1,876 research outputs found
Probing the massive star forming environment - a multiwavelength investigation of the filamentary IRDC G333.73+0.37
We present a multiwavelength study of the filamentary infrared dark cloud
(IRDC) G333.73+0.37. The region contains two distinct mid-infrared sources S1
and S2 connected by dark lanes of gas and dust. Cold dust emission from the
IRDC is detected at seven wavelength bands and we have identified 10 high
density clumps in the region. The physical properties of the clumps such as
temperature: 14.3-22.3 K and mass: 87-1530 M_sun are determined by fitting a
modified blackbody to the spectral energy distribution of each clump between
160 micron and 1.2 mm. The total mass of the IRDC is estimated to be $~4700
M_sun. The molecular line emission towards S1 reveals signatures of
protostellar activity. Low frequency radio emission at 1300 and 610 MHz is
detected towards S1 (shell-like) and S2 (compact morphology), confirming the
presence of newly formed massive stars in the IRDC. Photometric analysis of
near and mid-infrared point sources unveil the young stellar object population
associated with the cloud. Fragmentation analysis indicates that the filament
is supercritical. We observe a velocity gradient along the filament, that is
likely to be associated with accretion flows within the filament rather than
rotation. Based on various age estimates obtained for objects in different
evolutionary stages, we attempt to set a limit to the current age of this
cloud.Comment: 26 pages, 20 figures, accepted by Ap
Evolution and excitation conditions of outflows in high-mass star-forming regions
Theoretical models suggest that massive stars form via disk-mediated
accretion, with bipolar outflows playing a fundamental role. A recent study
toward massive molecular outflows has revealed a decrease of the SiO line
intensity as the object evolves. The present study aims at characterizing the
variation of the molecular outflow properties with time, and at studying the
SiO excitation conditions in outflows associated with massive YSOs. We used the
IRAM30m telescope to map 14 massive star-forming regions in the SiO(2-1),
SiO(5-4) and HCO+(1-0) outflow lines, and in several dense gas and hot core
tracers. Hi-GAL data was used to improve the spectral energy distributions and
the L/M ratio, which is believed to be a good indicator of the evolutionary
stage of the YSO. We detect SiO and HCO+ outflow emission in all the sources,
and bipolar structures in six of them. The outflow parameters are similar to
those found toward other massive YSOs. We find an increase of the HCO+ outflow
energetics as the object evolve, and a decrease of the SiO abundance with time,
from 10^(-8) to 10^(-9). The SiO(5-4) to (2-1) line ratio is found to be low at
the ambient gas velocity, and increases as we move to high velocities,
indicating that the excitation conditions of the SiO change with the velocity
of the gas (with larger densities and/or temperatures for the high-velocity gas
component). The properties of the SiO and HCO+ outflow emission suggest a
scenario in which SiO is largely enhanced in the first evolutionary stages,
probably due to strong shocks produced by the protostellar jet. As the object
evolves, the power of the jet would decrease and so does the SiO abundance.
During this process, however, the material surrounding the protostar would have
been been swept up by the jet, and the outflow activity, traced by entrained
molecular material (HCO+), would increase with time.Comment: 31 pages, 10 figures and 5 tables (plus 2 figures and 3 tables in the
appendix). Accepted for publication in A&A. [Abstract modified to fit the
arXiv requirements.
Physical properties of high-mass clumps in different stages of evolution
(Abridged) Aims. To investigate the first stages of the process of high-mass
star formation, we selected a sample of massive clumps previously observed with
the SEST at 1.2 mm and with the ATNF ATCA at 1.3 cm. We want to characterize
the physical conditions in such sources, and test whether their properties
depend on the evolutionary stage of the clump.
Methods. With ATCA we observed the selected sources in the NH3(1,1) and (2,2)
transitions and in the 22 GHz H2O maser line. Ammonia lines are a good
temperature probe that allow us to accurately determine the mass and the
column-, volume-, and surface densities of the clumps. We also collected all
data available to construct the spectral energy distribution of the individual
clumps and to determine if star formation is already occurring, through
observations of its most common signposts, thus putting constraints on the
evolutionary stage of the source. We fitted the spectral energy distribution
between 1.2 mm and 70 microns with a modified black body to derive the dust
temperature and independently determine the mass.
Results. The clumps are cold (T~10-30 K), massive (M~10^2-10^3 Mo), and dense
(n(H2)>~10^5 cm^-3) and they have high column densities (N(H2)~10^23 cm^-2).
All clumps appear to be potentially able to form high-mass stars. The most
massive clumps appear to be gravitationally unstable, if the only sources of
support against collapse are turbulence and thermal pressure, which possibly
indicates that the magnetic field is important in stabilizing them.
