1,054 research outputs found
High mass star formation in the infrared dark cloud G11.11-0.12
We report detection of moderate to high-mass star formation in an infrared
dark cloud (G11.11-0.12) where we discovered class II methanol and water maser
emissions at 6.7 GHz and 22.2 GHz, respectively. We also observed the object in
ammonia inversion transitions. Strong emission from the (3,3) line indicates a
hot (~60 K) compact component associated with the maser emission. The line
width of the hot component (4 km/s), as well as the methanol maser detection,
are indicative of high mass star formation. To further constrain the physical
parameters of the source, we derived the spectral energy distribution (SED) of
the dust continuum by analysing data from the 2MASS survey, HIRAS, MSX, the
Spitzer Space Telescope, and interferometric 3mm observations. The SED was
modelled in a radiative transfer program: a) the stellar luminosity equals 1200
L_sun corresponding to a ZAMS star of 8 M_sun; b) the bulk of the envelope has
a temperature of 19 K; c) the mass of the remnant protostellar cloud in an area
8x10^17 cm or 15 arcsec across amounts to 500M_sun, if assuming standard dust
of the diffuse medium, and to about 60 M_sun, should the grains be fluffy and
have ice mantles; d) the corresponding visual extinction towards the star is a
few hundred magnitudes. The near IR data can be explained by scattering from
tenuous material above a hypothetical disk. The class II methanol maser lines
are spread out in velocity over 11 km/s. To explain the kinematics of the
masing spots, we propose that they are located in a Kepler disk at a distance
of about 250 AU. The dust temperatures there are around 150 K, high enough to
evaporate methanol--containing ice mantles.Comment: 10 pages, 6 figures, Accepted for publication in Astronomy &
Astrophysics Journa
Design and Development of a New Diagnostic Microbiology and Epidemiology Track in the General Meeting of the American Society for Microbiology
Spectral Energy Distributions of 6.7 GHz methanol masers
The 6.7 GHz maser transition of methanol has been found exclusively towards
massive star forming regions. A majority of the masers have been found to lack
the presence of any associated radio continuum. This could be due to the maser
emission originating prior to the formation of an HII region around the central
star, or from the central object being too cool to produce a HII region. One
way to distinguish between the two scenarios is to determine and model the
spectral energy distributions (SEDs) of the masers. We observed a sample of 20
6.7 GHz methanol masers selected from the blind Arecibo survey, from centimeter
to submillimeter wavelengths. We combined our observations with existing data
from various Galactic plane surveys to determine SEDs from centimeter to
near-infrared wavelengths. We find that 70% of the masers do not have any
associated radio continuum, with the rest of the sources being associated with
hypercompact and ultracompact HII regions. Modeling the SEDs shows them to be
consistent with rapidly accreting massive stars, with accretion rates well
above 10^{-3} M_sun/yr. The upper limits on the radio continuum are also
consistent with any ionized region being confined close to the stellar surface.
This confirms the paradigm of 6.7 GHz methanol masers being signposts of early
phases of massive star formation, mostly prior to the formation of a
hypercompact HII region.Comment: 15 pages, 4 figures; Accepted by A&
Postprandial morphological response of the intestinal epithelium of the Burmese python (Python molurus)
The postprandial morphological changes of the intestinal epithelium of
Burmese pythons were examined using fasting pythons and at eight time points
after feeding. In fasting pythons, tightly packed enterocytes possess very
short microvilli and are arranged in a pseudostratified fashion. Enterocyte
width increases by 23% within 24 h postfeeding, inducing significant increases
in villus length and intestinal mass. By 6 days postfeeding, enterocyte volume
had peaked, following as much as an 80% increase. Contributing to enterocyte
hypertrophy is the cellular accumulation of lipid droplets at the tips and
edges of the villi of the proximal and middle small intestine, but which were
absent in the distal small intestine. At 3 days postfeeding, conventional and
environmental scanning electron microscopy revealed cracks and lipid extrusion
along the narrow edges of the villi and at the villus tips. Transmission
electron microscopy demonstrated the rapid postprandial lengthening of
enterocyte microvilli, increasing 4.8-fold in length within 24 h, and the
maintaining of that length through digestion. Beginning at 24 h postfeeding,
spherical particles were found embedded apically within enterocytes of the
proximal and middle small intestine. These particles possessed an annular-like
construction and were stained with the calcium-stain Alizarine red S suggesting
that they were bone in origin. Following the completion of digestion, many of
the postprandial responses were reversed, as observed by the atrophy of
enterocytes, the shortening of villi, and the retraction of the microvilli.
Further exploration of the python intestine will reveal the underlying
mechanisms of these trophic responses and the origin and fate of the engulfed
particles
High mass star formation in the IRAS 17233-3606 region: a new nearby and bright hot core in the southern sky
We present molecular line observations of the massive star forming region
IRAS 17233-3606 aimed at studying the molecular core associated with the
source. The observations were made using the Atacama Pathfinder Experiment
telescope in the CO (3-2) and HCO^+ (4-3) transitions, and in the CH_3OH
(6_K-5_K), (7_K-6_K) and CH_3CN (16_K-15_K) bands. For the CO(3-2) and HCO^+
(4-3) transitions, we obtained maps with a size of 70''\times 70''. The typical
angular resolution of the data is ~18''. Our observations reveal an
exceptionally rich molecular spectrum, a signpost of hot core activity.
