211 research outputs found
Disc dichotomy signature in the vertical distribution of [Mg/Fe] and the delayed gas infall scenario
The analysis of the APOGEE data suggests the existence of a clear distinction
between two sequences of disc stars in the [/Fe] vs. [Fe/H] abundance
ratio space. We aim to test if the two-infall chemical evolution models
designed to reproduce these two sequences in the solar neighbourhood are also
capable to predict the disc bimodality observed in the vertical distribution of
[Mg/Fe] in APOGEE DR16 data. Along with the predicted chemical composition of
SSPs born at different Galactic times in the solar vicinity, we provide their
maximum vertical height |zmax| above the Galactic plane computed assuming the
relation between the vertical action and stellar age in thin disc stars. The
predicted vertical distribution of the [Mg/Fe] abundance ratio is in agreement
with the one observed combining the APOGEE DR16 data and the astroNN catalogue
(stellar ages, orbital parameters) for stars younger than 8 Gyr (only
low- sequence stars). Including the high- disc component, the
dichotomy in the vertical [Mg/Fe] abundance distribution is reproduced
considering the observational cut in the Galactic height of |z| < 2 kpc.
However, our model predicts a too flat growth of the |zmax| as a function of
[Mg/Fe] for high- objects in contrast with the median values from
APOGEE data. Possible explanations for such a tension are: i) the data sample
with |z| < 2 kpc is more likely contaminated by halo stars, causing the median
values to be kinematically hotter, ii) external perturbations such as minor
mergers could have heated up the disc, and the heating of the orbits cannot be
modelled by only scattering processes. Assuming for the data a disc dissection
based on chemistry, the observed |zmax| distributions for high- and
low- sequences are in good agreement with our model predictions if we
consider in the calculation the errors in the vertical action estimates.Comment: Accepted for publication in Astronomy and Astrophysics (A&A), 17
pages, 15 figure
Cold streams of ionospheric oxygen in the plasma sheet during the CDAW-6 event of March 22, 1979
During magnetospheric substorm events, the plasma and ion composition experiments in the ISEE-1 and 2 satellites detected cold ionospheric O+ streams, moving tailwards in the near Earth magnetotail. Flow is parallel to the magnetic field lines, with drift velocity in agreement with the electric field topology obtained by mapping the model ionospheric field along the magnetic field lines. Fluctuations of the flow velocity of the streams can be related to magnetotail movements. Oscillations of the flow direction and speed with periods ranging from 5 to 10 min that suggest the presence of waves are observed. The streams are observed at all distances between 15 and 6 Re from the Earth. When averaged over 360 deg, the streams show up as a low energy peak, superimposed on the distribution of isotropic plasma sheet ions. This double-peak structure of the energy spectrum seems typical of the disturbed plasma sheet
Red Horizontal Branch stars: an asteroseismic perspective
Robust age estimates of red giant stars are now possible thanks to the
precise inference of their mass based on asteroseismic constraints. However,
there are cases where such age estimates can be highly precise yet very
inaccurate. An example is giants that have undergone mass loss or mass transfer
events that have significantly altered their mass. In this context, stars with
"apparent" ages significantly higher than the age of the Universe are
candidates as stripped stars, or stars that have lost more mass than expected,
most likely via interaction with a companion star, or because of the poorly
understood mass-loss mechanism along the red-giant branch. In this work we
identify examples of such objects among red giants observed by
, both at low ([Fe/H] ) and solar metallicity.
