3,257 research outputs found
Galactic Cosmic Rays from Superbubbles and the Abundances of Lithium, Beryllium, and Boron
In this article we study the galactic evolution of the LiBeB elements within
the framework of a detailed model of the chemical evolution of the Galaxy that
includes galactic cosmic ray nucleosynthesis by particles accelerated in
superbubbles. The chemical composition of the superbubble consists of varying
proportions of ISM and freshly supernova synthesized material. The
observational trends of 6 LiBeB evolution are nicely reproduced by models in
which GCR come from a mixture of 25% of supernova material with 75% of ISM,
except for 6 Li, for which maybe an extra source is required at low
metallicities. To account for 7 Li evolution several additional sources have
been considered (neutrino-induced nucleosynthesis, nova outbursts, C-stars).
The model fulfills the energetic requirements for GCR acceleration.Comment: 25 pages, 9 figures. Accepted for publication in the Astrophysical
Journa
Properties of carbon stars in the Solar neighbourhood based on Gaia DR2 astrometry
We find that the combined LF of N- and SC-type stars are consistent with a
Gaussian distribution peaking at M_bol~ -5.2 mag. The resulting LF however
shows two tails at lower and higher luminosities more extended than those
previously found, indicating that AGB carbon stars with Solar metallicity may
reach M_bol~-6.0 mag. We find that J-type stars are about half a magnitude
fainter on average than N- and SC-type stars, while R-hot stars are half a
magnitude brighter than previously found. The Galactic spatial distribution and
velocity components of the N-, SC- and J-type stars are very similar, while
about 30 % of the R-hot stars in the sample are located at distances larger
than ~ 500 pc from the Galactic Plane, and show a significant drift with
respect to the local standard of rest. The LF derived for N- and SC-type in the
Solar neighbourhood fully agrees with the expected luminosity of stars of 1.5-3
M_o on the AGB. On a theoretical basis, the existence of an extended low
luminosity tail would require a contribution of extrinsic low mass carbon
stars, while the high luminosity one would imply that stars with mass up to ~5
Mo may become carbon star on the AGB. J-type stars not only differ
significantly in their chemical composition with respect to the N- and SC-types
but also in their LF, which reinforces the idea that these carbon stars belong
to a dvifferent type whose origin is still unknown. The derived luminosities of
R-hot stars make these stars unlikely to be in the red-clump as previously
claimed. On the other hand, the derived spatial distribution and kinematic
properties, together with their metallicity, indicate that most of the N-, SC-
and J-type stars belong to the thin disc population, while a significant
fraction of R-hot stars show characteristics compatible with the thick disc.Comment: Accepted in Astronomy & Astrophysic
Olive oil and postprandial hyperlipidemia: implications for atherosclerosis and metabolic syndrome
42 Páginas; 4 Tablas; 6 FigurasOlive oil is the primary source of fat in the Mediterranean diet, which is associated with a significant improvement in health status, as measured by reduced mortality from several chronic diseases. The current pandemic of obesity, metabolic syndrome, and type 2 diabetes is intimately associated with an atherogenic dyslipidemic phenotype. The core components of the dyslipidemia of the metabolic syndrome, which most likely initiate atherosclerosis, are the “lipid triad” consisting of high plasma triglycerides, low levels of high-density lipoproteins, and a preponderance of small, dense low-density lipoproteins at fasting. However, postprandial (non-fasting) TGs (postprandial hyperlipidemia) are also recognized as an important component for atherosclerosis. Herein, the purpose of this review was to provide an update on the effects and mechanisms related to olive oil on postprandial hyperlipidemia and its implications for the onset and progression of atherosclerosis and metabolic syndrome.This study was supported by research Grant AGL2011-29008 (Spanish Ministry of Science and Innovation, MICINN). S. M. has the benefit of a FPI fellowship (BES-2012-056104) of MICINN. B. B. and S. L. acknowledge financial support from “V Own Research Plan” (University of Seville) and the Spanish Research Council (CSIC)/Juan de la Cierva, respectively.Peer reviewe
Comparative Modelling of the Spectra of Cool Giants
Our ability to extract information from the spectra of stars depends on
reliable models of stellar atmospheres and appropriate techniques for spectral
synthesis. Various model codes and strategies for the analysis of stellar
spectra are available today. We aim to compare the results of deriving stellar
parameters using different atmosphere models and different analysis strategies.
