269 research outputs found
Evolution of Binary Stars in Multiple-Population Globular Clusters - II. Compact Binaries
We present the results of a survey of N-body simulations aimed at exploring
the evolution of compact binaries in multiple-population globular clusters.We
show that as a consequence of the initial differences in the structural
properties of the first-generation (FG) and the second-generation (SG)
populations and the effects of dynamical processes on binary stars, the SG
binary fraction decreases more rapidly than that of the FG population. The
difference between the FG and SG binary fraction is qualitatively similar to
but quantitatively smaller than that found for wider binaries in our previous
investigations.The evolution of the radial variation of the binary fraction is
driven by the interplay between binary segregation, ionization and ejection.
Ionization and ejection counteract in part the effects of mass segregation but
for compact binaries the effects of segregation dominate and the inner binary
fraction increases during the cluster evolution. We explore the variation of
the difference between the FG and the SG binary fraction with the distance from
the cluster centre and its dependence on the binary binding energy and cluster
structural parameters. The difference between the binary fraction in the FG and
the SG populations found in our simulations is consistent with the results of
observational studies finding a smaller binary fraction in the SG population.Comment: 9 pages, 12 figures. Accepted for publication in MNRA
Evolution of Binary Stars in Multiple-Population Globular Clusters
The discovery of multiple stellar populations in globular clusters has
implications for all the aspects of the study of these stellar systems. In this
paper, by means of N-body simulations, we study the evolution of binary stars
in multiple-population clusters and explore the implications of the initial
differences in the spatial distribution of different stellar populations for
the evolution and survival of their binary stars. Our simulations show that
initial differences between the spatial distribution of first-generation (FG)
and second-generation (SG) stars can leave a fingerprint in the current
properties of the binary population. SG binaries are disrupted more efficiently
than those of the FG population resulting in a global SG binary fraction
smaller than that of the FG. As for surviving binaries, dynamical evolution
produces a difference between the SG and the FG binary binding energy
distribution with the SG population characterized by a larger fraction of high
binding energy (more bound) binaries. We have also studied the dependence of
the binary properties on the distance from the cluster centre. Although the
global binary fraction decreases more rapidly for the SG population, the local
binary fraction measured in the cluster inner regions may still be dominated by
SG binaries. The extent of the differences between the surviving FG and SG
binary binding energy distribution also varies radially within the cluster and
is larger in the cluster inner regions.Comment: 10 pages, 12 figures. Accepted for publication in MNRA
Decoupled and inhomogeneous gas flows in S0 galaxies
A recent analysis of the "Einstein" sample of early-type galaxies has
revealed that at any fixed optical luminosity Lb S0 galaxies have lower mean
X-ray luminosity Lx per unit Lb than ellipticals. Following a previous
analytical investigation of this problem (Ciotti & Pellegrini 1996), we have
performed 2D numerical simulations of the gas flows inside S0 galaxies in order
to ascertain the effectiveness of rotation and/or galaxy flattening in reducing
the Lx/Lb ratio. The flow in models without SNIa heating is considerably
ordered, and essentially all the gas lost by the stars is cooled and
accumulated in the galaxy center. If rotation is present, the cold material
settles in a disk on the galactic equatorial plane. Models with a time
decreasing SNIa heating host gas flows that can be much more complex. After an
initial wind phase, gas flows in energetically strongly bound galaxies tend to
reverse to inflows. This occurs in the polar regions, while the disk is still
in the outflow phase. In this phase of strong decoupling, cold filaments are
created at the interface between inflowing and outflowing gas. Models with more
realistic values of the dynamical quantities are preferentially found in the
wind phase with respect to their spherical counterparts of equal Lb. The
resulting Lx of this class of models is lower than in spherical models with the
same Lb and SNIa heating. At variance with cooling flow models, rotation is
shown to have only a marginal effect in this reduction, while the flattening is
one of the driving parameters for such underluminosity, in accordance with the