By modelling their structure and pulsation spectra, we find a consistent
picture confirming that these are indeed low-mass objects consisting of a He
core of and an envelope of . Moreover, we find that these stars are characterised by a rather
extreme coupling () between the pressure-mode and gravity-mode
cavities, i.e. much higher than the typical value for red clump stars,
providing thus a direct seismic signature of their peculiar structure. The
complex pulsation spectra of these objects, if observed with sufficient
frequency resolution, hold detailed information about the structural properties
of likely products of mass stripping, hence can potentially shed light on their
formation mechanism. On the other hand, our tests highlight the difficulties
associated with measuring reliably the large frequency separation, especially
in shorter datasets, with impact on the reliability of the inferred masses and
ages of low-mass Red Clump stars with e.g. K2 or TESS data.Comment: Accepted for publication in A&A Letter
An asteroseismic age estimate of the open cluster NGC 6866 using Kepler and Gaia
Asteroseismology of solar-like oscillations in giant stars allow the
derivation of their masses and radii. For members of open clusters this allows
an age estimate of the cluster which should be identical to the age estimate
from the colour-magnitude diagram, but independent of the uncertainties that
are present for that type of analysis. Thus, a more precise and accurate age
estimate can be obtained. We aim to measure asteroseismic properties of
oscillating giant members of the open cluster NGC 6866 and utilise these for a
cluster age estimate. Model comparisons allow constraints on the stellar
physics, and here we investigate the efficiency of convective-core overshoot
and effects of rotation during the main-sequence, which has a significant
influence on the age for these relatively massive giants. We identify six giant
members of NGC 6866 and derive asteroseismic measurements for five of them.
This constrains the convective-core overshoot and enables a more precise and
accurate age estimate than previously possible. Asteroseismology establishes
the helium-core burning evolutionary phase for the giants, which have a mean
mass of 2.8 . Their radii are significantly smaller than predicted
by current 1D stellar models unless the amount of convective-core overshoot on
the main sequence is reduced to in the
step-overshoot description. Our measurements also suggest that rotation has
affected the evolution of the stars in NGC 6866 in a way that is consistent
with 3D simulations but not with current 1D stellar models. The cluster age is
estimated to be 0.43 0.05 Gyr, significantly younger and more precise
than most previous estimates. We derive a precise cluster age while
constraining convective-core overshooting and effects of rotation in the
models. We uncover potential biases for automated age estimates of helium-core
burning stars.Comment: Accepted on 21/08/2023 for publication in Section 7. Stellar
structure and evolution of Astronomy & Astrophysics. 20 Pages, 11 Figures +
appendi
Simultaneous all-optical add and drop multiplexing of 40-Gbit/s OTDM signals using monolithically integrated Mach-Zehnder interferometer
A bit-rate flexible and power efficient all-optical demultiplexer realised by monolithically integrated Michelson interferometer
Deep phenotyping of the unselected COPSAC2010 birth cohort study
BACKGROUND: We hypothesize that perinatal exposures, in particular the human microbiome and maternal nutrition during pregnancy, interact with the genetic predisposition to cause an abnormal immune modulation in early life towards a trajectory to chronic inflammatory diseases such as asthma and others. OBJECTIVE: The aim of this study is to explore these interactions by conducting a longitudinal study in an unselected cohort of pregnant women and their offspring with emphasis on deep clinical phenotyping, exposure assessment, and biobanking. Exposure assessments focus on the human microbiome. Nutritional intervention during pregnancy in randomized controlled trials are included in the study to prevent disease and to be able to establish causal relationships. METHODS: Pregnant women from eastern Denmark were invited during 2008â2010 to a novel unselected âCOPSAC(2010)â cohort. The women visited the clinic during pregnancy weeks 24 and 36. Their children were followed at the clinic with deep phenotyping and collection of biological samples at nine regular visits until the age of 3 and at acute symptoms. Randomized controlled trials of highâdose vitamin D and fish oil supplements were conducted during pregnancy, and a trial of azithromycin for