Comparisons with two other prominent southern hot cores were made through
observations in the same frequency setups. We also detected a bipolar outflow
in CO (3-2) and HCO^+ (4-3) lines. Modelling reveals a hot core of size ~3''
and a temperature of 150 K in the IRAS17233-3606 region. The parameters of the
molecular outflow are derived through the analysis of the CO (3-2) emission,
and are typical of outflows driven by high-mass young stellar objects.Comment: 9 pages, 10 figures (plus 8 figures as Online material), accepted by
A&
High-mass star formation at high luminosities: W31 at >10^6 L_sun
Context: High-mass star formation has been a very active field over the last
decade, however, most studies targeted regions of luminosities between 10^4 and
10^5 L_sun. Methods: We selected the W31 star-forming complex with a total
luminosity of ~6x10^6 L_sun for a multi-wavelength spectral line and continuum
study covering wavelengths from the near- and mid-infrared via (sub)mm
wavelength observations to radio data in the cm regime. Results: While the
overall structure of the multi-wavelength continuum data resembles each other
well, there are several intriguing differences. The 24mum emission stemming
largely from small dust grains follows tightly the spatial structure of the cm
emission tracing the ionized free-free emission. Hence warm dust resides in
regions that are spatially associated with the ionized hot gas (~10^4 K) of the
HII regions. Furthermore, we find several evolutionary stages within the same
complexes, ranging from infrared-observable clusters, via deeply embedded
regions associated with active star formation traced by 24\,m and cm
emission, to at least one high-mass gas clump devoid of any such signature. The
13CO(2-1) and C18O(2-1) spectral line observations reveal a large kinematic
breadth in the entire region with a total velocity range of approximately 90
km/s. While the average virial mass ratio for W31 is close to unity, the line
width analysis indicates large-scale evolutionary differences between the
southern and northern sub-regions (G10.2-0.3 and G10.3-0.1) of the whole W31
complex. The clump mass function - tracing cluster scales and not scales of
individual stars - derived from the 875mum continuum data has a slope of
1.5+-0.3, consistent with previous cloud mass functions.Comment: 13 pages, 11 figures, accepted for Astronomy and Astrophysics,
high-resolution version of paper at
http://www.mpia.de/homes/beuther/papers.htm
A scoping study of IPM compatible options for the management of key vegetable sucking pests: Final report (Project Number: VG06094)
BACKGROUND BRIEFING The availability of specific soft option products for other pests such as Lepidoptera species control in vegetables has increased the importance of sucking pests in the modern day pest spectrum. Current vegetable sucking pest management practices are still heavily reliant on older broad spectrum pesticides. These non selective products prevent further adoption of an integrated pest management (IPM) system, and their frequent, multiple crop use pattern has the potential to enhance resistance development in the pest population. A limited number of more recently developed, pest specific or “softer” products for example spinosad (Success®) and pymetrozine (Chess®) are registered in some specific vegetable crops. The management of sucking pests is also complicated by the fact that virus transmission and product contamination are as, if not more important than the physical damage they can cause to vegetable crops. To modernise sucking pest control in the vegetable sector, work in a range of overlapping multifaceted areas needs to occur. A team of entomologist in consultation with crop consultants, growers and specialist reviewers conducted a scoping study of the impact of at least 5 sucking pests commonly found across vegetable crops. Literature reviews, an industry workshop, interstate producer interviews and farm visits were employed to collate information on current best 'fit' management options within an IPM system, relevant to the particular vegetable and potential future management options. Ideas for future research, development, and extension activities highlighted in the workshop process included ; biopesticides, improved beneficial insect management in current cropping systems, monitoring and early warning, improved knowledge of pest ecology, resistance issues, improved soft option products, increased grower awareness and information, extension and publications. Developing and testing fungal biopesticides against sucking pests, managing insecticide resistance and field testing biocontrol agents against thrips were considered the top three topics for further research of 28 topics listed and prioritised by the workshop participants
A study of three southern high-mass star-forming regions
Based on color-selected IRAS point sources, we have started to conduct a
survey of 47 high-mass star-forming regions in the southern hemisphere in 870um
dust continuum and molecular line emission in several frequency ranges between
290 GHz and 806 GHz. This paper describes the pilot study of the three sources
IRAS12326-6245, IRAS16060-5146, and IRAS16065-5158. To characterize the
physical and chemical properties of southern massive star-forming regions, the
three high-luminosity southern hemisphere hot cores were observed with APEX in
five frequency setups aimed at groups of lines from the following molecules:
CH3OH, H2CO, and CH3CN. Using the LTE approximation, temperatures, source
sizes, and column densities were determined through modeling of synthetic
spectra with the XCLASS program. Dust continuum observations were done with the
Large APEX BOlometer CAmera (LABOCA) at 870um and the 3mm continuum was imaged
with the ATCA. Based on the detection of high-excitation CH3CN lines and lines
from complex organic species, the three sources are classified as line rich,
hot core type sources. For all three, the modeling indicates that the line
emission emerges from a combination of an extended, cooler envelope, and a hot
compact component. All three sources show an overabundance of oxygen-bearing
species compared to nitrogen-bearing species. Based on the results obtained in
the three sources, which served as templates for the survey, the most promising
(and feasible) frequency setups for the remaining 44 sources were decided upon.Comment: 18 pages, 28 figures plus 23 pages online material; accepted for
publication in A&
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