206 research outputs found
2MASS NIR photometry for 693 candidate globular clusters in M31 and the Revised Bologna Catalogue
We have identified in the 2MASS database 693 known and candidate globular
clusters in M31. The 2MASS J,H,K magnitudes of these objects have been
transformed to the same homogeneous photometric system of existing near
infrared photometry of M31 globulars, finally yielding J,H,K integrated
photometry for 279 confirmed M31 clusters, 406 unconfirmed candidates and 8
objects with controversial classification. Of these objects 529 lacked any
previous estimate of their near infrared magnitudes. The newly assembled near
infrared dataset has been implemented into a revised version of the Bologna
Catalogue of M31 globulars, with updated optical (UBVRI) photometry taken, when
possible, from the most recent sources of CCD photometry available in the
literature and transformed to a common photometric system. The final Revised
Bologna Catalogue (available in electronic form) is the most comprehensive list
presently available of confirmed and candidate M31 globular clusters, with a
total of 1164 entries. In particular, it includes 337 confirmed GCs, 688 GC
candidates, 10 objects with controversial classification, 70 confirmed
galaxies, 55 confirmed stars, and 4 HII regions lying within ~3 deg. from the
center of the M31 galaxy. Using the newly assembled database we show that the
V-K color provides a powerful tool to discriminate between M31 clusters and
background galaxies, and we identify a sample of 83 globular cluster
candidates, which is not likely to be contaminated by misclassified galaxies.Comment: 9 pages,5 figures,accepted for publication in Astronomy &
Astrophysics ASCII (commented) version of the tables 2,3,4 are available at
http://www.bo.astro.it/M3
Integrated Colours of Milky Way Globular Clusters and Horizontal Branch Morphology
Broadband colours are often used as metallicity proxies in the study of
extragalactic globular clusters. A common concern is the effect of variations
in horizontal branch (HB) morphology--the second-parameter effect--on such
colours. We have used UBVI, Washington, and DDO photometry for a compilation of
over 80 Milky Way globular clusters to address this question. Our method is to
fit linear relations between colour and [Fe/H], and study the correlations
between the residuals about these fits and two quantitative measures of HB
morphology. While there is a significant HB effect seen in U-B, for the
commonly used colours B-V, V-I, and C-T_1, the deviations from the baseline
colour-[Fe/H] relations are less strongly related to HB morphology. There may
be weak signatures in B-V and C-T_1, but these are at the limit of
observational uncertainties. The results may favour the use of B-I in studies
of extragalactic globular clusters, especially when its high [Fe/H]-sensitivity
is considered.Comment: 19 pages, including 26 figures. AN in press. Figure 9 stubbornly
resists attempts to correct i
Detection of a Thick Disk in the edge-on Low Surface Brightness Galaxy ESO 342-G017: I. VLT Photometry in V and R Bands
We report the detection of a thick disk in the edge-on, low surface
brightness (LSB), late-type spiral ESO 342-G017, based on ultra-deep images in
the V and R bands obtained with the VLT Test Camera during Science Verification
on UT1. All steps in the reduction procedure are fully described, which,
together with an extensive analysis of systematic and statistic uncertainties,
has resulted in surface brightness photometry that is reliable for the
detection of faint extended structure to a level of V = 27.5 and R = 28.5
mag/square arcsec. The faint light apparent in these deep images is
well-modeled by a thick exponential disk with an intrinsic scale height about
2.5 times that of the thin disk, and a comparable or somewhat larger scale
length. Deprojection including the effects of inclination and convolution with
the PSF allow us to estimate that the thick disk contributes 20-40% of the
total (old) stellar disk luminosity of ESO 342-G017. To our knowledge, this is
the first detection of a thick disk in an LSB galaxy, which are generally
thought to be rather unevolved compared to higher surface brightness galaxies.Comment: Accepted for publication in Astronomy & Astrophysics; 18 pages, 12
figure
A Quantitative Link Between Globular Clusters and the Stellar Halos in Elliptical Galaxies
This paper explores the quantitative connection between globular clusters and
the diffuse stellar population of the galaxies they are associated with. Both
NGC 1399 and NGC 4486 (M87) are well suited for this kind of analysis due to
their large globular cluster populations. The main assumption of our Monte
Carlo based models is that each globular cluster is formed along with a given
diffuse stellar mass that shares the same spatial distribution, chemical
composition and age. The main globular clusters subpopulations, that determine
the observed bimodal colour distribution, are decomposed avoiding a priori
parametric (e.g. Gaussian) fits and using a new colour (C-T1)-metallicity
relation. The eventual detectability of a blue tilt in the colour magnitude
diagrams of the blue globulars subpopulation is also addressed. A successful
