3,397 research outputs found
New control for Esperance armyworms
Armyworms are periodically responsible for serious cereal crop damage in Australia, often causing up to 80 per cent crop loss.
Amajor outbreak at Esperance in 1975 resulted in some 14,200 ha requiring treatment.
This was the first serious outbreak of armyworm for nine years in Western Australia.
A major new problem in the control of armyworm outbreaks is that use of DDT has been restricted by residue and withholding period problems, especially with a crop such as barley in which the grain is unprotected by glumes.
The trial results suggest that trichlorfon is a suitable material to eradicate armyworms and that timing of the applications will be of paramount importance
FUSE Observations of Outflowing OVI in the Dwarf Starburst Galaxy NGC1705
We report FUSE far-UV spectroscopy of the prototypical dwarf starburst galaxy
NGC 1705. These data allow us for the first time to probe the coronal-phase gas
(T = 10E5 to 10E6 K) that may dominate the radiative cooling of the
supernova-heated ISM and thereby determine the dynamical evolution of
starburst-driven outflows. We detect a broad (100 km/s) and blueshifted (by 80
km/s) OVI absorption-line arising in the previously-known galactic outflow. The
properties of the OVI absorption are inconsistent with the standard superbubble
model in which this gas arises in a conductive interface inside the outer
shell. We show that the superbubble in NGC 1705 is blowing out of the galaxy
ISM. During blow-out, coronal-phase gas can be created by hydrodynamical mixing
as hot gas rushes out through fissures in the fragmenting shell of cool gas. As
the coronal gas cools radiatively, it can naturally produce the observed OVI
column density and outflow speed. The OVI data show that the cooling rate in
the coronal-phase gas is less than about 10% of the supernova heating rate.
Since the X-ray luminosity from hotter gas is even smaller, we conclude that
radiative losses are insignificant. The outflow should be able to vent its
metals and kinetic energy out of the galaxy. This process has potentially
important implications for the evolution of dwarf galaxies and the IGM.Comment: ApJ (in press
Chemical Abundances Of Open Clusters From High-Resolution Infrared Spectra. I. NGC 6940
We present near-infrared spectroscopic analysis of 12 red giant members of
the Galactic open cluster NGC 6940. High-resolution (R45000) and high
signal-to-noise ratio (S/N > 100) near-infrared H and K band spectra were
gathered with the Immersion Grating Infrared Spectrograph (IGRINS) on the 2.7m
Smith Telescope at McDonald Observatory. We obtained abundances of H-burning
(C, N, O), (Mg, Si, S, Ca), light odd-Z (Na, Al, P, K), Fe-group
(Sc, Ti, Cr, Fe, Co, Ni) and neutron-capture (Ce, Nd, Yb) elements. We report
the abundances of S, P, K, Ce, and Yb in NGC 6940 for the first time. Many OH
and CN features in the H band were used to obtain O and N abundances. C
abundances were measured from four different features: CO molecular lines in
the K band, high excitation C I lines present in both near-infrared and
optical, CH and bands in the optical region. We have also determined
ratios from the R-branch band heads of first overtone (2-0) and
(3-1) (2-0) lines near 23440
\overset{\lower.5em\circ}{\mathrm{A}} and (3-1) lines at about
23730 \overset{\lower.5em\circ}{\mathrm{A}}. We have also investigated the HF
feature at 23358.3 \overset{\lower.5em\circ}{\mathrm{A}}, finding solar
fluorine abundances without ruling out a slight enhancement. For some elements
(such as the group), IGRINS data yield more internally
self-consistent abundances. We also revisited the CMD of NGC 6940 by
determining the most probable cluster members using Gaia DR2. Finally, we
applied Victoria isochrones and MESA models in order to refine our estimates of
the evolutionary stages of our targets.Comment: 16 pages, 10 figure
Mapping Lyme Disease Incidence for Diagnostic and Preventive Decisions, Maryland
To support diagnostic and preventive decision making, we analyzed incidence of Lyme disease in Maryland on the zip code level. Areas of high incidence were identified on the Upper Eastern Shore of the Chesapeake Bay and in counties north and east of Baltimore City. These latter foci, especially, are not visible when mapping Lyme disease on the county level.
