4,239 research outputs found
Freeze-Out Time in Ultrarelativistic Heavy Ion Collisions from Coulomb Effects in Transverse Pion Spectra
The influence of the nuclear Coulomb field on transverse spectra of
and measured in reactions at 158 A GeV has been investigated.
Pion trajectories are calculated in the field of an expanding fireball. The
observed enhancement of the ratio at small momenta depends on the
temperature and transverse expansion velocity of the source, the rapidity
distribution of the net positive charge, and mainly the time of the freeze-out.Comment: 11 pages including 2 figure
Observations of Lick Standard Stars Using the SCORPIO Multi-Slit Unit at the SAO 6-m Telescope
We present Lick line-index measurements of standard stars from the list of
Worthey. The spectra were taken with the multi-slit unit of the SCORPIO
spectrograph at the 6-m Special Astrophysical observatory telescope. We
describe in detail our method of analysis and explain the importance of using
the Lick index system for studying extragalactic globular clusters. Our results
show that the calibration of our instrumental system to the standard Lick
system can be performed with high confidence.Comment: 12 pages, 3 figure
Synchronous Evolution of Galaxies in Groups: NGC 524 Group
By means of panoramic spectroscopy at the SAO RAS BTA telescope, we
investigated the properties of stellar populations in the central regions of
five early-type galaxies -- the NGC 524 group members. The evolution of the
central regions of galaxies looks synchronized: the average age of stars in the
bulges of all the five galaxies lies in the range of 3--6 Gyr. Four of the five
galaxies revealed synchronized bursts of star formation in the nuclei 1--2 Gyr
ago. The only galaxy, in which the ages of stellar population in the nucleus
and in the bulge coincide (i.e. the nuclear burst of star formation did not
take place) is NGC 502, the farthest from the center of the group of all the
galaxies studied.Comment: Slightly edited version of the paper to appear in the Astrophysical
Bulletin, 67(3); 24 pages including 8 figure
Predictions for the Cosmogenic Neutrino Flux in Light of New Data from the Pierre Auger Observatory
The Pierre Auger Observatory (PAO) has measured the spectrum and composition
of the ultrahigh energy cosmic rays with unprecedented precision. We use these
measurements to constrain their spectrum and composition as injected from their
sources and, in turn, use these results to estimate the spectrum of cosmogenic
neutrinos generated in their propagation through intergalactic space. We find
that the PAO measurements can be well fit if the injected cosmic rays consist
entirely of nuclei with masses in the intermediate (C, N, O) to heavy (Fe, Si)
range. A mixture of protons and heavier species is also acceptable but (on the
basis of existing hadronic interaction models) injection of pure light nuclei
(p, He) results in unacceptable fits to the new elongation rate data. The
expected spectrum of cosmogenic neutrinos can vary considerably, depending on
the precise spectrum and chemical composition injected from the cosmic ray
sources. In the models where heavy nuclei dominate the cosmic ray spectrum and
few dissociated protons exceed GZK energies, the cosmogenic neutrino flux can
be suppressed by up to two orders of magnitude relative to the all-proton
prediction, making its detection beyond the reach of current and planned
neutrino telescopes. Other models consistent with the data, however, are
proton-dominated with only a small (1-10%) admixture of heavy nuclei and
predict an associated cosmogenic flux within the reach of upcoming experiments.
Thus a detection or non-detection of cosmogenic neutrinos can assist in
discriminating between these possibilities.Comment: 10 pages, 7 figure
NGC 7331: the Galaxy with the Multicomponent Central Region
We present the results of the spectral investigation of the regular Sb galaxy
NGC 7331 with the Multi-Pupil Field Spectrograph of the 6m telescope. The
absorption-line indices H-beta, Mgb, and are mapped to analyse the
properties of the stellar populations in the circumnuclear region of the
galaxy. The central part of the disk inside ~3" (200 pc) -- or a separate
circumnuclear stellar-gaseous disk as it is distinguished by decoupled fast
rotation of the ionized gas -- is very metal-rich, rather young, ~ 2 billion
years old, and its solar magnesium-to-iron ratio evidences for a very long
duration of the last episode of star formation there. However the gas
excitation mechanism now in this disk is shock-like. The star-like nucleus had
probably experienced a secondary star formation burst too: its age is 5 billion
years, much younger than the age of the circumnuclear bulge. But [Mg/Fe]=+0.3
and only solar global metallicity imply that the nuclear star formation burst
has been much shorter than that in the circumnuclear disk. The surrounding
bulge is rather old, 9--14 billion years old, and moderately metal-poor. The
rotation of the stars and gas within the circumnuclear disk is axisymmetric
though its rotation plane may be slightly inclined to the global plane of the
galaxy. Outside the circumnuclear disk the gas may experience non-circular
motions, and we argue that the low-contrast extended bulge of NGC 7331 is
triaxial.Comment: LATEX, 27 pages, + 15 Postscript figures. Accepted to Astronomical
Journal, July issu
A relativistic action-at-a-distance description of gravitational interactions?
It is shown that certain aspects of gravitation may be described using a
relativistic action-at-a-distance formulation. The equations of motion of the
model presented are invariant under Lorentz transformations and agree with the
equations of Einstein's theory of General Relativity, at the first
Post-Newtonian approximation, for any number of interacting point masses
Study of the structure and kinematics of the NGC 7465/64/63 triplet galaxies
This paper is devoted to the analysis of new observational data for the group
of galaxies NGC 7465/64/63, which were obtained at the 6-m telescope of the
Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS)
with the multimode instrument SCORPIO and the Multi Pupil Fiber Spectrograph.
For one of group members (NGC 7465) the presence of a polar ring was suspected.
Large-scale brightness distributions, velocity and velocity dispersion fields
of the ionized gas for all three galaxies as well as line-of-sight velocity
curves on the basis of emission and absorption lines and a stellar velocity
field in the central region for NGC 7465 were constructed. As a result of the
analysis of the obtained information, we revealed an inner stellar disk (r ~
0.5 kpc) and a warped gaseous disk in addition to the main stellar disk, in NGC
7465. On the basis of the joint study of photometric and spectral data it was
ascertained that NGC 7464 is the irregular galaxy of the IrrI type, whose
structural and kinematic peculiarities resulted most likely from the
gravitational interaction with NGC 7465. The velocity field of the ionized gas
of NGC 7463 turned out typical for spiral galaxies with a bar, and the bending
of outer parts of its disk could arise owing to the close encounter with one of
galaxies of the environment.Comment: 20 pages, 6 figure
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