained only if the abundance of heavy
elements in the star-forming gas is a few times below solar. The B-V and V-K
color gradients observed in the Cartwheel can be explained as a result of
mixing of stellar populations born in a star-forming wave propagating through a
low-metallicity gaseous disk, and a pre-existing stellar disk of the size of
the gaseous disk with color properties typical to those observed in nearby disk
galaxies.Comment: 16 pages, 12 figures; accepted for publication in the Astrophysical
Journa
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
Secrecy of communications in data transmission by impulses with unknown moments of appearance and disappearance
We carried out a comparative analysis of the algorithms for detecting a rectangular impulse against Gaussian white noise under either authorized or unauthorized access to the tr ansmitted data. We presupposed that for data transmission the binary communication system is used and that the useful information in the data is whether the signal is present or absent. The case is that unauthorized access by the outsider takes place in the situation when the signal parameters are completely or partially unknown. We then define the degree of the transmitted data secrecy by the secrecy ratio determining how highly the threshold signal-to-noise ratio increases when there is the unauthorized access instead of the authorized one
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
Water Resources Management In Support Of Raw Region Based On Decoupling Effect
It determines the presence of the decoupling effect in the Russians raw regions materials by using water. Developed models that explain the relationship between the gross regional product and water intake. It proved no effect on the growth of water consumption in most regions of the reference commodity. Recommendations for the decoupling effect development in support of Russians raw regions
The Multiband Photometry of GRB Host Galaxies: Comparison with the Spectral Energy Distributions of Nearby and Theoretical Modeling Galaxies
We present one of the results of photometry of the hosts of GRB for
the host galaxy of GRB 970508 and the theoretical modeling of its continuum
spectral energy distribution (SED) to show that it is important to take into
account internal extinction in the host galaxies. We compared the BVRI
broad-band flux spectrum of the host to template SEDs of local starburst
galaxies and found that there is a significant internal extintion in this host.
Moreover, this comparison allows us to derive the absolute magnitude
(M_{B_{rest}}) and rouhgly estimate reddening (A_V). Population synthesis
modeling of the continuum SED for different reddening laws demostrates that the
observational data of the host galaxy of GRB 970508 are best fitted by the
spectral properties of a model SED with extinction of A_V\approx 2.Comment: 3 pages, 2 figures, poster presentation on 2nd Rome Workshop on
Gamma-Ray Bursts in the Afterglow Er
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