216 research outputs found
Multi-frequency Studies of Massive Cores with Complex Spatial and Kinematic Structures
Five regions of massive star formation have been observed in various
molecular lines in the frequency range GHz. The studied regions
possess dense cores, which host young stellar objects. The physical parameters
of the cores are estimated, including kinetic temperatures ( K),
sizes of the emitting regions ( pc), and virial masses (). Column densities and abundances of various molecules are
calculated in the local thermodynamical equilibrium approximation. The core in
99.982+4.17, associated with the weakest IRAS source, is characterized by
reduced molecular abundances. Molecular line widths decrease with increasing
distance from the core centers (). For b\ga 0.1~pc, the dependences
are close to power laws (), where varies from
to , depending on the object. In four cores, the
asymmetries of the optically thick HCN(1--0) and HCO(1--0) lines indicate
systematic motions along the line of sight: collapse in two cores and expansion
in two others. Approximate estimates of the accretion rates in the collapsing
cores indicate that the forming stars have masses exceeding the solar mass.Comment: 18 pages, 7 figures, 6 table
Molecular line and continuum study of the W40 cloud
The dense cloud associated with W40, one of the nearby H II regions, has been
studied in millimeter-wave molecular lines and in 1.2 mm continuum. Besides,
1280 MHz and 610 MHz interferometric observations have been done. The cloud has
complex morphological and kinematical structure, including a clumpy dust ring
and an extended dense core. The ring is probably formed by the "collect and
collapse" process due to the expansion of neighboring H II region. Nine dust
clumps in the ring have been deconvolved. Their sizes, masses and peak hydrogen
column densities are: pc, and cm, respectively. Molecular lines are observed
at two different velocities and have different spatial distributions implying
strong chemical differentiation over the region. The CS abundance is enhanced
towards the eastern dust clump 2, while the NH, NH, and
HCO abundances are enhanced towards the western clumps. HCN and
HCO do not correlate with the dust probably tracing the surrounding gas.
Number densities derived towards selected positions are: cm. Two western clumps have kinetic temperatures 21 K and 16 K and
are close to virial equilibrium. The eastern clumps 2 and 3 are more massive,
have higher extent of turbulence and are probably more evolved than the western
ones. They show asymmetric CS(2--1) line profiles due to infalling motions
which is confirmed by model calculations. An interaction between ionized and
neutral material is taking place in the vicinity of the eastern branch of the
ring and probably trigger star formation.Comment: 16 pages, 6 figure
A Search for Small-Scale Clumpiness in Dense Cores of Molecular Clouds
We have analyzed HCN(1-0) and CS(2-1) line profiles obtained with high
signal-to-noise ratios toward distinct positions in three selected objects in
order to search for small-scale structure in molecular cloud cores associated
with regions of high-mass star formation. In some cases, ripples were detected
in the line profiles, which could be due to the presence of a large number of
unresolved small clumps in the telescope beam. The number of clumps for regions
with linear scales of ~0.2-0.5 pc is determined using an analytical model and
detailed calculations for a clumpy cloud model; this number varies in the
range: ~2 10^4-3 10^5, depending on the source. The clump densities range from
~3 10^5-10^6 cm^{-3}, and the sizes and volume filling factors of the clumps
are ~(1-3) 10^{-3} pc and ~0.03-0.12. The clumps are surrounded by inter-clump
gas with densities not lower than ~(2-7) 10^4 cm^{-3}. The internal thermal
energy of the gas in the model clumps is much higher than their gravitational
energy. Their mean lifetimes can depend on the inter-clump collisional rates,
and vary in the range ~10^4-10^5 yr. These structures are probably connected
with density fluctuations due to turbulence in high-mass star-forming regions.Comment: 23 pages including 4 figures and 4 table
On products of skew rotations
Let , be two time-independent Hamiltonians with one
degree of freedom and , be the one-parametric groups of
shifts along the orbits of Hamiltonian systems generated by , . In
some problems of population genetics there appear the transformations of the
plane having the form under some
conditions on , . We study in this paper asymptotical properties of
trajectories of .Comment: 13 pages, 10 figure
NGC 7538 : Multiwavelength Study of Stellar Cluster Regions associated with IRS 1-3 and IRS 9 sources
We present deep and high-resolution (FWHM ~ 0.4 arcsec) near-infrared (NIR)
imaging observations of the NGC 7538 IRS 1-3 region (in JHK bands), and IRS 9
region (in HK bands) using the 8.2m Subaru telescope. The NIR analysis is
complemented with GMRT low-frequency observations at 325, 610, and 1280 MHz,
molecular line observations of H13CO+ (J=1-0), and archival Chandra X-ray
observations. Using the 'J-H/H-K' diagram, 144 Class II and 24 Class I young
stellar object (YSO) candidates are identified in the IRS 1-3 region. Further
analysis using 'K/H-K' diagram yields 145 and 96 red sources in the IRS 1-3 and
IRS 9 regions, respectively. A total of 27 sources are found to have X-ray
counterparts. The YSO mass function (MF), constructed using a theoretical
mass-luminosity relation, shows peaks at substellar (~0.08-0.18 Msolar) and
intermediate (~1-1.78 Msolar) mass ranges for the IRS 1-3 region. The MF can be
fitted by a power law in the low mass regime with a slope of Gamma ~ 0.54-0.75,
