196 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 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
Molecular Emission in Dense Massive Clumps from the Star-Forming Regions S231-S235
The article deals with observations of star-forming regions S231-S235 in
'quasi-thermal' lines of ammonia (NH), cyanoacetylene (HCN) and maser
lines of methanol (CHOH) and water vapor (HO). S231-S235 regions is
situated in the giant molecular cloud G174+2.5. We selected all massive
molecular clumps in G174+2.5 using archive CO data. For the each clump we
determined mass, size and CO column density. After that we performed
observations of these clumps. We report about first detections of NH and
HCN lines toward the molecular clumps WB89 673 and WB89 668. This means
that high-density gas is present there. Physical parameters of molecular gas in
the clumps were estimated using the data on ammonia emission. We found that the
gas temperature and the hydrogen number density are in the ranges 16-30 K and
2.8-7.2 cm, respectively. The shock-tracing line of CHOH
molecule at 36.2 GHz is newly detected toward WB89 673.Comment: 16 pages, 4 figure
Astrochemical studies of molecular clouds in Orion
Цель лекции представить астрохимические исследования в молекулярных облаках Орион А и Орион В. Основное внимание будет уделено молекулярному облаку Orion Bar и туманности Конская голова.The aim of the lecture is to outline astrochemical studies of Orion A and Orion B molecular clouds. Main attention is given to the Orion Bar and Horsehead nebula.Работа выполнена при поддержке гранта РФФИ 16-02-00834 A
Molecular gas in high-mass filament WB673
We studied the distribution of dense gas in a filamentary molecular cloud
containing several dense clumps. The center of the filament is given by the
dense clump WB673. The clumps are high-mass and intermediate-mass star-forming
regions. We observed CS(2-1), 13CO(1-0), C18O(1-0) and methanol lines at 96GHz
toward WB673 with the Onsala Space Observatory 20-m telescope. We found CS(2-1)
emission in the inter-clump medium so the clumps are physically connected and
the whole cloud is indeed a filament. Its total mass is M and
mass-to-length ratio is 360 Mpc from 13CO(1-0) data.
Mass-to-length ratio for the dense gas is Mpc from
CS(2-1) data. The PV-diagram of the filament is V-shaped. We estimated physical
conditions in the molecular gas using methanol lines. Location of the filament
on the sky between extended shells suggests that it could be a good example to
test theoretical models of formation of the filaments via multiple compression
of interstellar gas by supersonic waves
Star formation timescale in the molecular filament WB 673
We present observations of ammonia emission lines toward the interstellar
filament WB~673 hosting the dense clumps WB~673, WB~668, S233-IR and
G173.57+2.43. LTE analysis of the lines allows us to estimate gas kinetic
temperature ( 30~K in all the clumps), number density
(~cm), and ammonia column density (~cm) in the dense clumps. We find signatures of collapse in WB
673 and presence of compact spatially unresolved dense clumps in S233-IR. We
reconstruct 1D density and temperature distributions in the clumps and estimate
their ages using astrochemical modelling. Considering CO, CS, NH and
NH molecules (plus HCN and HNC for WB~673), we find a chemical age of
~yrs providing the best agreement between the
simulated and observed column densities in all the clumps. Therefore, we
consider as the chemical age of the entire filament. A long
preceding low-density stage of gas accumulation in the astrochemical model
would break the agreement between the simulated and observed column densities.
We suggest that rapid star formation over a ~yrs timescale take
place in the filament.Comment: 10 pages, 7 figures, accepted for publication in MNRA
Infrared Morphology of Regions of Ionized Hydrogen
A search for infrared ring nebulae associated with regions of ionized
hydrogen has been carried out. The New GPS Very Large Array survey at 20 cm
forms the basis of the search, together with observations obtained with the
Spitzer Space Telescope at 8 and 24 m and the Herschel Space Telescope at
70 m. Objects having ring-like morphologies at 8 m and displaying
extended emission at 20 cm were selected visually. Emission at 24 m having
the form of an inner ring or central peak is also observed in the selected
objects. A catalog of 99 ring nebulae whose shapes at 8 and 70 m are well
approximated by ellipses has been compiled. The catalog contains 32 objects
whose shapes are close to circular (eccentricities of the fitted ellipses at 8
m no greater than 0.6, angular radius exceeding 20). These objects are
promising for comparisons with the results of one-dimensional hydrodynamical
simulations of expanding regions of ionized hydrogen.Comment: Astronomy Reports, Volume 61, Issue 12, pp.1015-1030 (ARep Homepage
Physical conditions in star-forming regions around s235
Gas density and temperature in star-forming regions around Sh2-235 are derived from ammonialine observations. This information is used to evaluate formation scenarios and to determineevolutionary stages of the young embedded clusters S235 East 1, S235 East 2 and S235 Central.We also estimate the gas mass in the embedded clusters and its ratio to the stellar mass.S235 East 1 appears to be less evolved than S235 East 2 and S235 Central. In S235 East 1 themolecular gas mass exceeds that in the other clusters. Also, this cluster is more embeddedin the parent gas cloud than the other two. Comparison with a theoretical model shows thatthe formation of these three clusters could have been stimulated by the expansion of theSh2-235 HII region (hereafter S235) via a collect-and-collapse process, provided the densityin the surrounding gas exceeds 3 × 103 cm-3, or via collapse of pre-existing clumps. Theexpansion of S235 cannot be responsible for star formation in the southern S235 A-B region.However, formation of the massive stars in this region might have been triggered by a largescalesupernova shock. Thus, triggered star formation in the studied region may come in threevarieties, namely collect-and-collapse and collapse of pre-existing clumps, both initiated byexpansion of the localHII regions, and triggered by an external large-scale shock.We argue thatthe S235A HII region expands into a highly non-uniform medium with increasing density. It istoo young to trigger star formation in its vicinity by a collect-and-collapse process. There is anage spread inside the S235 A-B region. Massive stars in the S235 A-B region are considerablyyounger than lower mass stars in the same area. This follows from the estimates of their agesand the ages of associated HII regions. © 2013 The Authors
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