1,207 research outputs found
Description of Bocchus irwini sp. nov. from Madagascar (Hymenoptera Dryinidae)
Bocchus irwini sp. nov. is described from a male collected in Analagnambe forest,
Mahajanga Province, Madagascar. The new species is similar to Bocchus watshami Olmi 1987.
Keys to the Afrotropical species of Bocchus are modified to include the new species
Two new species of Dryinidae (Hymenoptera: Chrysidoidea) from areas of Atlantic Rainforest at São Paulo State, Brazil
Description of Anteon seramense (Hymenoptera. Dryinidae), a new species from Indonesia
Anteon seramense sp. nov. is described from Seram Island (Indonesia). Seram is an island
situated in a transition area between the Oriental and the Australian regions. Anteon seramense
can be distinguished from the related Australian species A. giluwense Olmi and
A. chelogynoides (Perkins) by the different sculpture of the scutum (granulated in A. seramense,
punctate and unsculptured among punctures in A. giluwense and A. chelogynoides)
and the different distal apex of the protarsal segment 5 (deeply hollow in A. seramense,
not hollow in A. giluwense and A. chelogynoides). Anteon seramense sp. nov. can be distinguished
from the related Oriental species A. heppneri Olmi and A. thai Olmi by the different
shape of the protarsal segment 5 (basal part slightly longer than distal part in A. seramense,
much longer in A. heppneri and A. thai)
Herschel-HIFI observations of H2O, NH3 and N2H+ toward high-mass starless and proto-stellar clumps identified by the Hi-GAL survey
Our present understanding of high-mass star formation still remains very
schematic. In particular, it is not yet clear how much of the difference
between low-mass and high-mass star formation occurs during the earliest star
formation phases. The chemical characteristics of massive cold clumps, and the
comparison with those of their low-mass counterparts, could provide crucial
clues about the exact role that chemistry plays in differentiating the early
phases of low-mass and high-mass star formation. Water, in particular, is a
unique probe of physical and chemical conditions in star-forming regions. Using
the HIFI instrument of Herschel we have observed the ortho-NH3 (1_0-0_0)
(572GHz), ortho-H2O (1_10-1_01) (557GHz) and N2H+ (6-5) (559GHz) lines toward a
sample of high-mass starless and proto-stellar clumps selected from the
"Herschel} Infrared Galactic Plane Survey" (Hi-GAL). We compare our results to
previous studies of low-mass and high-mass proto-stellar objects. At least one
of the three molecular lines was detected in 4 (out of 35) and 7 (out of 17)
objects in the l=59deg and l=30deg galactic regions, respectively. All detected
sources are proto-stellar. The water spectra are complex and consist of several
kinematic components, identified through a Gaussian decomposition, and in a few
sources inverse and regular P-Cygni profiles have been detected. All water line
profiles of the l=59deg region are dominated by a broad Gaussian emission
feature, indicating that the bulk of the water emission arises in outflows. No
such broad emission is detected toward the l=30deg objects. The ammonia line in
some cases also shows line wings and an inverse P-Cygni profile, thus
confirming that NH3 rotational transitions can be used to probe the dynamics of
high-mass star forming regions. Both bolometric and water line luminosity
increase with the continuum temperature.Comment: This paper includes 7 main figures and 6 tables, in addition to the
figures with the spectra of the individual sources which are presented as
on-line material. Accepted for publication on Astronomy and Astrophysic
The segregation of starless and protostellar clumps in the Hi-GAL l=224deg region
Stars form in dense, dusty structures, which are embedded in larger clumps of
molecular clouds often showing a clear filamentary structure on large scales (>
1pc). One of the best-studied regions in the Hi-GAL survey can be observed
toward the l=224deg field. Here, a filamentary region has been studied and it
has been found that protostellar clumps are mostly located along the main
filament, whereas starless clumps are detected off this filament and are
instead found on secondary, less prominent filaments. We want to investigate
this segregation effect and how it may affect the clumps properties. We mapped
the 12CO(1-0) line and its main three isotopologues toward the two most
prominent filaments observed toward the l=224deg field using the Mopra radio
telescope, in order to set observational constraints on the dynamics of these
structures and the associated starless and protostellar clumps. Compared to the
starless clumps, the protostellar clumps are more luminous, more turbulent and
lie in regions where the filamentary ambient gas shows larger linewidths. We
see evidence of gas flowing along the main filament, but we do not find any
signs of accretion flow from the filament onto the Hi-GAL clumps. We analyze
the radial column density profile of the filaments and their gravitational
stability. The more massive and highly fragmented main filament appears to be
thermally supercritical and gravitationally bound, assuming that all of the
non-thermal motion is contributing thermal-like support, suggesting a later
stage of evolution compared to the secondary filament. The status and
evolutionary phase of the Hi-GAL clumps would then appear to correlate with
that of the host filament.Comment: Accepted for publication on "Astronomy and Astrophysics
Herschel-HIFI observations of H2O, NH3, and N2H+ toward high-mass starless and protostellar clumps identified by the Hi-GAL survey
Context. Our present understanding of high-mass star formation still remains very schematic. In particular, it is not yet clear how much of the difference between low-mass and high-mass star formation occurs during the earliest star formation phases.
Aims. The chemical characteristics of massive cold clumps, and the comparison with those of their low-mass counterparts, could provide crucial clues about the exact role that chemistry plays in differentiating the early phases of low-mass and high-mass star formation. Water, in particular, is a unique probe of physical and chemical conditions in star-forming regions.
