1,074 research outputs found
Investigating the pre-main sequence magnetic chemically peculiar system HD 72106
The origin of the strong magnetic fields observed in chemically peculiar Ap
and Bp stars stars has long been debated. The recent discovery of magnetic
fields in the intermediate mass pre-main sequence Herbig Ae and Be stars links
them to Ap and Bp stars, providing vital clues about Ap and Bp stars and the
origin and evolution of magnetic fields in intermediate and high mass stars. A
detailed study of one young magnetic B star, HD 72106A, is presented. This star
appears to be in a binary system with an apparently normal Herbig Ae star. A
maximum longitudinal magnetic field strength of +391 +/- 65 G is found in HD
72106A, as are strong chemical peculiarities, with photospheric abundances of
some elements ranging up to 100x above solar.Comment: 8 pages, 6 figures. Proceeding of the 2006 conference of the Special
Astrophysical Observatory of the Russian Academy of Science
The Globular Cluster Systems of NGC 1400 and NGC 1407
The two brightest elliptical galaxies in the Eridanus A group, NGC 1400 and
NGC 1407, have been observed in both the Washington T_1 and Kron-Cousins I
filters to obtain photometry of their globular cluster systems (GCSs). This
group of galaxies is of particular interest due to its exceptionally high M/L
value, previously estimated at ~3000h, making this cluster highly
dark-matter-dominated. NGC 1400's radial velocity (549 km/s) is extremely low
compared to that of the central galaxy of Eridanus A (NGC 1407 with =
1766 km/s) and the other members of the system, suggesting that it is a
foreground galaxy projected by chance onto the cluster. Using the shapes of the
globular cluster luminosity functions, however, we derive distances of 17.6 +/-
3.1 Mpc to NGC 1407 and 25.4 +/- 7.0 Mpc to NGC 1400. These results support
earlier conclusions that NGC 1400 is at the distance of Eridanus A and
therefore has a large peculiar velocity. Specific frequencies are also derived
for these galaxies, yielding values of S_N = 4.0 +/- 1.3 for NGC 1407 and S_N =
5.2 +/- 2.0 for NGC 1400. In this and other respects, these two galaxies have
GCSs which are consistent with those observed in other galaxies.Comment: 14 pages (AASTeX), 3 postscript figures, submitted to the
Astronomical Journa
Substructure in the Andromeda Galaxy Globular Cluster System
In the most prominent current scenario of galaxy formation, galaxies form
hierarchically through the merger of smaller systems. Such mergers could leave
behind dynamical signatures which may linger long after the event. In
particular, the globular cluster system (GCS) of a merging satellite galaxy may
remain as a distinct sub-population within the GCS of a massive galaxy. Using
the latest available globular cluster velocities and metallicities, we present
the results of a search for grouping in the GCS of our nearest large spiral
galaxy neighbor, M31. A modified friends-of-friends algorithm is used to
identify a number of possible merger remnants in projected position, radial
velocity and [Fe/H] parameter space. Numerical simulations are used to check
that such merger remnants are indeed plausible over the timescales of interest.
The identification of stellar streams associated with these groups is required
in order to confirm that they represent merger remnants.Comment: 19 pages, 3 figures, accepted for publication in the Ap
A Wide Symbiotic Channel to Type Ia Supernovae
As a promising channel to Type Ia supernovae (SNe Ia), we have proposed a
symbiotic binary system consisting of a white dwarf (WD) and a low mass
red-giant (RG), where strong winds from the accreting WD play a key role to
increase the WD mass to the Chandrasekhar mass limit. Here we propose two new
evolutionary processes which make the symbiotic channel to SNe Ia much wider.
(1) We first show that the WD + RG close binary can form from a wide binary
even with such a large initial separation as . Such
a binary consists of an AGB star and a low mass main-sequence (MS) star, where
the AGB star is undergoing superwind before becoming a WD. If the superwind at
the end of AGB evolution is as fast as or slower than the orbital velocity, the
wind outflowing from the system takes away the orbital angular momentum
effectively. As a result the wide binary shrinks greatly to become a close
binary. Therefore, the WD + RG binary can form from much wider binaries than
our earlier estimate. (2) When the RG fills its inner critical Roche lobe, the
WD undergoes rapid mass accretion and blows a strong optically thick wind. Our
earlier analysis has shown that the mass transfer is stabilized by this wind
only when the mass ratio of RG/WD is smaller than 1.15. Our new finding is that
the WD wind can strip mass from the RG envelope, which could be efficient
enough to stabilize the mass transfer even if the RG/WD mass ratio exceeds
1.15. With the above two new effects (1) and (2), the symbiotic channel can
account for the inferred rate of SNe Ia in our Galaxy.Comment: 29 pages including 14 firgures, to be published in ApJ, 521, No.
