8,845 research outputs found
Globular Clusters in the Sombrero Galaxy (NGC 4594)
The Sombrero galaxy, NGC 4594, contains the most numerous globular cluster
system of any nearby spiral. It is an ideal candidate in which to study the
globular clusters and contrast them with those in Local Group spirals. Here we
present B and I imaging from the CTIO Schmidt telescope which gives a
field-of-view of 31' x 31'. Using DAOPHOT we have detected over 400 globular
clusters and derived their magnitudes, B--I colors and photometric
metallicities. We have attempted to separate our sample into disk and
bulge/halo globular cluster populations, based on location in the galaxy. There
is some evidence that the disk population is more metal--rich than the
bulge/halo globular clusters, however contamination, dust reddening and small
number statistics makes this result very tentative. We find that the median
metallicity of the bulge/halo globular clusters is [Fe/H] = -0.8. This
metallicity is consistent with previous estimates based on smaller samples. It
is also similar to the metallicity predicted by the globular cluster
metallicity -- galaxy luminosity relation. As with our Galaxy, there is no
radial metallicity gradient in the halo globular clusters. This suggests that
the spheriodal component of NGC 4594 did not form by a dissipational process.Comment: 7 pages, Latex. To be published in the Astronomical Journal. Full
paper available at http://www.ucolick.org/~forbes/home.htm
The Purple Haze of Eta Carinae: Binary-Induced Variability?
Asymmetric variability in ultraviolet images of the Homunculus obtained with
the Advanced Camera for Surveys/High Resolution Camera on the Hubble Space
Telescope suggests that Eta Carinae is indeed a binary system. Images obtained
before, during, and after the recent ``spectroscopic event'' in 2003.5 show
alternating patterns of bright spots and shadows on opposite sides of the star
before and after the event, providing a strong geometric argument for an
azimuthally-evolving, asymmetric UV radiation field as one might predict in
some binary models. The simplest interpretation of these UV images, where
excess UV escapes from the secondary star in the direction away from the
primary, places the major axis of the eccentric orbit roughly perpendicular to
our line of sight, sharing the same equatorial plane as the Homunculus, and
with apastron for the hot secondary star oriented toward the southwest of the
primary. However, other orbital orientations may be allowed with more
complicated geometries. Selective UV illumination of the wind and ejecta may be
partly responsible for line profile variations seen in spectra. The brightness
asymmetries cannot be explained plausibly with delays due to light travel time
alone, so a single-star model would require a seriously asymmetric shell
ejection.Comment: 8 pages, fig 1 in color, accepted by ApJ Letter
Characterization of dengue virus entry into HepG2 cells
<p>Abstract</p> <p>Background</p> <p>Despite infections by the dengue virus being a significant problem in tropical and sub-tropical countries, the mechanism by which the dengue virus enters into mammalian cells remains poorly described.</p> <p>Methods</p> <p>A combination of biochemical inhibition, dominant negative transfection of Eps15 and siRNA mediated gene silencing was used to explore the entry mechanism of dengue into HepG2 cells.</p> <p>Results</p> <p>Results were consistent with entry via multiple pathways, specifically via clathrin coated pit mediated endocytosis and macropinocytosis, with clathrin mediated endocytosis being the predominant pathway.</p> <p>Conclusion</p> <p>We propose that entry of the dengue virus to mammalian cells can occur by multiple pathways, and this opens the possibility of the virus being directed to multiple cellular compartments. This would have significant implications in understanding the interaction of the dengue virus with the host cell machinery.</p
A rapid, chromatography-free route to substituted acridine–isoalloxazine conjugates under microwave irradiation
Microwave irradiation was applied to a sequence of condensation reactions from readily available 9-chloroacridines to provide a range of novel acridine–isoalloxazine conjugates. The combination of these two moieties, both of biological interest, was achieved by a chromatography free route
One-pot access to L-5,6-dihalotryptophans and L-alknyltryptophans using tryptophan synthase
The authors thank the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007-2013/ERC grant agreement no 614779, and the University of St Andrews for a studentship (to D. R. M. Smith).We report, for the first time, the use of tryptophan synthase in the generation of L- dihalotryptophans and L-alkynyltryptophans. These previously unpublished compounds will be useful tools in the generation of probes for chemical biology, in biosynthetic diversification and as convenient building blocks for synthesis.PostprintPeer reviewe
LiBeB: High and low energy cosmic ray production and comparison with neutrino induced nucleosynthesis in SNII
We present new calculations of LiBeB production by accelerated particles with
various compositions and energy spectra ranging from low energies to
relativistic energies, and various ambient medium metallicities ().
The observed, essentially constant, Be/Fe ratio as a function of
can be best understood if the metallicity of the accelerated particles (high
energy or low energy) does not vary much with . This could be
achieved if the particles are accelerated directly from the ejecta of Type II
supernovae (SNII) and not from the interstellar medium. Using the observed
Be/Fe and the fact that most of the Fe at low is from SNII, we
derive the energy content in accelerated particles per SNII (a few times
10 erg). We show that additional B production by neutrinos is
consistent with the available data, allowing a neutrino yield from SNII less
than or equal to the nominal published yields. We further show that the
observed Li at low suggests that the accelerated particles
responsible for the LiBeB at such are confined to low energies and
have a relatively high He/O abundance.Comment: 9 pages with 4 emdedded figures, uuencoded, compressed, tared, style
files included. In press Nuclei In the Cosmos, Nuclear Physics, Conference
Proceeding
Two Large HI Shells in the Outer Galaxy near l=279 degrees
As part of a survey of HI 21-cm emission in the Southern Milky Way, we have
detected two large shells in the interstellar neutral hydrogen near l=279 deg.
The center velocities are +36 and +59 km/s, which puts the shells at kinematic
distances of 7 and 10 kpc. The larger shell is about 610 pc in diameter and
very empty, with density contrast of at least 15 between the middle and the
shell walls. It has expansion velocity of about 20 km/s and swept up mass of
several million solar masses. The energy indicated by the expansion may be as
high as 2.4 X 10^53 ergs. We estimate its age to be 15 to 20 million years. The
smaller shell has diameter of about 400 pc, expansion velocity about 10 km/s
and swept up mass of about 10^6 solar masses.
Morphologically both regions appear to be shells, with high density regions
mostly surrounding the voids, although the first appears to have channels of
low density which connect with the halo above and below the HI layer. They lie
on the edge of the Carina arm, which suggests that they may be expanding
horizontally into the interarm region as well as vertically out of the disk. If
this interpretation is correct, this is the first detection of an HI chimney
which has blown out of both sides of the disk.Comment: 21 pages, 14 jpeg figures, accepted for publication in A
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