982 research outputs found
Evidence for a Young Stellar Population in NGC 5018
Two absorption line indices, Ca II and Hdelta/FeI4045, measured from high
resolution spectra are used with evolutionary synthesis models to verify the
presence of a young stellar population in NGC 5018. The derived age of this
population is about ~2.8 Gyr with a metallicity roughly solar and it completely
dominates the integrated light of the galaxy near 4000 A.Comment: 13 pages, 7 figures (figs 3-7 are color figures), to be published in
the May 2000 issue of the Astrophysical Journa
Spherical harmonic representation of the main geomagnetic field for world charting and investigations of some fundamental problems of physics and geophysics
The data processing of MAGSAT investigator B test tapes and data tapes, and tapes of selected data on 15 magnetically quiet days is reported. The 1980 World Chart spherical model was compared with the MAGSAT (3/80) and MAGSAT vector data were used in the models. An article on modelling the geomagnetic field using satellite data is included
Spherical harmonic representation of the main geomagnetic field for world charting and investigations of some fundamental problems of physics and geophysics
Quiet-day data from MAGSAT were examined for effects which might test the validity of Maxwell's equations. Both external and toroidal fields which might represent a violation of the equations appear to exist, well within the associated errors. The external field might be associated with the ring current, and varies of a time-scale of one day or less. Its orientation is parallel to the geomagnetic dipole. The toriodal field can be confused with an orientation in error (in yaw). It the toroidal field really exists, its can be related to either ionospheric currents, or to toroidal fields in the Earth's core in accordance with Einstein's unified field theory, or to both
Timing of surgery following SARS-CoV-2 infection : an international prospective cohort study
Peri-operative SARS-CoV-2 infection increases postoperative mortality. The aim of this study was to determine the optimal duration of planned delay before surgery in patients who have had SARS-CoV-2 infection. This international, multicentre, prospective cohort study included patients undergoing elective or emergency surgery during October 2020. Surgical patients with pre-operative SARS-CoV-2 infection were compared with those without previous SARS-CoV-2 infection. The primary outcome measure was 30-day postoperative mortality. Logistic regression models were used to calculate adjusted 30-day mortality rates stratified by time from diagnosis of SARS-CoV-2 infection to surgery. Among 140,231 patients (116 countries), 3127 patients (2.2%) had a pre-operative SARS-CoV-2 diagnosis. Adjusted 30-day mortality in patients without SARS-CoV-2 infection was 1.5% (95%CI 1.4-1.5). In patients with a pre-operative SARS-CoV-2 diagnosis, mortality was increased in patients having surgery within 0-2 weeks, 3-4 weeks and 5-6 weeks of the diagnosis (odds ratio (95%CI) 4.1% (3.3-4.8), 3.9% (2.6-5.1) and 3.6% (2.0-5.2), respectively). Surgery performed >= 7 weeks after SARS-CoV-2 diagnosis was associated with a similar mortality risk to baseline (odds ratio (95%CI) 1.5% (0.9-2.1%)). After a >= 7 week delay in undertaking surgery following SARS-CoV-2 infection, patients with ongoing symptoms had a higher mortality than patients whose symptoms had resolved or who had been asymptomatic (6.0% (95%CI 3.2-8.7) vs. 2.4% (95%CI 1.4-3.4) vs. 1.3% (95%CI 0.6-2.0%), respectively). Where possible, surgery should be delayed for at least 7 weeks following SARS-CoV-2 infection. Patients with ongoing symptoms >= 7 weeks from diagnosis may benefit from further delay.Peer reviewe
Limits on eclipses of the pre-main-sequence star KH 15D in the first half of the 20th century
Over the last decade, the pre-main sequence star KH 15D has exhibited
periodic eclipses that are surprisingly deep (~3 mag) and long-lasting (~40% of
the 48.4-day period). The cause of the eclipses is unknown, but it could be a
feature in a nearly edge-on protoplanetary disk. Here we report on an analysis
of archival photographs of KH 15D from the Harvard College Observatory plate
collection, most of which were taken during the years 1913-1951. During this
time range, the data are consistent with no eclipses; the duty cycle of 1 mag
eclipses was less than 20%. The decadal timescale of this change in eclipse
behavior is compatible with the expected timescale of protoplanet/disk
interactions. Archival images from more recent epochs should reveal the onset
of the eclipses.Comment: ApJ Letters, in press [10pp, 4 figs
Molecular Gas, Dust and Star Formation in the Barred Spiral NGC 5383
We present multi-wavelength (interferometer and single-dish CO J=1-0, Halpha,
broadband optical and near-infrared) observations of the classic barred spiral
NGC 5383. We compare the observed central gas and dust morphology to the
predictions of recent hydrodynamic simulations. In the nuclear region, our
observations reveal three peaks lying along a S-shaped gas and dust
distribution. In contrast, the model predicts a circumnuclear ring, not the
observed S-shaped distribution; moreover, the predicted surface density
contrast between the central gas accumulation and the bar dust lanes is an
order of magnitude larger than observed. The discrepancies are not due to
unexplored model parameter space or a nuclear bar but are probably due to the
vigorous (7 solar masses per year) star formation activity in the center.
