2,166 research outputs found
Wide-field multi-color photometry of the Galactic globular cluster NGC 1261
(Abriged)This work studies in more detail the stellar population, including
its photometric properties and characteristics, in the rarely studied southern
Galactic globular cluster NGC 1261. We focus on the brighter sequences of the
cluster's color-magnitude diagram (CMD). Like in our previous works, we rely
upon photometry in several passbands to achieve more reliable results and
conclusions. We carried out and analyzed new multi-color photometry of NGC 1261
in UBVI reaching below the turnoff point in all passbands in a fairly extended
cluster field, about 14'x14'. We found several signs of the inhomogeneity
("multiplicity") in the stellar population. The most prominent of them are: (1)
the dependence of the radial distribution of sub-giant branch (SGB) stars in
the cluster on their U magnitude, with brighter stars less centrally
concentrated at the 99.9 \% level than their fainter counterparts; (2) the
dependence of the location of red giant branch (RGB) stars in the U-(U-B) CMD
on their radial distance from the cluster center, with the portion of stars
bluer in the (U-B) color increasing towards the cluster outskirts.
Additionally, the radial variation of the RGB luminosity function in the bump
region is suspected. We assume that both the SGB stars brighter in the U and
the RGB stars bluer in the (U-B) color are probably associated with blue
horizontal branch stars, because of a similarity in their radial distribution
in the cluster. We estimated the metalicity of NGC 1261 from the slope of the
RGB in U-based CMDs and the location of the RGB bump on the branch. These
metallicity indicators give [Fe/H]zw = -1.34 +/- 0.16 dex and [Fe/H]zw = -1.41
+/- 0.10 dex, respectively. We isolated 18 probable blue straggler candidates.
They are more centrally concentrated than the lower red giants of comparable
brightness at the 97.9 \% level.Comment: 8 pages, 9 figures, accepted for publication in A&
Evidence of the inhomogeneity of the stellar population in the differentially reddened globular cluster NGC 3201
We report on evidence of the inhomogeneity (multiplicity) of the stellar
population in the Galactic globular cluster (GC) NGC 3201, which is irregularly
reddened across its face. We carried out a more detailed and careful analysis
of our recently published new multi-color photometry in a wide field of the
cluster with particular emphasis on the U band. Using the photometric data
corrected for differential reddening, we found for the first time two key signs
of the inhomogeneity in the cluster's stellar population and of its radial
variation in the GC. These are (1) an obvious trend in the color-position
diagram, based on the (U-B) color-index, of red giant branch (RGB) stars, which
shows that the farther from the cluster's center, the bluer on average the
(U-B) color of the stars is; and (2) the dependence of the radial distribution
of sub-giant branch (SGB) stars in the cluster on their U magnitude, where
brighter stars are less centrally concentrated than their fainter counterparts
at a confidence level varying between 99.2% and 99.9% depending on the
color-index used to select the stars. The same effects were recently found by
us in the GC NGC 1261. However, contrary to NGC 1261, we are not able to
unambiguously suggest which of the sub-populations of SGB/RGB stars can be the
progenitor of blue and red horizontal branch stars of the cluster. Apart from
M4, NGC 3201 is another GC very probably with an inhomogeneous stellar
population, which has essentially lower mass than the most massive Galactic GCs
where multiple stellar populations were unambiguously detected for the first
timeComment: 5 pages, 4 figure
Strong radial segregation between sub-populations of evolutionary homogeneous stars in the Galactic globular cluster NGC 6752
We investigate the new and still poorly studied matter of so-called multiple
stellar populations (MSPs) in Galactic globular clusters (GGCs). Studying MSPs
and their accumulated data can shed more light on the formation and evolution
of GGCs and other closely related fundamental problems. We focus on the strong
relation between the radial distribution of evolutionary homogeneous stars and
their U-based photometric characteristics in the nearby GGC NGC 6752 and
compare this with a similar relation we found in NGC 3201 and NGC 1261. We use
our new multi-color photometry in a fairly wide field of NGC 6752, with
particular emphasis on the U band and our recent and already published
photometry made in NGC 3201 and NGC 1261. We found and report here for the
first time a strong difference in the radial distribution between the
sub-populations of red giant branch (RGB) stars that are bluer and redder in
color U-B, as well as between sub-giant branch (SGB) stars brighter and fainter
in the U-magnitude in NGC 6752. Moreover, the fainter SGB and redder RGB stars
are similarly much more centrally concentrated than their respective brighter
and bluer counterparts. Virtually the same applies to NGC 3201. We find
evidence in NGC 6752 as in NGC 3201 that a dramatic change in the proportion of
the two sub-populations of SGB and RGB stars occurs at a radial distance close
to the half-mass radius, R_h, of the cluster. These results are the first
detections of the radial trend of the particular photometric properties of
stellar populations in GGCs. They imply a radial dependence of the main
characteristics of the stellar populations in these GGCs, primarily of the
abundance, and (indirectly) presumably of the kinematics.Comment: 5 pages, 5 figures, accepted for publication in Astronomy and
Astrophysics (Letters
SPECTRAL CORRELATIONS IN DISORDERED ELECTRONIC SYSTEMS: CROSSOVER FROM METAL TO INSULATOR REGIME
We use the semiclassical approach combined with the scaling results for the
diffusion coefficient to consider the two-level correlation function
for a disordered electron system in the crossover region,
characterized by the appearance of a macroscopic correlation or localization
length, , that diverges at the metal-insulator transition. We show new
critical statistics, characterized by a nontrivial asymptotic behavior of
, to emerge on both sides of the transition at higher energies,
and to expand to all energies larger than mean level spacing when exceeds
the system size.Comment: 4 pages,1 figure, in self-ectracting uuencoded gz-compressed file to
be published in Phys. Rev. Letters; REVTeX source file is available upon
reques
The Level Spacing Distribution Near the Anderson Transition
For a disordered system near the Anderson transition we show that the
nearest-level-spacing distribution has the asymptotics for s\gg \av{s}\equiv 1 which is universal and intermediate
between the Gaussian asymptotics in a metal and the Poisson in an insulator.
