1,016 research outputs found
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Petrography and bulk composition of Miller Range 05035: a new lunar VLT gabbro
Miller Range (MIL) 05035 is a crystalline lunar mare gabbroic meteorite collected in Antarctica in 2005 [1]. It is an important new sample in the lunar meteorite (LM) collection as it is only one of ~8 to be classified as basaltic in nature. MIL 05035 is coarsely grained with large pyroxene grains ( 8mm) subophitically enclosing plagioclase grains ( 6mm), and accessory ilmenite, spinel, silica and sulphide phases
The X-ray luminous cluster underlying the z = 1.04 quasar PKS1229-021
We present a 100 ks Chandra observation studying the extended X-ray emission
around the powerful z=1.04 quasar PKS1229-021. The diffuse cluster X-ray
emission can be traced out to ~15 arcsec (~120 kpc) radius and there is a drop
in the calculated hardness ratio inside the central 5 arcsec consistent with
the presence of a cool core. Radio observations of the quasar show a strong
core and a bright, one-sided jet leading to the SW hot spot and a second hot
spot visible on the counter-jet side. Although the wings of the quasar PSF
provided a significant contribution to the total X-ray flux at all radii where
the extended cluster emission was detected, we were able to accurately subtract
off the PSF emission using ChaRT and marx simulations. The resulting steep
cluster surface brightness profile for PKS1229-021 appears similar to the
profile for the FRII radio galaxy 3C444, which has a similarly rapid surface
brightness drop caused by a powerful shock surrounding the radio lobes (Croston
et al.). Using a model surface brightness profile based on 3C444, we estimated
the total cluster luminosity for PKS1229-021 to be L_X ~ 2 x 10^{44} erg/s. We
discuss the difficulty of detecting cool core clusters, which host bright X-ray
sources, in high redshift surveys.Comment: 10 pages, 9 figures, accepted by MNRA
Evolution from protoplanetary to debris discs: The transition disc around HD 166191
HD 166191 has been identified by several studies as hosting a rare and
extremely bright warm debris disc with an additional outer cool disc component.
However, an alternative interpretation is that the star hosts a disc that is
currently in transition between a full gas disc and a largely gas-free debris
disc. With the help of new optical to mid-IR spectra and Herschel imaging, we
argue that the latter interpretation is supported in several ways: i) we show
that HD 166191 is co-moving with the ~4 Myr-old Herbig Ae star HD 163296,
suggesting that the two have the same age, ii) the disc spectrum of HD 166191
is well matched by a standard radiative transfer model of a gaseous
protoplanetary disc with an inner hole, and iii) the HD 166191 mid-IR silicate
feature is more consistent with similarly primordial objects. We note some
potential issues with the debris disc interpretation that should be considered
for such extreme objects, whose lifetime at the current brightness is mush
shorter than the stellar age, or in the case of the outer component requires a
mass comparable to the solid component of the Solar nebula. These aspects
individually and collectively argue that HD 166191 is a 4-5 Myr old star that
hosts a gaseous transition disc. Though it does not argue in favour of either
scenario, we find strong evidence for 3-5 um disc variability. We place HD
166191 in context with discs at different evolutionary stages, showing that it
is a potentially important object for understanding the protoplanetary to
debris disc transition.Comment: accepted to MNRAS, fixed typos in abstract and axis labe
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Gut inflammation provides a respiratory electron acceptor for Salmonella.
Salmonella enterica serotype Typhimurium (S. Typhimurium) causes acute gut inflammation by using its virulence factors to invade the intestinal epithelium and survive in mucosal macrophages. The inflammatory response enhances the transmission success of S. Typhimurium by promoting its outgrowth in the gut lumen through unknown mechanisms. Here we show that reactive oxygen species generated during inflammation react with endogenous, luminal sulphur compounds (thiosulphate) to form a new respiratory electron acceptor, tetrathionate. The genes conferring the ability to use tetrathionate as an electron acceptor produce a growth advantage for S. Typhimurium over the competing microbiota in the lumen of the inflamed gut. We conclude that S. Typhimurium virulence factors induce host-driven production of a new electron acceptor that allows the pathogen to use respiration to compete with fermenting gut microbes. Thus the ability to trigger intestinal inflammation is crucial for the biology of this diarrhoeal pathogen
Computer Components and Systems
Contains reports on three research projects.United States Navy, Bureau of Ships (Contract NObsr 77603
XMMU J0541.8-6659, a new supernova remnant in the Large Magellanic Cloud
The high sensitivity of the XMM-Newton instrumentation offers the opportunity
to study faint and extended sources in the Milky Way and nearby galaxies such
as the Large Magellanic Cloud (LMC) in detail. The ROSAT PSPC survey of the LMC
has revealed more than 700 X-ray sources, among which there are 46 supernova
remnants (SNRs) and candidates. We have observed the field around one of the
most promising SNR candidates in the ROSAT PSPC catalogue, labelled [HP99] 456
with XMM-Newton, to determine its nature. We investigated the XMM-Newton data
along with new radio-continuum, near infrared and optical data. In particular,
spectral and morphological studies of the X-ray and radio data were performed.
