600 research outputs found
The Gradients in the 47 Tuc Red Giant Branch Bump and Horizontal Branch are Consistent With a Centrally-Concentrated, Helium-Enriched Second Stellar Generation
We combine ground and space-based photometry of the Galactic globular cluster
47 Tuc to measure four independent lines of evidence for a helium gradient in
the cluster, whereby stars in the cluster outskirts would have a lower initial
helium abundance than stars in and near the cluster core. First and second, we
show that the red giant branch bump (RGBB) stars exhibit gradients in their
number counts and brightness. With increased separation from the cluster
center, they become more numerous relative to the other red giant (RG) stars.
They also become fainter. For our third and fourth lines of evidence, we show
that the horizontal branch (HB) of the cluster becomes both fainter and redder
for sightlines farther from the cluster center. These four results are
respectively detected at the 2.3, 3.6, 7.7 and
4.1 levels. Each of these independent lines of evidence is found to be
significant in the cluster-outskirts; closer in, the data are more compatible
with uniform mixing. Our radial profile is qualitatively consistent with but
quantitatively tighter than previous results based on CN absorption. These
observations are qualitatively consistent with a scenario wherein a second
generation of stars with modestly enhanced helium and CNO abundance formed deep
within the gravitational potential of a cluster of previous generation stars
having more canonical abundances.Comment: 20 pages, 6 figures, 1 table, submitted to The Astrophysical Journa
D010 Mesenchymal stem cells protect cardiomyocytes from reperfusion injury through a paracrine activation of the PI3 kinase pathway
ObjectivesPrevious data suggest that implantation of mesenchymal stem cells (MSCs) improves heart function after myocardial infarction. We investigated whether protection afforded by MSCs might involve a paracrine activation of the PI3 kinase pathway in reperfused cardiomyocytes.MethodMSCs and neonatal rat cardiomyocytes (NRCs) were isolated and cultured separately. NRCs (2.106) were subjected to 5 hours of ischemia followed by 16 hours of reperfusion. At the time of reperfusion, NRCs (n=8-14/group) received either fresh medium (control group), or the following treatments: MSCs (2.105 MSCs in fresh medium), conditioned SN (MSCs supernatant alone (i.e. without MSCs) obtained after 8 hours of serum deprived culture), [conditioned SN + LY294002] (15 microM of LY294002 a specifi c inhibitor of PI3K), [conditioned SN + Wortmannin] (100 nM of wortmannin, a non specifi c inhibitor of PI3K), or CsA (200 nM in fresh medium) a potent inhibitor of the mitochondrial permeability transition pore. Cell death was assessed by LDH release in NRCs supernatant at the end of reperfusion.ResultsAs expected, LDH activity was dramatically reduced by CsA, averaging 4 % of control values. LDH activity was signifi cantly reduced by MSCs alone and by conditioned SN, averaging 29 % and 12 % of control value, respectively. Both LY294002 and wortmannin signifi cantly attenuated conditioned SN induced protection.Conclusionour data suggest that MSCs can protect NRCs from reperfusion injury through a paracrine activation of the PI3K pathway
Elastic anomalies associated with domain switching in BaTiO3 single crystals under in situ electrical cycling
The elastic response of BaTiO3 single crystals during electric field cycling at room temperature has been studied using in situ Resonant Ultrasound Spectroscopy (RUS), which allows monitoring of both the elastic and anelastic changes caused by ferroelectric polarization switching. We find that the first ferroelectric switching of a virgin single crystal is dominated by ferroelastic 90° switching. In subsequent ferroelectric switching, ferroelastic switching is reduced by domain pinning and by the predominance of 180° ferroelectric domains, as confirmed by polarized light microscopy. RUS under in situ electric field therefore demonstrates to be an effective technique for the investigation of electromechanical coupling in ferroelectrics
Mapping the X-Shaped Milky Way Bulge
We analyzed the distribution of the RC stars throughout Galactic bulge using
2MASS data. We mapped the position of the red clump in 1 sq.deg. size fields
within the area |l|<=8.5deg and l=0 deg axis. Crude
measurements of the space densities of RC stars in the bright and faint RC
populations are consistent with the adopted RC distances, providing further
supporting evidence that the X-structure is real, and that there is approximate
front-back symmetry in our bulge fields. We conclude that the Milky Way bulge
has an X-shaped structure within $|l|<~2deg, seen almost edge on with respect
to the line of sight. Additional deep NIR photometry extending into the
innermost bulge regions combined with spectroscopic data is needed in order to
discriminate among the different possibilities that can cause the observed
X-shaped structure.Comment: 9 pages, 5 figures, accepted for publication in A
The Magellanic Edges Survey I. Description and First Results
We present an overview of, and first science results from, the Magellanic
Edges Survey (MagES), an ongoing spectroscopic survey mapping the kinematics of
red clump and red giant branch stars in the highly substructured periphery of
the Magellanic Clouds. In conjunction with Gaia astrometry, MagES yields a
sample of ~7000 stars with individual 3D velocities that probes larger
galactocentric radii than most previous studies. We outline our target
selection, observation strategy, data reduction and analysis procedures, and
present results for two fields in the northern outskirts ( on-sky
from the centre) of the Large Magellanic Cloud (LMC). One field, located in the
vicinity of an arm-like overdensity, displays apparent signatures of
perturbation away from an equilibrium disk model. This includes a large radial
velocity dispersion in the LMC disk plane, and an asymmetric line-of-sight
velocity distribution indicative of motions vertically out of the disk plane
for some stars. The second field reveals 3D kinematics consistent with an
equilibrium disk, and yields km s at a
radial distance of ~10.5kpc from the LMC centre. This leads to an enclosed mass
estimate for the LMC at this radius of
.Comment: 23 pages, 10 figures. Accepted by MNRA
The origin of the split red clump in the Galactic bulge of the Milky Way
Near the minor axis of the Galactic bulge, at latitudes b < -5 degrees, the
red giant clump stars are split into two components along the line of sight. We
investigate this split using the three fields from the ARGOS survey that lie on
the minor axis at (l,b) = (0,-5), (0,-7.5), (0,-10) degrees. The separation is
evident for stars with [Fe/H] > -0.5 in the two higher-latitude fields, but not
in the field at b = -5 degrees. Stars with [Fe/H] < -0.5 do not show the split.
We compare the spatial distribution and kinematics of the clump stars with
predictions from an evolutionary N-body model of a bulge that grew from a disk
via bar-related instabilities. The density distribution of the peanut-shaped
model is depressed near its minor axis. This produces a bimodal distribution of
stars along the line of sight through the bulge near its minor axis, very much
as seen in our observations. The observed and modelled kinematics of the two
groups of stars are also similar. We conclude that the split red clump of the
bulge is probably a generic feature of boxy/peanut bulges that grew from disks,
and that the disk from which the bulge grew had relatively few stars with
[Fe/H] < -0.5Comment: 12 pages, 9 figures, accepted for publication in Ap
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