(Here the critical exponent and the numerical coefficient
depend only on the dimensionality ). It is obtained by mapping the energy
level distribution to the Gibbs distribution for a classical one-dimensional
gas with a pairwise interaction. The interaction, consistent with the universal
asymptotics of the two-level correlation function found previously, is proved
to be the power-law repulsion with the exponent .Comment: REVTeX, 8 pages, no figure
Multi-Color Photometry of the Galactic Globular Cluster M75 = NGC 6864. A New Sensitive Metallicity Indicator and the Position of the Horizontal Branch in UV
We carry out and analyze new multi-color photometry of the Galactic globular
cluster (GC) M75 in UBVI and focus on the brighter sequences of the color-
magnitude diagram (CMD), with particular emphasis on their location in U-based
CMD. Specifically, we study the level both of the horizontal (HB) and red giant
branches (RGB) relative to the main-sequence turnoff (TO) in the U magnitude.
Along with the presented photometry of M75, we use our collection of
photometric data on GCs belonging to the metal-poor range, [Fe/H]zw<-1.1 dex,
obtained from observations with different equipment, but calibrated by standard
stars situated in the observed cluster fields. We confirm our earlier finding,
and extend it to a larger magnitude range.We demonstrate that DeltaU_{TO}^{BHB}
expressing the difference in U magnitude between the TO point and the level of
the blue HB, near its red boundary, of the metal-poor GCs observed with the
EMMI camera of the NTT/ESO telescope is about 0.4-0.5 mag smaller as compared
to GCs observed with the 100" telescope and 1.3 m Warsaw telescope of the Las
Campanas Observatory. At the same time, Delta U_{TO}^{RGB}, the difference in U
magnitude between the TO and RGB inflection (brightest) points, does not show
such an apparent dependence on the characteristics of U filters used, but it
depends on cluster metallicity. We have shown, for the first time, the
dependence of the parameter DeltaU_{TO}^{RGB} on [Fe/H] and have estimated its
analytical expression, by assuming a linear relation between the parameter and
metallicity. Its slope, Delta U_{TO}^{RGB}/Delta [Fe/H]~1.2 mag/dex, is approx.
a factor of two steeper than that of the dependence of the RGB bump position in
the V magnitude on metallicity. The asymptotic giant branch (AGB) clump and
features of the RGB luminosity function (LF) of M75 are also discussed.Comment: 9 pages, 7 figures, accepted for publication in A&
Escape of Ionizing Radiation from High Redshift Galaxies
We model the escape of ionizing radiation from high-redshift galaxies using
high-resolution Adaptive Mesh Refinement N-body + hydrodynamics simulations.
Our simulations include time-dependent and spatially-resolved transfer of
ionizing radiation in three dimensions, including effects of dust absorption.
For galaxies of total mass M > 10^11 Msun and star formation rates SFR ~ 1-5
Msun/yr, we find angular averaged escape fractions of 0.01-0.03 over the entire
redshift interval studied (3<z<9). In addition, we find that the escape
fraction varies by more than an order of magnitude along different
lines-of-sight within individual galaxies, from the largest values near
galactic poles to the smallest along the galactic disk. The escape fraction
declines steeply at lower masses and SFR. We show that the low values of escape
fractions are due to a small fraction of young stars located just outside the
edge of HI disk. We compare our predicted escape fraction of ionizing photons
with previous results, and find a general agreement with both other simulation
results and available direct detection measurements at z ~ 3. We also compare
our simulations with a novel method to estimate the escape fraction in galaxies
from the observed distribution of neutral hydrogen column densities along the
lines of sights to long duration gamma-ray bursts. Using this method we find
escape fractions of the GRB host galaxies of 2-3%, consistent with our
theoretical predictions. [abridged]Comment: submitted to Ap
Spin and orbital Hall effects for diffracting optical beams in gradient-index media
We examine the evolution of paraxial beams carrying intrinsic spin and
orbital angular momenta (AM) in gradient-index media. A parabolic-type equation
is derived which describes the beam diffraction in curvilinear coordinates
accompanying the central ray. The center of gravity of the beam experiences
transverse AM-dependent deflections -- the spin and orbital Hall effects. The
spin Hall effect generates a transverse translation of the beam as a whole, in
precise agreement with recent geometrical optics predictions. At the same time,
the orbital Hall effect is significantly affected by the diffraction in the
inhomogeneous medium and is accompanied by changes in the intrinsic orbital AM
and deformations of the beam.Comment: 4 pages, 2 figures, to appear in Phys. Rev.
Change of cosmic ray anisotropy with solar activity
Muon telescope data at various depths underground in Yakutsk within energy range 10 to 300 GeV for 1957 to 1984 are analyzed. The 22-year variation of the interplanetary magnetic field aligned component is found. The variation is caused by interaction of heliomagnetosphere with the local galactic field and interstellar wind
On problem of polarization tomography, I
The polarization tomography problem consists of recovering a matrix function
f from the fundamental matrix of the equation
known for every geodesic of a given Riemannian metric. Here
is the orthogonal projection onto the hyperplan
. The problem arises in optical tomography of slightly
anisotropic media. The local uniqueness theorem is proved: a - small
function f can be recovered from the data uniquely up to a natural obstruction.
A partial global result is obtained in the case of the Euclidean metric on
- …