The X-ray images obtained in different energy bands reveal two different
structures. Below 1.0 keV the X-ray emission shows the shell-like morphology of
an SNR with a diameter of ~73 pc, one of the largest known in the LMC. For its
thermal spectrum we estimate an electron temperature of (0.49 +/- 0.12)keV
assuming non-equilibrium ionisation. The X-ray images above 1.0 keV reveal a
less extended source within the SNR emission, located ~1' west of the centre of
the SNR and coincident with bright point sources detected in radio-continuum.
This hard component has an extent of 0.9' (i.e. ~13 pc at a distance of ~50
kpc) and a non-thermal spectrum. The hard source coincides in position with the
ROSAT source [HP99] 456 and shows an indication for substructure. We firmly
identify a new SNR in the LMC with a shell-like morphology and a thermal
spectrum. Assuming the SNR to be in the Sedov phase yields an age of ~23 kyr.
We explore possible associations of the hard non-thermal emitting component
with a pulsar wind nebula (PWN) or background active galactic nuclei (AGN).Comment: 8 pages, 7 figures, accepted for publication in Astronomy and
Astrophysic
The X-ray luminous cluster underlying the bright radio-quiet quasar H1821+643
We present a Chandra observation of the only low redshift, z=0.299, galaxy
cluster to contain a highly luminous radio-quiet quasar, H1821+643. By
simulating the quasar PSF, we subtract the quasar contribution from the cluster
core and determine the physical properties of the cluster gas down to 3 arcsec
(15 kpc) from the point source. The temperature of the cluster gas decreases
from 9.0\pm0.5 keV down to 1.3\pm0.2 keV in the centre, with a short central
radiative cooling time of 1.0\pm0.1 Gyr, typical of a strong cool-core cluster.
The X-ray morphology in the central 100 kpc shows extended spurs of emission
from the core, a small radio cavity and a weak shock or cold front forming a
semi-circular edge at 15 arcsec radius. The quasar bolometric luminosity was
estimated to be 2 x 10^{47} erg per sec, requiring a mass accretion rate of 40
Msolar per yr, which corresponds to half the Eddington accretion rate. We
explore possible accretion mechanisms for this object and determine that Bondi
accretion, when boosted by Compton cooling of the accretion material, could
provide a significant source of the fuel for this outburst. We consider
H1821+643 in the context of a unified AGN accretion model and, by comparing
H1821+643 with a sample of galaxy clusters, we show that the quasar has not
significantly affected the large-scale cluster gas properties.Comment: 20 pages, 19 figures, accepted by MNRA
Multi-frequency study of DEM L299 in the Large Magellanic Cloud
We have studied the HII region DEM L299 in the Large Magellanic Cloud to
understand its physical characteristics and morphology in different
wavelengths. We performed a spectral analysis of archived XMM-Newton EPIC data
and studied the morphology of DEM L299 in X-ray, optical, and radio
wavelengths. We used H alpha, [SII], and [OIII] data from the Magellanic Cloud
Emission Line Survey and radio 21 cm line data from the Australia Telescope
Compact Array (ATCA) and the Parkes telescope, and radio continuum data from
ATCA and the Molonglo Synthesis Telescope. Our morphological studies imply
that, in addition to the supernova remnant SNR B0543-68.9 reported in previous
studies, a superbubble also overlaps the SNR in projection. The position of the
SNR is clearly defined through the [SII]/H alpha flux ratio image. Moreover,
the optical images show a shell-like structure that is located farther to the
north and is filled with diffuse X-ray emission, which again indicates the
superbubble. Radio 21 cm line data show a shell around both objects. Radio
continuum data show diffuse emission at the position of DEM L299, which appears
clearly distinguished from the HII region N 164 that lies south-west of it. We
determined the spectral index of SNR B0543-68.9 to be alpha=-0.34, which
indicates the dominance of thermal emission and therefore a rather mature SNR.
We determined the basic properties of the diffuse X-ray emission for the SNR,
the superbubble, and a possible blowout region of the bubble, as suggested by
the optical and X-ray data. We obtained an age of 8.9 (3.5-18.1) kyr for the
SNR and a temperature of 0.64 (0.44-1.37) keV for the hot gas inside the SNR,
and a temperature of the hot gas inside the superbubble of 0.74 (0.44-1.1) keV.
We conclude that DEM L299 consists of a superposition of SNR B0543-68.9 and a
superbubble, which we identified based on optical data.Comment: Accepted for publication in Astronomy and Astrophysics. 17 pages, 16
figure
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Observations of Past Lunar Landing Sites by the D-CIXS X-Ray Spectrometer on SMART-1
D-CIXS initial observations show a first unambiguous remote sensing of calcium in the lunar regolith. Data obtained are broadly consistent with current understanding of mare and highland composition. Ground truth is provided by the returned Apollo and Luna sample sets
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