259 research outputs found
The dynamical properties of dense filaments in the infrared dark cloud G035.39-00.33
Infrared Dark Clouds (IRDCs) are unique laboratories to study the initial
conditions of high-mass star and star cluster formation. We present
high-sensitivity and high-angular resolution IRAM PdBI observations of N2H+
(1-0) towards IRDC G035.39-00.33. It is found that G035.39-00.33 is a highly
complex environment, consisting of several mildly supersonic filaments
(sigma_NT/c_s ~1.5), separated in velocity by <1 km s^-1 . Where multiple
spectral components are evident, moment analysis overestimates the non-thermal
contribution to the line-width by a factor ~2. Large-scale velocity gradients
evident in previous single-dish maps may be explained by the presence of
substructure now evident in the interferometric maps. Whilst global velocity
gradients are small (<0.7 km s^-1 pc^-1), there is evidence for dynamic
processes on local scales (~1.5-2.5 km s^-1 pc^-1 ). Systematic trends in
velocity gradient are observed towards several continuum peaks. This suggests
that the kinematics are influenced by dense (and in some cases, starless)
cores. These trends are interpreted as either infalling material, with
accretion rates ~(7 \pm 4)x10^-5 M_sun yr^-1 , or expanding shells with
momentum ~24 \pm 12 M_sun km s^-1 . These observations highlight the importance
of high-sensitivity and high-spectral resolution data in disentangling the
complex kinematic and physical structure of massive star forming regions.Comment: 25 pages, 23 figures, accepted for publication in MNRA
Strategy and criteria to optically design a solar concentration plant
AbstractThe objective of this work is to individuate the best strategy to determine the layout of a thermodynamic plant based on the concentration of solar flux by means of a large number of mirrors. Many software tools exist, both dedicated software and more general optical software. This analysis shows the advantages derived from the use of a general non-sequential optical software, proposing criteria and procedures in order to establish dedicated optical merit figures, which are suggested and evaluated from the point of view of their effectiveness to achieve a favorable layout design. Particular attention is devoted to merit figures that estimate the optical efficiency, a key quantity for all the CSP plants that can be defined in different ways. The description includes examples of application, discussion of results and various proposed alternatives for the merit figure
Gas Kinematics and Excitation in the Filamentary IRDC G035.39-00.33
Some theories of dense molecular cloud formation involve dynamical
environments driven by converging atomic flows or collisions between
preexisting molecular clouds. The determination of the dynamics and physical
conditions of the gas in clouds at the early stages of their evolution is
essential to establish the dynamical imprints of such collisions, and to infer
the processes involved in their formation. We present multi-transition 13CO and
C18O maps toward the IRDC G035.39-00.33, believed to be at the earliest stages
of evolution. The 13CO and C18O gas is distributed in three filaments
(Filaments 1, 2 and 3), where the most massive cores are preferentially found
at the intersecting regions between them. The filaments have a similar
kinematic structure with smooth velocity gradients of ~0.4-0.8 km s-1 pc-1.
Several scenarios are proposed to explain these gradients, including cloud
rotation, gas accretion along the filaments, global gravitational collapse, and
unresolved sub-filament structures. These results are complemented by HCO+,
HNC, H13CO+ and HN13C single-pointing data to search for gas infall signatures.
The 13CO and C18O gas motions are supersonic across G035.39-00.33, with the
emission showing broader linewidths toward the edges of the IRDC. This could be
due to energy dissipation at the densest regions in the cloud. The average H2
densities are ~5000-7000 cm-3, with Filaments 2 and 3 being denser and more
massive than Filament 1. The C18O data unveils three regions with high CO
depletion factors (f_D~5-12), similar to those found in massive starless cores.Comment: 20 pages, 14 figures, 6 tables, accepted for publication in MNRA
Mid-J CO Shock Tracing Observations of Infrared Dark Clouds I
Infrared dark clouds (IRDCs) are dense, molecular structures in the
interstellar medium that can harbour sites of high-mass star formation. IRDCs
contain supersonic turbulence, which is expected to generate shocks that
locally heat pockets of gas within the clouds. We present observations of the
CO J = 8-7, 9-8, and 10-9 transitions, taken with the Herschel Space
Observatory, towards four dense, starless clumps within IRDCs (C1 in
G028.37+00.07, F1 and F2 in G034.43+0007, and G2 in G034.77-0.55). We detect
the CO J = 8-7 and 9-8 transitions towards three of the clumps (C1, F1, and F2)
at intensity levels greater than expected from photodissociation region (PDR)
models. The average ratio of the 8-7 to 9-8 lines is also found to be between
1.6 and 2.6 in the three clumps with detections, significantly smaller than
expected from PDR models. These low line ratios and large line intensities
strongly suggest that the C1, F1, and F2 clumps contain a hot gas component not
accounted for by standard PDR models. Such a hot gas component could be
generated by turbulence dissipating in low velocity shocks.Comment: 14 pages, 8 figures, 5 tables, accepted by A&A, minor updates to
match the final published versio
IRAS 23385+6053: a candidate protostellar massive object
We present the results of a multi-line and continuum study towards the source
IRAS 23385+6053,performed with the IRAM-30m telescope, the Plateau de Bure
Interferometer, the Very Large Array Interferometer and the James Clerk Maxwell
Telescope. The new results confirm our earlier findings, namely that IRAS
23385+6053 is a good candidate high-mass protostellar object, precursor of an
ultracompact H region. The source is roughly composed of two regions: a
molecular core pc in size, with a temperature of K
and an H volume density of the order of 10 cm, and an
extended halo of diameter 0.4 pc, with an average kinetic temperature of
K and H volume density of the order of 10 cm. The
core temperature is much smaller than what is typically found in molecular
cores of the same diameter surrounding massive ZAMS stars. We deduce that the
core luminosity is between 150 and , and we believe
that the upper limit is near the ``true'' source luminosity. Moreover, by
comparing the H volume density obtained at different radii from the IRAS
source, we find that the halo has a density profile of the type . This suggests that the source is gravitationally
unstable. Finally, we demonstrate that the temperature at the core surface is
consistent with a core luminosity of and conclude that we
might be observing a protostar still accreting material from its parental
cloud, whose mass at present is .Comment: 18 pages, 20 figure
Mirror Surface Check on Solar Troughs by Optical Profilometry
Abstract Linear parabolic collectors usually need profilometric control since the reflector surface can be imperfectly manufactured. Optical profile assessment is generally addressed to detect small localised defects. The paper proposes two optical devices that were developed simulating profile measurements on linear parabolic mirrors. Solar troughs are employed in thermal plants and concentrating photovoltaic systems. The profilometer examines the reflector surface operating on a plane transversal to the linear axis of the trough collector. Then the detection is repeated displacing the optical device along the linear collector axis. The first profilometer includes a shifted laser source and a target placed at the collector focal distance. The second profilometer has a fixed target and a linear laser source, which is approximately located in the focal position of the solar mirror. Ray-tracing simulations and practical tests are illustrated for both optical devices
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