which is much shallower than the Salpeter value of 1.35. An upper limit of 10.2
is obtained for the star to brown dwarf ratio in the IRS 1-3 region. GMRT maps
show a compact HII region associated with the IRS 1-3 sources, whose spectral
index of 0.87+-0.11 suggests optical thickness. This compact region is resolved
into three separate peaks in higher resolution 1280 MHz map, and the 'East'
sub-peak coincides with the IRS 2 source. H13CO+ (J=1-0) emission reveals peaks
in both IRS 1-3 and IRS 9 regions, none of which are coincident with visible
nebular emission, suggesting the presence of dense cloud nearby. The virial
masses are approximately of the order of 1000 Msolar and 500 Msolar for the
clumps in IRS 1-3 and IRS 9 regions, respectively.Comment: 27 pages, 18 figures, 5 tables. Accepted for publication in MNRA
Lorentz gauge theory as a model of emergent gravity
We consider a class of Lorentz gauge gravity theories within Riemann-Cartan
geometry which admits a topological phase in the gravitational sector. The
dynamic content of such theories is determined only by the contortion part of
the Lorentz gauge connection. We demonstrate that there is a unique Lagrangian
that admits propagating spin one mode in correspondence with gauge theories of
other fundamental interactions. Remarkably, despite the R^2 type of the
Lagrangian and non-compact structure of the Lorentz gauge group, the model
possesses rather a positive-definite Hamiltonian. This has been proved in the
lowest order of perturbation theory. This implies further consistent
quantization and leads to renormalizable quantum theory. It is assumed that the
proposed model describes possible mechanism of emergent Einstein gravity at
very early stages of the Universe due to quantum dynamics of contortion.Comment: 11 pages, final version, minor correction
First-Order Phase Transition in Potts Models with finite-range interactions
We consider the -state Potts model on , , ,
with Kac ferromagnetic interactions and scaling parameter \ga. We prove the
existence of a first order phase transition for large but finite potential
ranges. More precisely we prove that for \ga small enough there is a value of
the temperature at which coexist Gibbs states. The proof is obtained by a
perturbation around mean-field using Pirogov-Sinai theory. The result is valid
in particular for , Q=3, in contrast with the case of nearest-neighbor
interactions for which available results indicate a second order phase
transition. Putting both results together provides an example of a system which
undergoes a transition from second to first order phase transition by changing
only the finite range of the interaction.Comment: Soumis pour publication a Journal of statistical physics - version
r\'{e}vis\'{e}
Density Profiles in Molecular Cloud Cores Associated with High-Mass Star-Forming Regions
Radial density profiles for the sample of dense cores associated with
high-mass star-forming regions from southern hemisphere have been derived using
the data of observations in continuum at 250 GHz. Radial density profiles for
the inner regions of 16 cores (at distances \la 0.2-0.8 pc from the center)
are close on average to the dependence, where
. In the outer regions density drops steeper. An analysis
with various hydrostatic models showed that the modified Bonnor-Ebert model,
which describes turbulent sphere confined by external pressure, is preferable
compared with the logotrope and polytrope models practically in all cases. With
a help of the Bonnor-Ebert model, estimates of central density in a core,
non-thermal velocity dispersion and core size are obtained. The comparison of
central densities with the densities derived earlier from the CS modeling
reveals differences in several cases. The reasons of such differences are
probably connected with the presence of density inhomogenities on the scales
smaller than the telescope beam. In most cases non-thermal velocity dispersions
are in agreement with the values obtained from molecular line observations.Comment: 12 pages, 3 figures, 4 table
Molecular beam epitaxy of metamorphic buffer for InGaAs/InP photodetectors with high photosensitivity in the range of 2.2–2.6 um
The present work is concerned with finding optimal technological conditions for the synthesis of heterostructures with a metamorphic buffer for InGaAs/InP photodetectors in the wavelength range of 2.2–2.6 um using molecular beam epitaxy. Three choices of buffer structure differing in design and growth parameters were proposed.
The internal structure of the grown samples was investigated by X-ray diffraction and transmission electron microscopy. Experimental data analysis has shown that the greatest degree of elastic strain relaxation in the InGaAs active layer was achieved in the sample where the metamorphic buffer formation ended with a consecutive increase and decrease in temperature. The said buffer also had InAs/InAlAs superlattice inserts.
The dislocation density in this sample turned out to be minimal out of three, which allowed us to conclude that the described heterostructure configuration appears to be the most appropriate for manufacturing of short wavelength infrared range pin-photodetectors with high photosensitivity
Magnetic spin reorientation in Tb3Fe5O12 under external magnetic field
The research was carried out on HANARO reactor KAERI, and partially at IMP Neutron Material Science Complex within the state assignment of FASO of Russia (theme “Flux” No. 01201463334), supported in part by grant 15-8-2-2 of the Program of Fundamental Researches of UB RAS and by the State contract (No. 3.6121.2017) between UrFU and the Ministry of Education and Science of Russian Federation
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