link between globular clusters and the stellar galaxy halo is established by
assuming that the number of globular clusters per associated diffuse stellar
mass t is a function of total abundance [Z/H] and behaves as
t=gamma*exp(delta[Z/H]) (i.e. increases when abundance decreases).Comment: 19 pages, 24 figures and 4 tables. Accepted for publication in MNRA
The velocity dispersion and mass-to-light ratio of the remote halo globular cluster NGC 2419
Precise radial velocity measurements from HIRES on the Keck I telescope are
presented for 40 stars in the outer halo globular cluster NGC 2419. These data
are used to probe the cluster's stellar mass function and search for the
presence of dark matter in this cluster. NGC 2419 is one of the best Galactic
globular clusters for such a study due to its long relaxation time (T_{r0} ~
10^{10} yr) and large Galactocentric distance (R_{GC} ~ 90 kpc) -- properties
that make significant evolutionary changes in the low-mass end of the cluster
mass function unlikely. We find a mean cluster velocity of =-20.3 +- 0.7
km/sec and an internal velocity dispersion of \sigma = 4.14 +- 0.48 km/sec,
leading to a total mass of (9.0 +- 2.2) * 10^5 Msun and a global mass-to-light
ratio of M/L_V = 2.05 +- 0.50 in solar units. This mass-to-light ratio is in
good agreement with what one would expect for a pure stellar system following a
standard mass function at the metallicity of NGC 2419. In addition, the
mass-to-light ratio does not appear to rise towards the outer parts of the
cluster. Our measurements therefore rule out the presence of a dark matter halo
with mass larger than ~10^7 Msun inside the central 500 pc, which is lower than
what is found for the central dark matter densities of dSph galaxies. We also
discuss the relevance of our measurements for alternative gravitational
theories such as MOND, and for possible formation scenarios of ultra-compact
dwarf galaxies.Comment: 11 pages, 7 figures, MNRAS in pres
Human annexin A6 interacts with influenza a virus protein M2 and negatively modulates infection
Copyright © 2012, American Society for Microbiology. All Rights ReservedThe influenza A virus M2 ion channel protein has the longest cytoplasmic tail (CT) among the three viral envelope proteins and is well conserved between different viral strains. It is accessible to the host cellular machinery after fusion with the endosomal membrane and during the trafficking, assembly, and budding processes. We hypothesized that identification of host cellular interactants of M2 CT could help us to better understand the molecular mechanisms regulating the M2-dependent stages of the virus life cycle. Using yeast two-hybrid screening with M2 CT as bait, a novel interaction with the human annexin A6 (AnxA6) protein was identified, and their physical interaction was confirmed by coimmunoprecipitation assay and a colocalization study of virus-infected human cells. We found that small interfering RNA (siRNA)-mediated knockdown of AnxA6 expression significantly increased virus production, while its overexpression could reduce the titer of virus progeny, suggesting a negative regulatory role for AnxA6 during influenza A virus infection. Further characterization revealed that AnxA6 depletion or overexpression had no effect on the early stages of the virus life cycle or on viral RNA replication but impaired the release of progeny virus, as suggested by delayed or defective budding events observed at the plasma membrane of virus-infected cells by transmission electron microscopy. Collectively, this work identifies AnxA6 as a novel cellular regulator that targets and impairs the virus budding and release stages of the influenza A virus life cycle.This work was supported by the Research Fund for the Control of Infectious Disease (project 09080892) of the Hong Kong Government, the Area of Excellence Scheme of the University Grants Committee (grant
AoE/M-12/-06 of the Hong Kong Special Administrative Region, China), the French Ministry of Health, the RESPARI Pasteur Network
Age Estimations of M31 Globular Clusters from Their Spectral Energy Distributions
This paper presents accurate spectral energy distributions (SEDs) of 16 M31
globular clusters (GCs) confirmed by spectroscopy and/or high
spatial-resolution imaging, as well as 30 M31 globular cluster candidates
detected by Mochejska et al. Most of these candidates have m_V > 18, deeper
than previous searches, and these candidates have not yet been confirmed to be
globular clusters. The SEDs of these clusters and candidates are obtained as
part of the BATC Multicolor Survey of the Sky, in which the
spectrophotometrically-calibrated CCD images of M31 in 13 intermediate-band
filters from 4000 to 10000 A were observed. These filters are specifically
designed to exclude most of the bright and variable night-sky emission lines
including the OH forest. In comparison to the SEDs of true GCs, we find that
some of the candidate objects are not GCs in M31. SED fits show that
theoretical simple stellar population (SSP) models can fit the true GCs very
well. We estimate the ages of these GCs by comparing with SSP models. We find
that, the M31 clusters range in age from a few ten Myr to a few Gyr old, as
