3,549 research outputs found
Gas kinematics in massive star-forming regions from the Perseus spiral arm
We present results of a survey of 14 star-forming regions from the Perseus
spiral arm in CS(2-1) and 13CO(1-0) lines with the Onsala Space Observatory 20
m telescope. Maps of 10 sources in both lines were obtained. For the remaining
sources a map in just one line or a single-point spectrum were obtained. On the
basis of newly obtained and published observational data we consider the
relation between velocities of the "quasi-thermal" CS(2-1) line and 6.7 GHz
methanol maser line in 24 high-mass star-forming regions in the Perseus arm. We
show that, surprisingly, velocity ranges of 6.7 GHz methanol maser emission are
predominantly red-shifted with respect to corresponding CS(2-1) line velocity
ranges in the Perseus arm. We suggest that the predominance of the "red-shifted
masers" in the Perseus arm could be related to the alignment of gas flows
caused by the large-scale motions in the Galaxy. Large-scale galactic shock
related to the spiral structure is supposed to affect the local kinematics of
the star-forming regions. Part of the Perseus arm, between galactic longitudes
from 85deg to 124deg, does not contain blue-shifted masers at all. Radial
velocities of the sources are the greatest in this particular part of the arm,
so the velocity difference is clearly pronounced. 13CO(1-0) and CS(2-1)
velocity maps of G183.35-0.58 show gas velocity difference between the center
and the periphery of the molecular clump up to 1.2 km/s. Similar situation is
likely to occur in G85.40-0.00. This can correspond to the case when the
large-scale shock wave entrains the outer parts of a molecular clump in motion
while the dense central clump is less affected by the shock.Comment: accepted by Astronomy Report
The Remarkable Mid-Infrared Jet of Massive Young Stellar Object G35.20-0.74
The young massive stellar object G35.20-0.74 was observed in the mid-infrared
using T-ReCS on Gemini South. Previous observations have shown that the near
infrared emission has a fan-like morphology that is consistent with emission
from the northern lobe of a bipolar radio jet known to be associated with this
source. Mid-infrared observations presented in this paper show a monopolar
jet-like morphology as well, and it is argued that the mid-infrared emission
observed is dominated by thermal continuum emission from dust. The mid-infrared
emission nearest the central stellar source is believed to be directly heated
dust on the walls of the outflow cavity. The hydroxyl, water, and methanol
masers associated with G35.20-0.74 are spatially located along these
mid-infrared cavity walls. Narrow jet or outflow cavities such as this may also
be the locations of the linear distribution of methanol masers that are found
associated with massive young stellar objects. The fact that G35.20-0.74 has
mid-infrared emission that is dominated by the outflow, rather than disk
emission, is a caution to those that consider mid-infrared emission from young
stellar objects as only coming from circumstellar disks.Comment: Accepted for publication in ApJ Letters; 4 pages; 2 figures; a
version with full resolution images is available here:
http://www.ctio.noao.edu/~debuizer
On the Class II Methanol Maser Periodic Variability due to the Rotating Spiral Shocks in the Gaps of Disks Around Young Binary Stars
We argue that the periodic variability of Class II methanol masers can be
explained by variations of the dust temperature in the accretion disk around
proto-binary star with at least one massive component. The dust temperature
variations are caused by rotation of hot and dense material of the spiral shock
wave in the disk central gap. The aim of this work is to show how different can
be the Class II methanol maser brightness in the disk during the Moment of
Maximum Illumination by the Spiral Shock material (hereafter MMISS) and the
Moment when the disk is Illuminated by the Stars Only (MISO). We used the code
CLOUDY (v13.02) to estimate physical conditions in the flat disk in the MISO
and the MMISS. Model physical parameters of the disk were then used to estimate
the brightness of 6.7, 9.9, 12.1 and 107 GHz masers at different impact
parameters using LVG approximation. It was shown that the strong masers
experience considerable brightness increase during the MMISS with respect to
MISO. There can happen both flares and dips of the 107 GHz maser brightness
under the MMISS conditions, depending on the properties of the system. The
brightest 9.9 GHz masers in the MMISS are situated at the greater than the