The dynamics and high-energy emission of conductive gas clouds in supernova-driven galactic superwinds
In this paper we present high-resolution hydrodynamical models of warm
ionized clouds embedded in a superwind, and compare the OVI and soft X-ray
properties to the existing observational data. These models include thermal
conduction, which we show plays an important role in shaping both the dynamics
and radiative properties of the resulting wind/cloud interaction. Heat
conduction stabilizes the cloud by inhibiting the growth of K-H and R-T
instabilities, and also generates a shock wave at the cloud's surface that
compresses the cloud. This dynamical behaviour influences the observable
properties. We find that while OVI emission and absorption always arises in
cloud material at the periphery of the cloud, most of the soft X-ray arises in
the region between the wind bow shock and the cloud surface, and probes either
wind or cloud material depending on the strength of conduction and the relative
abundances of the wind with respect to the cloud. In general only a small
fraction (<1%) of the wind mechanical energy intersecting a cloud is radiated
away at UV and X-ray wavelengths, with more wind energy going into accelerating
the cloud. Models with heat conduction at Spitzer-levels are found to produce
observational properties closer to those observed in superwinds than models
with no thermal conduction, in particular in terms of the OVI-to-X-ray
luminosity ratio, but cloud life times are uncomfortably short (<1Myr) compared
to the dynamical ages of real winds. We experimented with reducing the thermal
conductivity and found that even when we reduced conduction by a factor of 25
that the simulations retained the beneficial hydrodynamical stability and low
O{\sc vi}-to-X-ray luminosity ratio found in the Spitzer-level conductive
models, while also having reduced evaporation rates.Comment: 27 pages, 12 figures (4 in color), MNRAS accepte
Properties of Galactic Outflows: Measurements of the Feedback from Star Formation
Properties of starburst-driven outflows in dwarf galaxies are compared to
those in more massive galaxies. Over a factor of roughly 10 in galactic
rotation speed, supershells are shown to lift warm ionized gas out of the disk
at rates up to several times the star formation rate. The amount of mass
escaping the galactic potential, in contrast to the disk, does depend on the
galactic mass. The temperature of the hottest extended \x emission shows little
variation around K, and this gas has enough energy to escape
from the galaxies with rotation speed less than approximately 130 km/s.Comment: 11 pages + 3 figues. Accepted for publication in the Astrophysical
Journa
Observational Constraints on Superbubble X-ray Energy Budgets
The hot, X-ray-emitting gas in superbubbles imparts energy and enriched
material to the interstellar medium (ISM) and generates the hot ionized medium,
the ISM's high-temperature component. The evolution of superbubble energy
budgets is not well understood, however, and the processes responsible for
enhanced X-ray emission in superbubbles remain a matter of debate. We present
Chandra ACIS-S observations of two X-ray-bright superbubbles in the Large
Magellanic Cloud (LMC), DEM L50 (N186) and DEM L152 (N44), with an emphasis on
disentangling the true superbubble X-ray emission from non-related diffuse
emission and determining the spatial origin and spectral variation of the X-ray
emission. An examination of the superbubble energy budgets shows that on the
order of 50% of the X-ray emission comes from regions associated with supernova
remnant (SNR) impacts. We find some evidence of mass-loading due to swept-up
clouds and metallicity enrichment, but neither mechanism provides a significant
contribution to the X-ray luminosities. We also find that one of the
superbubbles, DEM L50, is likely not in collisional ionization equilibrium. We
compare our observations to the predictions of the standard Weaver et al. model
and to 1-D hydrodynamic simulations including cavity supernova impacts on the
shell walls. Our observations show that mass-loading due to thermal evaporation
from the shell walls and SNR impacts are the dominant source of enhanced X-ray
luminosities in superbubbles. These two processes should affect most
superbubbles, and their contribution to the X-ray luminosity must be considered
when determining the energy available for transport to the ISM.Comment: 25 pages, 11 figures, accepted for publication in Ap
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