well as old GCs, confirming the conclusion that has been found by Barmby et a,
Williams & Hodge, Beasley et al., Burstein et al. and Puzia et al. in their
investigations of the SEDs of M31 globular clusters.Comment: Accepted for Publication in A&Ap, 13 pages, 6 figure
Globular cluster luminosity function as distance indicator
Globular clusters are among the first objects used to establish the distance
scale of the Universe. In the 1970-ies it has been recognized that the
differential magnitude distribution of old globular clusters is very similar in
different galaxies presenting a peak at M_V ~ -7.5. This peak magnitude of the
so-called Globular Cluster Luminosity Function has been then established as a
secondary distance indicator. The intrinsic accuracy of the method has been
estimated to be of the order of ~0.2 mag, competitive with other distance
determination methods. Lately the study of the Globular Cluster Systems has
been used more as a tool for galaxy formation and evolution, and less so for
distance determinations. Nevertheless, the collection of homogeneous and large
datasets with the ACS on board HST presented new insights on the usefulness of
the Globular Cluster Luminosity Function as distance indicator. I discuss here
recent results based on observational and theoretical studies, which show that
this distance indicator depends on complex physics of the cluster formation and
dynamical evolution, and thus can have dependencies on Hubble type, environment
and dynamical history of the host galaxy. While the corrections are often
relatively small, they can amount to important systematic differences that make
the Globular Cluster Luminosity Function a less accurate distance indicator
with respect to some other standard candles.Comment: Accepted for publication in Astrophysics and Space Science. Review
paper based on the invited talk at the conference "The Fundamental Cosmic
Distance Scale: State of the Art and Gaia Perspective", Naples, May 2011. (13
pages, 8 figures
The globular cluster system of NGC 1399 V. dynamics of the cluster system out to 80 kpc
(Abridged) We use the largest set of globular cluster velocities obtained so
far of any elliptical galaxy to revise and extend the previous investigations
of the dynamics of NGC 1399, the central dominant galaxy of the nearby Fornax
cluster of galaxies. Our sample now comprises velocities for almost 700 GCs
with projected galactocentric radii between 6 and 100 kpc. In addition, we use
velocities published by Bergond et al. (2007). We study the kinematics of the
metal-poor and metal-rich subpopulations and perform spherical Jeans modelling.
The most important results are: The metal-rich (red) GCs resemble the stellar
field population of NGC 1399 in the region of overlap. Both subpopulations are
kinematically distinct and do not show a smooth transition. It is not possible
to find a common dark halo which reproduces simultaneously the properties of
both subpopulations. Some velocities of blue GCs are only to be explained by
orbits with very large apogalactic distances, thus indicating a contamination
with GCs which belong to the entire Fornax cluster rather than to NGC 1399.
Stripped GCs from nearby elliptical galaxies, particularly NGC 1404, may also
contaminate the metal-poor sample. We argue in favour of a scenario in which
the majority of the blue cluster population has been accreted during the
assembly of the Fornax cluster. The red cluster population shares the dynamical
history of the galaxy itself. Therefore we recommend to use a dark halo based
on the red GCs alone. The dark halo which fits best is marginally less massive
than the halo quoted by Richtler et al. (2004). The comparison with X-ray
analyses is satisfactory in the inner regions, but without showing evidence for
a transition from a galaxy to a cluster halo, as suggested by X-ray work.Comment: 31 pages, accepted for publication in A&A. Online material will be
available from the CD
Biologising parenting:neuroscience discourse, English social and public health policy and understandings of the child
In recent years, claims about children's developing brains have become central to the formation of child health and welfare policies in England. While these policies assert that they are based on neuro-scientific discoveries, their relationship to neuroscience itself has been debated. However, what is clear is that they portray a particular understanding of children and childhood, one that is marked by a lack of acknowledgment of child personhood. Using an analysis of key government-commissioned reports and additional advocacy documents, this article illustrates the ways that the mind of the child is reduced to the brain, and this brain comes to represent the child. It is argued that a highly reductionist and limiting construction of the child is produced, alongside the idea that parenting is the main factor in child development. It is concluded that this focus on children's brains, with its accompanying deterministic perspective on parenting, overlooks children's embodied lives and this has implications for the design of children's health and welfare services
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