strong 6.7, 12.1 and 107 GHz masers that are situated at AU. The
brightness of 9.9 GHz maser in the MMISS suppressed at AU and increase
at AU.Comment: Accepted for publication in MNRAS, 9 figure
Schr\"odinger operator on homogeneous metric trees: spectrum in gaps
The paper studies the spectral properties of the Schr\"odinger operator
on a homogeneous rooted metric tree, with a decaying
real-valued potential and a coupling constant . The spectrum of the
free Laplacian has a band-gap structure with a single
eigenvalue of infinite multiplicity in the middle of each finite gap. The
perturbation gives rise to extra eigenvalues in the gaps. These
eigenvalues are monotone functions of if the potential has a fixed
sign. Assuming that the latter condition is satisfied and that is
symmetric, i.e. depends on the distance to the root of the tree, we carry out a
detailed asymptotic analysis of the counting function of the discrete
eigenvalues in the limit . Depending on the sign and decay of ,
this asymptotics is either of the Weyl type or is completely determined by the
behaviour of at infinity.Comment: AMS LaTex file, 47 page
The Spectral Type of the Ionizing Stars and the Infrared Fluxes of HII Regions
The 20 cm radio continuum fluxes of 91 HII regions in a previously compiled
catalog have been determined. The spectral types of the ionizing stars in 42
regions with known distances are estimated. These spectral types range from
B0.5 to O7, corresponding to effective temperatures of 29 000-37 000 K. The
dependences of the infrared (IR) fluxes at 8, 24, and 160 m on the 20 cm
flux are considered. The IR fluxes are used as a diagnostic of heating of the
matter, and the radio fluxes as measurements of the number of ionizing photons.
It is established that the IR fluxes grow approximately linearly with the radio
flux. This growth of the IR fluxes probably indicates a growth of the mass of
heated material in the envelope surrounding the HII region with increasing
effective temperature of the star.Comment: 16, pages, 10 figures, published in Astronomy Report
MECHANISM OF THICK METAL WALLS PENETRATION BY HIGH-SPEED MICROPARTICLES
Purpose. Analysis and estimation of physical parameters which create conditions for microparticles penetration into metal microstructure to abnormally big depth.
Methodology. Quantum mechanical threesite model has been used for studying the regularities of electron motion in the field of two Coulomb centres and numerical solution for the problem of the effect of external electrical charge on stability of the chemical bond. Solution was found for the equation of heat conductivity for estimating the temperature of microparticles heating under compression and acceleration by explosively driven accelerator. Stokes’s law was used for estimating viscosity of hypothetical medium which can be penetrated by microparticle at a great speed and to a great depth. The research was done with the help of Xray microanalysis, Xray crystallography, micrographic investigation, massspectrometry and electronic spectroscopy.
Findings. Solution of the quantum mechanical model testifies that electric charges serve as catalysts responsible for the significant reduction of the energy barrier of chemical reactions. To ensure super deep penetration, it is necessary to achieve acceleration of a great number of microparticles in a special explosively driven accelerator. Heating, intensive stirring and friction result in electrification of the surface of the particles, which is known as triboelectric effect. The hypothesis about physical and chemical mechanism of particles penetration into metals resulting from highspeed impact has been put forward.
Originality. The research has established relationship between the sizes of microparticles accelerated by
explosion and the density of electric charges on their surfaces, as well as the depth of their penetration into the metal barrier. By experimental research, it was proven that maximum depth of microparticles penetration is directly proportional to the maximum density of surface charges for the particles of the 50…80 µm size. It is assumed that particles penetration into metals to greater depths is conditioned by the reduction of the barrier material viscosity in the zone of particlebarrier contact due to quantum mechanical effects in the solidstate plasma.
Practical value. The value of the work includes creating a new generation of metal composites as well as new prospective technologies of reactive materials utilization
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