Large-scale study of the NGC 1399 globular cluster system in Fornax
We present a Washington C and Kron-Cousins R photometric study of the
globular cluster system of NGC 1399, the central galaxy of the Fornax cluster.
A large areal coverage of 1 square degree around NGC 1399 is achieved with
three adjoining fields of the MOSAIC II Imager at the CTIO 4-m telescope.
Working on such a large field, we can perform the first indicative
determination of the total size of the NGC 1399 globular cluster system. The
estimated angular extent, measured from the NGC 1399 centre and up to a
limiting radius where the areal density of blue globular clusters falls to 30
per cent of the background level, is 45 +/- 5 arcmin, which corresponds to 220
- 275 kpc at the Fornax distance. The bimodal colour distribution of this
globular cluster system, as well as the different radial distribution of blue
and red clusters, up to these large distances from the parent galaxy, are
confirmed. The azimuthal globular cluster distribution exhibits asymmetries
that might be understood in terms of tidal stripping of globulars from NGC
1387, a nearby galaxy. The good agreement between the areal density profile of
blue clusters and a projected dark-matter NFW density profile is emphasized.Comment: 9 pages, 9 figures. Accepted for publication in A&
Construction and Analysis of High-Complexity Ribosome Display Random Peptide Libraries
Random peptide libraries displayed on the ribosome are becoming a new tool for the in vitro selection of biologically relevant macromolecules, including epitopes, antagonists, enzymes, and cell-surface receptors. Ribosome display is a cell-free system of coupling individual nascent proteins (phenotypes) to their corresponding mRNA (genotypes) by the formation of stable protein-ribosome-mRNA complexes and permitting the selection of a functional nascent protein by iterative cycles of panning and reverse transcription-polymerase chain reaction (RT-PCR) amplification in vitro. The complexity of the random peptide library is critical for the success of a panning experiment; greater the diversity of sequences within the library, the more likely it is that the library comprises sequences that can bind a given target with specific affinity. Here, we have used the cell-free system Escherichia coli S30 lysate to construct high-complexity random peptide libraries (>1014 independent members) by introducing strategies that are different from the methods described by Mattheakis et al. and Lamla et al. The key step in our method is to produce nanomole (nmol) amounts of DNA elements that are necessary for in vitro transcription/translation by using PCR but not plasmid DNA. Library design strategies and protocols that facilitate rapid identification are also presented
The Kinematics and Metallicity of the M31 Globular Cluster System
With the ultimate aim of distinguishing between various models describing the
formation of galaxy halos (e.g. radial or multi-phase collapse, random
mergers), we have completed a spectroscopic study of the globular cluster
system of M31. We present the results of deep, intermediate-resolution,
fibre-optic spectroscopy of several hundred of the M31 globular clusters using
the Wide Field Fibre Optic Spectrograph (WYFFOS) at the William Herschel
Telescope in La Palma, Canary Islands. These observations have yielded precise
radial velocities (+/-12 km/s) and metallicities (+/-0.26 dex) for over 200
members of the M31 globular cluster population out to a radius of 1.5 degrees
from the galaxy center. Many of these clusters have no previous published
radial velocity or [Fe/H] estimates, and the remainder typically represent
significant improvements over earlier determinations. We present analyses of
the spatial, kinematic and metal abundance properties of the M31 globular
clusters. We find that the abundance distribution of the cluster system is
consistent with a bimodal distribution with peaks at [Fe/H] = -1.4 and -0.5.
The metal-rich clusters demonstrate a centrally concentrated spatial
distribution with a high rotation amplitude, although this population does not
appear significantly flattened and is consistent with a bulge population. The
metal-poor clusters tend to be less spatially concentrated and are also found
to have a strong rotation signature.Comment: 33 pages, 20 figure
Hyaluronic acid-conjugated lipoplexes for targeted delivery of siRNA in a murine metastatic lung cancer model.
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