The focus is set on high-resolution spectroscopy of cool giant stars. Spectra
representing four cool giant stars were made available to various groups and
individuals working in the area of spectral synthesis, asking them to derive
stellar parameters from the data provided. The results were discussed at a
workshop in Vienna in 2010. Most of the major codes currently used in the
astronomical community for analyses of stellar spectra were included in this
experiment. We present the results from the different groups, as well as an
additional experiment comparing the synthetic spectra produced by various codes
for a given set of stellar parameters. Similarities and differences of the
results are discussed. Several valid approaches to analyze a given spectrum of
a star result in quite a wide range of solutions. The main causes for the
differences in parameters derived by different groups seem to lie in the
physical input data and in the details of the analysis method. This clearly
shows how far from a definitive abundance analysis we still are.Comment: accepted for publication in A&A. This version includes also the
online tables. Reference spectra will later be available via the CD
The Kr85 s-process Branching and the Mass of Carbon Stars
We present new spectroscopic observations for a sample of C(N)-type red
giants. These objects belong to the class of Asymptotic Giant Branch stars,
experiencing thermal instabilities in the He-burning shell (thermal pulses).
Mixing episodes called third dredge-up enrich the photosphere with newly
synthesized C12 in the He-rich zone, and this is the source of the high
observed ratio between carbon and oxygen (C/O > 1 by number). Our spectroscopic
abundance estimates confirm that, in agreement with the general understanding
of the late evolutionary stages of low and intermediate mass stars, carbon
enrichment is accompanied by the appearance of s-process elements in the
photosphere. We discuss the details of the observations and of the derived
abundances, focusing in particular on rubidium, a neutron-density sensitive
element, and on the s-elements Sr, Y and Zr belonging to the first s-peak. The
critical reaction branching at Kr85, which determines the relative enrichment
of the studied species, is discussed. Subsequently, we compare our data with
recent models for s-processing in Thermally Pulsing Asymptotic Giant Branch
stars, at metallicities relevant for our sample. A remarkable agreement between
model predictions and observations is found. Thanks to the different neutron
density prevailing in low and intermediate mass stars, comparison with the
models allows us to conclude that most C(N) stars are of low mass (M < 3Mo). We
also analyze the C12/C13 ratios measured, showing that most of them cannot be
explained by canonical stellar models. We discuss how this fact would require
the operation of an ad hoc additional mixing, currently called Cool Bottom
Process, operating only in low mass stars during the first ascent of the red
giant branch and, perhaps, also during the asymptotic giant branch.Comment: 54 pages + 6 figures + 6 tables. ApJ accepte
Chemical analysis of carbon stars in the Local Group: I. The Small Magellanic Cloud and the Sagittarius dwarf spheroidal galaxy
We present the first results of our ongoing chemical study of carbon stars in
the Local Group of galaxies. We used spectra obtained with UVES at the 8.2 m
Kueyen-VLT telescope and a new grid of spherical model atmospheres for cool
carbon-rich stars which include polyatomic opacities, to perform a full
chemical analysis of one carbon star, BMB-B~30, in the Small Magellanic Cloud
(SMC) and two, IGI95-C1 and IGI95-C3, in the Sagittarius Dwarf Spheroidal (Sgr
dSph) galaxy. Our main goal is to test the dependence on the stellar
metallicity of the s-process nucleosynthesis and mixing mechanism occurring in
AGB stars. For these three stars, we find important s-element enhancements with
respect to the mean metallicity ([M/H]), namely [s/M]+1.0, similar to
the figure found in galactic AGB stars of similar metallicity. The abundance
ratios derived between elements belonging to the first and second s-process
abundance peaks, corresponding to nuclei with a magic number of neutrons N=50
(88Sr, 89Y, 90Zr) and N=82 (138Ba, 139La, 140Ce, 141Pr), agree remarkably well
with the theoretical predictions of low mass (M ~M) metal-poor AGB
nucleosynthesis models where the main source of neutrons is the
CO reaction activated duringthe long interpulse phase,
in a small pocket located within the He-rich intershell. The derived C/O and
C/C ratios are, however, more difficult to reconcile with
theoretical expectations. Possible explanations, like the extrinsic origin of
