1,855 research outputs found
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
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.
The first CO+ image: Probing the HI/H2 layer around the ultracompact HII region Mon R2
The CO+ reactive ion is thought to be a tracer of the boundary between a HII
region and the hot molecular gas. In this study, we present the spatial
distribution of the CO+ rotational emission toward the Mon R2 star-forming
region. The CO+ emission presents a clumpy ring-like morphology, arising from a
narrow dense layer around the HII region. We compare the CO+ distribution with
other species present in photon-dominated regions (PDR), such as [CII] 158 mm,
H2 S(3) rotational line at 9.3 mm, polycyclic aromatic hydrocarbons (PAHs) and
HCO+. We find that the CO+ emission is spatially coincident with the PAHs and
[CII] emission. This confirms that the CO+ emission arises from a narrow dense
layer of the HI/H2 interface. We have determined the CO+ fractional abundance,
relative to C+ toward three positions. The abundances range from 0.1 to
1.9x10^(-10) and are in good agreement with previous chemical model, which
predicts that the production of CO+ in PDRs only occurs in dense regions with
high UV fields. The CO+ linewidth is larger than those found in molecular gas
tracers, and their central velocity are blue-shifted with respect to the
molecular gas velocity. We interpret this as a hint that the CO+ is probing
photo-evaporating clump surfaces.Comment: The main text has 4 pages, 2 pages of Appendix, 4 figures, 1 table.
Accepted for publication in Astronomy and Astrophysics letter
Anaphylaxis related to avocado ingestion: a case and review
Anaphylaxis to avocado, independent of latex sensitization, has been rarely reported in the literature. This case report describes a 15 year old male who experienced anaphylaxis within half an hour after eating avocado-containing food. Avocado consumption is common in both North America and South America. It is important to consider avocado as a cause of anaphylaxis, even in patients not sensitized to latex
PRE-TREATMENT AND ENZYMATIC HYDROLYSIS OF BANANA (Musa acuminata x balbisiana) PSEUDOSTEM FOR ETHANOL PRODUCTION
Banana (M. acuminata x balbisiana) is an abundant lignocellulosic waste material in large plantations all over the Philippines, especially in Mindanao, which can be utilized as substrate in producing high-value products like ethanol. To compensate for the low yield based on total weight of substrate due to the high moisture content of banana pseudostem, there is the primary challenge to make the conversion of this lignocellulosic biomass into monomeric sugar and then into ethanol more efficiently in order to achieve yields that would make it cost-competitive. Hence, this study evaluated the effects of solid loading, incubation time and amount of enzyme on yield of reducing sugars in the enzymatic hydrolysis process and attempted to optimize the significant factors by Response Surface Methodology (RSM), specifically using Box-Behnken design. There was significant improvement on the reducing sugar yield of the pretreated banana pseudostem at 20 h incubation time, 15 g solid loading and 0.55 % enzyme concentration. Ethanol production was observed to be higher in the detoxified substrate although biomass was higher for the non-detoxified substrate. As to our knowledge, the present study is the first attempt to produce second generation ethanol using banana pseudostem waste as feedstock in the Philippines
Transfer of a major dominant gene for resistance to eyespot disease from a wild grass to hexaploid wheat
Eyespot disease, caused by the fungus Pseudocercosporella herpotrichoides, is responsible for considerable lodging and reductions of yield in extensive areas of wheat cultivation in North and South America, Europe, New Zealand, Australia and Africa1. The level of resistance of wheat cultivars is too low, even among the less susceptible ones (that is, Cappelle Desprez and Cerco) and no genes for resistance have to date been characterized in any species. Sprague2 found a high level of resistance to this disease in the wild grass Aegilops ventricosa and several workers have attempted its transfer to cultivated wheat with only partial success3â5. We report here a major dominant gene for resistance, which has been transferred from tetraploid Ae. ventricosa (genomes DvDvMvMv) to hexaploid wheat, Triticum aestivum (AABBDD), using tetraploid wheat, Triticum turgidum (AABB), as a 'bridge' species
Determination of pH in Regions of the Midguts of Acaridid Mites
The pH of the guts of mites strongly affects their digestive processes. This study was carried out to determine the pH in the guts of 12 species of stored product and house dust mites. Eighteen pH indicators were chosen and offered to the mites in the feeding biotest. Based on the color changes of the indicators, the gut contents of acaridid mites were determined to be within a pH range of 4 to neutral. The gut contents showed a gradient in pH from the anterior to the posterior part. The anterior midgut (ventriculus and caeca) of most species had a pH ranging from 4.5 to 5, or slightly more alkaline for most of the species, while the middle midgut (intercolon/colon) had a pH of 5 to 6. Finally, the pH of the posterior midgut (postcolon) was between 5.5 and 7. Except for Dermatophagoides spp., no remarkable differences in the pH of the gut were observed among the tested species. Dermatophagoides spp. had a more acidic anterior midgut (a pH of 4 to 5) and colon (a pH of 5) with postcolon (a pH of below 6). The results characterizing in vivo conditions in the mite gut offer useful information to study the activity of mite digestive enzymes including their inhibitors and gut microflora
Dense gas in IRAS 20343+4129: an ultracompact HII region caught in the act of creating a cavity
The intermediate- to high-mass star-forming region IRAS 20343+4129 is an
excellent laboratory to study the influence of high- and intermediate-mass
young stellar objects on nearby starless dense cores, and investigate for
possible implications in the clustered star formation process. We present 3 mm
observations of continuum and rotational transitions of several molecular
species (C2H, c-C3H2, N2H+, NH2D) obtained with the Combined Array for Research
in Millimetre-wave Astronomy, as well as 1.3 cm continuum and NH3 observations
carried out with the Very Large Array, to reveal the properties of the dense
gas. We confirm undoubtedly previous claims of an expanding cavity created by
an ultracompact HII region associated with a young B2 zero-age main sequence
(ZAMS) star. The dense gas surrounding the cavity is distributed in a filament
that seems squeezed in between the cavity and a collimated outflow associated
with an intermediate-mass protostar. We have identified 5 millimeter continuum
condensations in the filament. All of them show column densities consistent
with potentially being the birthplace of intermediate- to high-mass objects.
These cores appear different from those observed in low-mass clustered
environments in sereval observational aspects (kinematics, temperature,
chemical gradients), indicating a strong influence of the most massive and
evolved members of the protocluster. We suggest a possible scenario in which
the B2 ZAMS star driving the cavity has compressed the surrounding gas,
perturbed its properties and induced the star formation in its immediate
surroundings.Comment: 17 pages, 13 figures. Accepted for publication in Monthly Notices of
the Royal Astronomical Society (Main Journal
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