analytical investigation.Comment: 32 pages LaTex file, plus 5 .ps figures and macro aasms4.sty --
Accepted on Ap
Neck paraganglioma and follicular lymphoma: A case report
Background: Paragangliomas and pheochromocytomas are sympathetic or parasympathetic tumors derived from the paraganglia and the adrenal medulla, respectively. Paragangliomas and pheochromocytomas can be sporadic or familial, the latter frequently being multifocal and possibly due to succinate dehydrogenase complex genes mutations. In addition, 12% of sporadic paragangliomas are related to covered succinate dehydrogenase complex mutations. The importance of identifying succinate dehydrogenase complex mutations is related to the risk for these patients of developing multiple tumors, including non-endocrine ones, showing an aggressive clinical presentation. Case presentation: We report the case of a 45-year-old Caucasian man with an indolent mass in his neck. Ultrasound of his neck, magnetic resonance imaging, and 1,4,7,10-tetraazacyclododecane-N(I),N(II),N(III),N(IIII)-tetraacetic acid(D)-Phe(1)-thy(3)-octreotide (68Ga-DOTATOC) positron emission tomography-computed tomography and endocrine work-up were consistent with a carotid body paraganglioma with concomitant nodal enlargement in several body regions, which turned out to be a follicular lymphoma at histology. He was found to carry a germline Succinate dehydrogenase subunit B gene (SDHB) mutation. Conclusion: It is crucial to look for a second malignancy in the case of a paraganglioma demonstrating succinate dehydrogenase complex germline mutations
The chemical composition of red giants in 47 Tucanae I: Fundamental parameters and chemical abundance patterns
Context: The study of chemical abundance patterns in globular clusters is of
key importance to constrain the different candidates for intra-cluster
pollution of light elements. Aims: We aim at deriving accurate abundances for a
large range of elements in the globular cluster 47 Tucanae (NGC 104) to add new
constraints to the pollution scenarios for this particular cluster, expanding
the range of previously derived element abundances. Methods: Using tailored 1D
LTE atmospheric models together with a combination of equivalent width
measurements, LTE, and NLTE synthesis we derive stellar parameters and element
abundances from high-resolution, high signal-to-noise spectra of 13 red giant
stars near the tip of the RGB. Results: We derive abundances of a total 27
elements (O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr,
Mo, Ru, Ba, La, Ce, Pr, Nd, Eu, Dy). Departures from LTE were taken into
account for Na, Al and Ba. We find a mean [Fe/H] = and
in good agreement with previous studies. The
remaining elements show good agreement with the literature, but the inclusion
of NLTE for Al has a significant impact on the behaviour of this key element.
Conclusions: We confirm the presence of an Na-O anti-correlation in 47 Tucanae
found by several other works. Our NLTE analysis of Al shifts the [Al/Fe] to
lower values, indicating that this may be overestimated in earlier works. No
evidence for an intrinsic variation is found in any of the remaining elements.Comment: 22 pages, 16 figures. Accepted for publication in A&
Paving the way for the JWST: witnessing globular cluster formation at z>3
We report on five compact, extremely young (<10Myr) and blue (\beta_UV<-2.5,
F_\lambda =\lambda^\beta) objects observed with VLT/MUSE at redshift 3.1169,
3.235, in addition to three objects at z=6.145. These sources are magnified by
the Hubble Frontier Field galaxy clusters MACS~J0416 and AS1063. Their
de-lensed half light radii (Re) are between 16 to 140pc, the stellar masses are
~1-20 X 10^6 Msun, the magnitudes are m_uv=28.8 - 31.4 (-17<Muv<-15) and
specific star formation rates can be as large as ~800Gyr^-1. Multiple images of
these systems are widely separated in the sky (up to 50'') and individually
magnified by factors 3-40. Remarkably, the inferred physical properties of two
objects are similar to those expected in some globular cluster formation
scenarios, representing the best candidate proto-globular clusters (proto-GC)
discovered so far. Rest-frame optical high dispersion spectroscopy of one of
them at z=3.1169 yields a velocity dispersion \sigma_v~20km/s, implying a
dynamical mass dominated by the stellar mass. Another object at z=6.145, with
de-lensed Muv ~ -15.3 (m_uv ~ 31.4), shows a stellar mass and a star-formation
rate surface density consistent with the values expected from popular GC
formation scenarios. An additional star-forming region at z=6.145, with
de-lensed m_uv ~ 32, a stellar mass of 0.5 X 10^6 Msun and a star formation
rate of 0.06 Msun/yr is also identified. These objects currently represent the
faintest spectroscopically confirmed star-forming systems at z>3, elusive even