Methods. Using the HIFI instrument of Herschel, we have observed the ortho−NH3 (10 −00 ) (572 GHz), ortho−H2 O (110 −101 ) (557 GHz), and N2 H+ (6−5) (559 GHz) lines toward a sample of high-mass starless and protostellar clumps selected from the Herschel Infrared Galactic Plane Survey (Hi-GAL). We compare our results to previous studies of low-mass and high-mass protostellar objects. Results. At least one of the three molecular lines was detected in 4 (out of 35) and 7 (out of 17) objects in the l = 59° and l = 30° galactic regions, respectively. All detected sources are protostellar. The water spectra are complex and consist of several kinematic components, identified through a Gaussian decomposition, and we detected inverse and regular P-Cygni profiles in a few sources. All water line profiles of the l = 59° region are dominated by a broad Gaussian emission feature, indicating that the bulk of the water emission arises in outflows. No such broad emission is detected toward the l = 30° objects. The ammonia line in some cases also shows line wings and an inverse P-Cygni profile, thus confirming that NH3 rotational transitions can be used to probe the dynamics of high-mass, star-forming regions. Both bolometric and water line luminosity increase with the continuum temperature.
Conclusions. The higher water abundance toward the l = 59° sources, characterized by the presence of outflows and shocks, supports a scenario in which the abundance of this molecule is linked to the shocked gas. Various indicators suggest that the detected sources toward the l = 30° region are in a somewhat later evolutionary phase compared to the l = 59° field, although a firm conclusion is limited by the small number of observed sources. We find many similarities with studies carried out toward low-mass protostellar objects, but there are indications that the level of infall and turbulence in the high-mass protostars studied here could be significantly higher
Rotating disks in high-mass young stellar objects
We report on the detection of four rotating massive disks in two regions of
high-mass star formation. The disks are perpendicular to known bipolar outflows
and turn out to be unstable but long lived. We infer that accretion onto the
embedded (proto)stars must proceed through the disks with rates of ~10E-2
Msun/yr.Comment: 11 pages, 2 figures, 1 table; accepted for publication by ApJ
On the shape of the mass-function of dense clumps in the Hi-GAL fields. II. Using Bayesian inference to study the clump mass function
Context. Stars form in dense, dusty clumps of molecular clouds, but little is
known about their origin, their evolution and their detailed physical
properties. In particular, the relationship between the mass distribution of
these clumps (also known as the "clump mass function", or CMF) and the stellar
initial mass function (IMF), is still poorly understood. Aims. In order to
better understand how the CMF evolve toward the IMF, and to discern the "true"
shape of the CMF, large samples of bona-fide pre- and proto-stellar clumps are
required. Two such datasets obtained from the Herschel infrared GALactic Plane
Survey (Hi-GAL) have been described in paper I. Robust statistical methods are
needed in order to infer the parameters describing the models used to fit the
CMF, and to compare the competing models themselves. Methods. In this paper we
apply Bayesian inference to the analysis of the CMF of the two regions
discussed in Paper I. First, we determine the Bayesian posterior probability
distribution for each of the fitted parameters. Then, we carry out a
quantitative comparison of the models used to fit the CMF. Results. We have
compared the results from several methods implementing Bayesian inference, and
we have also analyzed the impact of the choice of priors and the influence of
various constraints on the statistical conclusions for the preferred values of
the parameters. We find that both parameter estimation and model comparison
depend on the choice of parameter priors. Conclusions. Our results confirm our
earlier conclusion that the CMFs of the two Hi-GAL regions studied here have
very similar shapes but different mass scales. Furthermore, the lognormal model
appears to better describe the CMF measured in the two Hi-GAL regions studied
here. However, this preliminary conclusion is dependent on the choice of
parameters priors.Comment: Submitted for publication to A&A on November 12, 2013. This paper
contains 11 pages and 7 figure
A spectral line survey of the starless and proto-stellar cores detected by BLAST toward the Vela-D molecular cloud
We present a 3-mm and 1.3-cm spectral line survey conducted with the Mopra
22-m and Parkes 64-m radio telescopes of a sample of 40 cold dust cores,
previously observed with BLAST, including both starless and proto-stellar
sources. 20 objects were also mapped using molecular tracers of dense gas. To
trace the dense gas we used the molecular species NH3, N2H+, HNC, HCO+, H13CO+,
HCN and H13CN, where some of them trace the more quiescent gas, while others
are sensitive to more dynamical processes. The selected cores have a wide
variety of morphological types and also show physical and chemical variations,
which may be associated to different evolutionary phases. We find evidence of
systematic motions in both starless and proto-stellar cores and we detect line
wings in many of the proto-stellar cores. Our observations probe linear
distances in the sources >~0.1pc, and are thus sensitive mainly to molecular
gas in the envelope of the cores. In this region we do find that, for example,
the radial profile of the N2H+(1-0) emission falls off more quickly than that
of C-bearing molecules such as HNC(1-0), HCO+(1-0) and HCN(1-0). We also
analyze the correlation between several physical and chemical parameters and
the dynamics of the cores. Depending on the assumptions made to estimate the
virial mass, we find that many starless cores have masses below the
self-gravitating threshold, whereas most of the proto-stellar cores have masses
which are near or above the self-gravitating critical value. An analysis of the
median properties of the starless and proto-stellar cores suggests that the
transition from the pre- to the proto-stellar phase is relatively fast, leaving
the core envelopes with almost unchanged physical parameters.Comment: Submitted for publication to Astronomy & Astrophysics on January
18th, 201
Mechanical characterization of parts fabricated by additive manufacturing
The explosion in the numbers of industrial applications making use of additive manufacturing (AM) techniques requires the use of reliable experimental data and appropriate design methods in order to ensure the adequate performance and safety of newly designed AM components. This Special Issue represents a collection of both experimental end numerical studies, covering the two realms of metallic and polymeric materials. The Special Issue is completed by papers focused on design and optimization problems, and on repair as well as on cost issues related to the production of AM components, which provide useful guidelines for design engineers and researchers
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