Conclusions. After investigating how the average properties depend on the
evolutionary phase of the source, we find that the temperature and central
density progressively increase with time. Sources likely hosting a ZAMS star
show a steeper radial dependence of the volume density and tend to be more
compact than starless clumps.Comment: Published in A&A, Vol. 556, A1
Thermal Jeans fragmentation within 1000 AU in OMC-1S
We present subarcsecond 1.3 mm continuum ALMA observations towards the Orion
Molecular Cloud 1 South (OMC-1S) region, down to a spatial resolution of 74 AU,
which reveal a total of 31 continuum sources. We also present subarcsecond 7 mm
continuum VLA observations of the same region, which allow to further study
fragmentation down to a spatial resolution of 40 AU. By applying a Mean Surface
Density of Companions method we find a characteristic spatial scale at ~560 AU,
and we use this spatial scale to define the boundary of 19 `cores' in OMC-1S as
groupings of millimeter sources. We find an additional characteristic spatial
scale at ~2900 AU, which is the typical scale of the filaments in OMC-1S,
suggesting a two-level fragmentation process. We measured the fragmentation
level within each core and find a higher fragmentation towards the southern
filament. In addition, the cores of the southern filament are also the densest
(within 1100 AU) cores in OMC-1S. This is fully consistent with previous
studies of fragmentation at spatial scales one order of magnitude larger, and
suggests that fragmentation down to 40 AU seems to be governed by thermal Jeans
processes in OMC-1S.Comment: Accepted to Ap
Synthesis of quinoxaline 1,4-di-N-oxide derivatives on solid support using room temperature and microwave-assisted solvent-free procedures
We describe the synthesis of 12 new ethyl and methyl quinoxaline-7-carboxylate 1,4-di-N-oxide derivatives on solid supports with room temperature and microwave-assisted solvent-free procedures. Results show that solid supports have good catalytic activity in the formation of quinoxaline 1,4-di-N-oxide derivatives. We found that florisil and montmorillonite KSF and K10 could be used as new, easily available, inexpensive alternatives of catalysts. Additionally, room temperature and microwave-irradiation solvent-free synthesis was more efficient than a conventional procedure (Beirut reaction), reducing reaction time and increasing yield
Deuteration and evolution in the massive star formation process: the role of surface chemistry
An ever growing number of observational and theoretical evidence suggests
that the deuterated fraction (column density ratio between a species containing
D and its hydrogenated counterpart, Dfrac) is an evolutionary indicator both in
the low- and the high-mass star formation process. However, the role of surface
chemistry in these studies has not been quantified from an observational point
of view. In order to compare how the deuterated fractions of species formed
only in the gas and partially or uniquely on grain surfaces evolve with time,
we observed rotational transitions of CH3OH, 13CH3OH, CH2DOH, CH3OD at 3 and
1.3~mm, and of NH2D at 3~mm with the IRAM-30m telescope, and the inversion
transitions (1,1) and (2,2) of NH3 with the GBT, towards most of the cores
already observed by Fontani et al.~(2011, 2014) in N2H+, N2D+, HNC, DNC. NH2D
is detected in all but two cores, regardless of the evolutionary stage.
Dfrac(NH3) is on average above 0.1, and does not change significantly from the
earliest to the most evolved phases, although the highest average value is
found in the protostellar phase (~0.3). Few lines of CH2DOH and CH3OD are
clearly detected, and only towards protostellar cores or externally heated
starless cores. This work clearly confirms an expected different evolutionary
trend of the species formed exclusively in the gas (N2D+ and N2H+) and those
formed partially (NH2D and NH3) or totally (CH2DOH and CH3OH) on grain mantles.
The study also reinforces the idea that Dfrac(N2H+) is the best tracer of
massive starless cores, while high values of Dfrac(CH3OH) seem rather good
tracers of the early protostellar phases, at which the evaporation/sputtering
of the grain mantles is most efficient.Comment: 14 pages, 7 figures, 2 Appendice
Gravity or turbulence? -III. Evidence of pure thermal Jeans fragmentation at ~0.1 pc scale
We combine previously published interferometric and single-dish data of
relatively nearby massive dense cores that are actively forming stars to test
whether their `fragmentation level' is controlled by turbulent or thermal
support. We find no clear correlation between the fragmentation level and
velocity dispersion, nor between the observed number of fragments and the
number of fragments expected when the gravitationally unstable mass is
calculated including various prescriptions for `turbulent support'. On the
other hand, the best correlation is found for the case of pure thermal Jeans
fragmentation, for which we infer a core formation efficiency around 13 per
cent, consistent with previous works. We conclude that the dominant factor
determining the fragmentation level of star-forming massive dense cores at 0.1
pc scale seems to be thermal Jeans fragmentation.Comment: accepted in MNRA
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