in the deepest blank fields. We discuss how proto-GCs might contribute to the
ionization budget of the universe and augment Lya visibility during
reionization. This work underlines the crucial role of JWST in characterizing
the rest-frame optical and near-infrared properties of such low-luminosity
high-z objects.Comment: 19 pages, 9 figures, 2 tables. MNRAS, version accepted by the refere
Perception of nurses’ professional identity during the first wave of COVID-19 pandemic infections
Background and aim of the work: The main purpose of this study is to investigate on the experience of nurses working in the Covid-19 area focusing on their role’s perception. In particular, we explored the nurses’ perception of job satisfaction in relation to the images sent back by public opinion through the mass media and social communication channels. During the first wave of Covid-19 nurses have acquired media visibility, but their feeling is represented more by the discomfort of finding themselves suddenly glorified in the face of a lack of professional, social, and economic recognition. Materials and methods: A Mix-Method methodology and convenience sampling was adopted, on the population of professionals and students in post-graduate specializations, belonging to the Department of Medicine and Surgery of the University of Parma, and by nurses from the ASST-Bergamo Est, Lombardia Italy, who worked in the Covid emergency during the first wave of the pandemic, from February 2020 to May 2020. In the quantitative phase Stamm’s Professional Quality of Life Scale - ProQOL was administered to 89 respondents through a Google Form, In the qualitative phase, 3 Focus Groups were conducted on a total of 17 students. Results: At the ProQOL questionnaire, a moderate score was found in the Compassion Satisfaction scale (CF = 38.28) and in the Secondary Traumatic Stress subscale (STS-24.33), while low values emerged in the Burnout subscale (BO = 16.02). Five specific topics emerged from the focus groups: Professional collaboration, Job satisfaction, Nurse’s personal skills, Failure to protect the public image and the nursing profession. Conclusions: The professional collaboration, union with the work team, sense of solidarity, job satisfaction, professional growth, and awareness of one’s role seem to have worked favorably on Compassion Satisfaction, while keeping Compassion Fatigue levels under control
Abundance patterns of multiple populations in Globular Clusters: a chemical evolution model based on yields from AGB ejecta
A large number of spectroscopic studies have provided evidence of the
presence of multiple populations in globular clusters by revealing patterns in
the stellar chemical abundances. This paper is aimed at studying the origin of
these abundance patterns. We explore a model in which second generation (SG)
stars form out of a mix of pristine gas and ejecta of the first generation of
asymptotic giant branch stars. We first study the constraints imposed by the
spectroscopic data of SG stars in globular clusters on the chemical properties
of the asymptotic and super asymptotic giant branch ejecta. With a simple
one-zone chemical model, we then explore the formation of the SG population
abundance patterns focussing our attention on the Na-O, Al-Mg anticorrelations
and on the helium distribution function. We carry out a survey of models and
explore the dependence of the final SG chemical properties on the key
parameters affecting the gas dynamics and the SG formation process. Finally, we
use our chemical evolution framework to build specific models for NGC 2808 and
M4, two Galactic globular clusters which show different patterns in the Na-O
and Mg-Al anticorrelation and have different helium distributions. We find that
the amount of pristine gas involved in the formation of SG stars is a key
parameter to fit the observed O-Na and Mg-Al patterns. The helium distribution
function for these models is in general good agreement with the observed one.
Our models, by shedding light on the role of different parameters and their
interplay in determining the final SG chemical properties, illustrate the basic
ingredients, constraints and problems encountered in this self-enrichment
scenario which must be addressed by more sophisticated chemical and
hydrodynamic simulations.Comment: 19 pages, 10 figures, MNRAS accepte
Insulin-Like Growth Factor-1 Inhibits Mature Oligodendrocyte Apoptosis during Primary Demyelination
Metabolic insult results in apoptosis and depletion of mature oligodendrocytes during demyelination. To examine the role of insulin-like growth factor-1 (IGF-1) during acute demyelination and remyelination in the adult CNS, we exposed transgenic mice that continuously express IGF-1
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