As is common in similar bars, the star formation rate in the bar between the
bar ends and the central region is low (~0.5 solar masses per yr), despite the
high gas column density in the bar dust lanes; this is generally attributed to
shear and shocks. We note a tendency for the HII regions to be associated with
the spurs feeding the main bar dust lanes, but these are located on the leading
side of the bar. We propose that stars form in the spurs, which provide a high
column density but low shear environment. HII regions can therefore be found
even on the leading side of the bar because the ionizing stars pass
ballistically through the dust laneComment: Accepted for publication in The Astrophysical Journal, 33 pages
(includes 10 figures
HIPASS Detection of an Intergalactic Gas Cloud in the NGC 2442 Group
We report the discovery, from the HI Parkes All-Sky Survey (HIPASS), of a gas
cloud associated with the asymmetric spiral galaxy NGC 2442. This object,
designated HIPASS J0731-69, contains ~10^9 M_sun of HI, or nearly one-third as
much atomic gas as NGC 2442 itself. No optical counterpart to any part of
HIPASS J0731-69 has yet been identified, consistent with the gas being diffuse,
and with its stream-like kinematics. If the gas in HIPASS J0731-69 was once
part of NGC 2442, then it was most likely a fairly recent tidal encounter with
a moderately massive companion which tore it loose, although the possibility of
ram-pressure stripping cannot be ruled out. This discovery highlights the
potential of the HIPASS data for yielding new clues to the nature of some of
the best-known galaxies in the local universe.Comment: 8 pages, 4 figures, uses "emulateapj5.sty". Accepted for publication
in ApJ, Vol. 555, 1 July 2001. Figs 1 and 2 included as JPE
The disruption of nearby galaxies by the Milky Way
Interactions between galaxies are common and are an important factor in
determining their physical properties such as position along the Hubble
sequence and star-formation rate. There are many possible galaxy interaction
mechanisms, including merging, ram-pressure stripping, gas compression,
gravitational interaction and cluster tides. The relative importance of these
mechanisms is often not clear, as their strength depends on poorly known
parameters such as the density, extent and nature of the massive dark halos
that surround galaxies. A nearby example of a galaxy interaction where the
mechanism is controversial is that between our own Galaxy and two of its
neighbours -- the Large and Small Magellanic Clouds. Here we present the first
results of a new HI survey which provides a spectacular view of this
interaction. In addition to the previously known Magellanic Stream, which
trails 100 degrees behind the Clouds, the new data reveal a counter-stream
which lies in the opposite direction and leads the motion of the Clouds. This
result supports the gravitational model in which leading and trailing streams
are tidally torn from the body of the Magellanic Clouds.Comment: 17 pages with 5 figures in gif format, scheduled for publication in
the August 20th, 1998 issue of Natur
Preservation of the metaproteome: variability of protein preservation in ancient dental calculus.
Proteomic analysis of dental calculus is emerging as a powerful tool for disease and dietary characterisation of archaeological populations. To better understand the variability in protein results from dental calculus, we analysed 21 samples from three Roman-period populations to compare: 1) the quantity of extracted protein; 2) the number of mass spectral queries; and 3) the number of peptide spectral matches and protein identifications. We found little correlation between the quantity of calculus analysed and total protein identifications, as well as no systematic trends between site location and protein preservation. We identified a wide range of individual variability, which may be associated with the mechanisms of calculus formation and/or post-depositional contamination, in addition to taphonomic factors. Our results suggest dental calculus is indeed a stable, long-term reservoir of proteins as previously reported, but further systematic studies are needed to identify mechanisms associated with protein entrapment and survival in dental calculus
More evidence for hidden spiral and bar features in bright early-type dwarf galaxies
Following the discovery of spiral structure in IC3328 (Jerjen et al.~2000),
we present further evidence that a sizable fraction of bright early-type dwarfs
in the Virgo cluster are genuine disk galaxies, or are hosting a disk
component. Among a sample of 23 nucleated dwarf ellipticals and dS0s observed
with the Very Large Telescope in and , we found another four systems
exhibiting non-axisymmetric structures, such as a bar and/or spiral arms,
indicative of a disk (IC0783, IC3349, NGC4431, IC3468). Particularly remarkable
are the two-armed spiral pattern in IC0783 and the bar and trailing arms in
NGC4431. For both galaxies the disk nature has recently been confirmed by a
rotation velocity measurement (Simien & Prugniel 2002). Our photometric search
is based on a Fourier decomposition method and a specific version of unsharp
masking. Some ``early-type'' dwarfs in the Virgo cluster seem to be former
late-type galaxies which were transformed to early-type morphology, e.g. by
``harassment'', during their infall to the cluster, while maintaining part of
their disk structure.Comment: A&A accepte
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