the composition of these carbon stars or the operation of a non-standard mixing
process during the AGB phase (such as the {\it cool bottom process}), are
discussed on the basis of the collected observational constraints
Phenomenology of the nMSSM from colliders to cosmology
Low energy supersymmetric models provide a solution to the hierarchy problem
and also have the necessary ingredients to solve two of the most outstanding
issues in cosmology: the origin of dark matter and baryonic matter. One of the
most attractive features of this framework is that the relevant physical
processes are related to interactions at the weak scale and therefore may be
tested in collider experiments in the near future. This is true for the Minimal
Supersymmetric Standard Model (MSSM) as well as for its extension with the
addition of one singlet chiral superfield, the so-called nMSSM. It has been
recently shown that within the nMSSM an elegant solution to both the problem of
baryogenesis and dark matter may be found, that relies mostly on the mixing of
the singlet sector with the Higgs sector of the theory. In this work we review
the nMSSM model constraints from cosmology and present the associated collider
phenomenology at the LHC and the ILC. We show that the ILC will efficiently
probe the neutralino, chargino and Higgs sectors, allowing to confront
cosmological observations with computations based on collider measurements. We
also investigate the prospects for a direct detection of dark matter and the
constraints imposed by the current bounds of the electron electric dipole
moment in this model.Comment: 44 pp, 10 figures; Fig.9 replaced; discussion on CP violation
extended and references added; few minor additions in text about details of
the cut
s-Process Nucleosynthesis in Carbon Stars
We present the first detailed and homogeneous analysis of the s-element
content in Galactic carbon stars of N-type. Abundances of Sr,Y, Zr (low-mass
s-elements, or ls) and of Ba, La, Nd, Sm and Ce (high-mass s-elements, hs) are
derived using the spectral synthesis technique from high-resolution spectra.
The N-stars analyzed are of nearly solar metallicity and show moderate
s-element enhancements, similar to those found in S stars, but smaller than
those found in the only previous similar study (Utsumi 1985), and also smaller
than those found in supergiant post-AGB stars. This is in agreement with the
present understanding of the envelope s-element enrichment in giant stars,
which is increasing along the spectral sequence M-->MS-->S-->SC-->C during the
AGB phase. We compare the observational data with recent -process
nucleosynthesis models for different metallicities and stellar masses. Good
agreement is obtained between low mass AGB star models (M < 3 M_o) and
s-elements observations. In low mass AGB stars, the 13C(alpha, n)16O reaction
is the main source of neutrons for the s-process; a moderate spread, however,
must exist in the abundance of 13C that is burnt in different stars. By
combining information deriving from the detection of Tc, the infrared colours
and the theoretical relations between stellar mass, metallicity and the final
C/O ratio, we conclude that most (or maybe all) of the N-stars studied in this
work are intrinsic, thermally-pulsing AGB stars; their abundances are the
consequence of the operation of third dredge-up and are not to be ascribed to
mass transfer in binary systems.Comment: 31 pages, 10 figures, 6 tables. Accepted in Ap
Decoupling property of the supersymmetric Higgs sector with four doublets
In supersymmetric standard models with multi Higgs doublet fields,
selfcoupling constants in the Higgs potential come only from the D-terms at the
tree level. We investigate the decoupling property of additional two heavier
Higgs doublet fields in the supersymmetric standard model with four Higgs
doublets. In particular, we study how they can modify the predictions on the
quantities well predicted in the minimal supersymmetric standard model (MSSM),
when the extra doublet fields are rather heavy to be measured at collider
experiments. The B-term mixing between these extra heavy Higgs bosons and the
relatively light MSSM-like Higgs bosons can significantly change the
predictions in the MSSM such as on the masses of MSSM-like Higgs bosons as well
as the mixing angle for the two light CP-even scalar states. We first give
formulae for deviations in the observables of the MSSM in the decoupling region
for the extra two doublet fields. We then examine possible deviations in the
Higgs sector numerically, and discuss their phenomenological implications.Comment: 26 pages, 24 figures, text sligtly modified,version to appear in
Journal of High Energy Physic
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