acute lung symptoms was conducted in the children with recurrent wheeze. RESULTS: Seven hundred and thirtyâeight mothers were recruited from week 24 of gestation, and 700 of their children were included in the birth cohort. The cohort has an overârepresentation of atopic parents. The participant satisfaction was high and the adherence equally high with 685 children (98%) attending the 1 year clinic visit and 667 children (95%) attending the 2 year clinic visit. CONCLUSIONS: The COPSAC(2010) birth cohort study provides longitudinal clinical followâup with highly specific endâpoints, exposure assessments, and biobanking. The cohort has a high adherence rate promising strong data to elucidate the interaction between genomics and the exposome in perinatal life leading to lifestyleârelated chronic inflammatory disorders such as asthma
Diabetic retinopathy as a potential marker of Parkinson's disease:a register-based cohort study
Neurodegeneration is an early event in the pathogenesis of diabetic retinopathy, and an association between diabetic retinopathy and Parkinsonâs disease has been proposed. In this nationwide register-based cohort study, we investigated the prevalence and incidence of Parkinsonâs disease among patients screened for diabetic retinopathy in a Danish population-based cohort. Cases (nâ=â173â568) above 50âyears of age with diabetes included in the Danish Registry of Diabetic Retinopathy between 2013 and 2018 were matched 1:5 by gender and birth year with a control population without diabetes (nâ=â843â781). At index date, the prevalence of Parkinsonâs disease was compared between cases and controls. To assess the longitudinal relationship between diabetic retinopathy and Parkinsonâs disease, a multivariable Cox proportional hazard model was estimated. The prevalence of Parkinsonâs disease was 0.28% and 0.44% among cases and controls, respectively. While diabetic retinopathy was not associated with present (adjusted odds ratio 0.93, 95% confidence interval 0.72â1.21) or incident Parkinsonâs disease (adjusted hazard ratio 0.77, 95% confidence interval 0.56â1.05), cases with diabetes were in general less likely to have or to develop Parkinsonâs disease compared to controls without diabetes (adjusted odds ratio 0.79, 95% confidence interval 0.71â0.87 and adjusted hazard ratio 0.88, 95% confidence interval 0.78â1.00). In a national cohort of more than 1 million persons, patients with diabetes were 21% and 12% were less likely to have prevalent and develop incident Parkinsonâs disease, respectively, compared to an age- and gender-matched control population without diabetes. We found no indication for diabetic retinopathy as an independent risk factor for incident Parkinsonâs disease
Cluster Ages to Reconstruct the Milky Way Assembly (CARMA): I. The final word on the origin of NGC 6388 and NGC 6441
We present CARMA, the Cluster Ages to Reconstruct the Milky Way Assembly project, the aim of which is to determine precise and accurate age measurements for the entire system of known Galactic globular clusters (GCs) and to use them to trace the most significant merger events experienced by the Milky Way. The strength of CARMA relies on the use of homogeneous photometry, theoretical isochrones, and statistical methods, which will enable us to define a systematic uncertainty-free chronological scale for the complete sample of Milky Way GCs. In this paper, we describe the CARMA framework in detail, and present a first application on a sample of six metal-rich GCs, with the aim being to unequivocally elucidate the debated origin of NGC 6388 and NGC 6441. Our results demonstrate that this pair of clusters is coeval with another four systems that have a clear in situ origin. Moreover, their location in the age- metallicity plane matches that occupied by in situ field stars. The accurate age comparison enabled by the CARMA methodology rules out the possibility that NGC 6388 and NGC 6441 were accreted as part of a past merger event
EFFECT OF SORGHUM SEED TREATMENT IN BURKINA FASO VARIES WITH BASELINE CROP PERFORMANCE AND GEOGRAPHICAL LOCATION
Sorghum [ Sorghum bicolor (L.) Moench] is a major subsistence crop
throughout the region of Sahel. With the exception of seeds and labour,
no agricultural inputs are in general used in sorghum production since
the grain is of a relatively low commercial value and the risk of
losing the crop to drought, flooding, etc. is substantial. A
meta-analysis of 118 field experiments was carried out to identify
conditions in which two protective seed treatments could support a
yield increase of sorghum in Burkina Faso. The two treatments were: i)
treatment with the pesticide Calthio C (thiram and chlorpyrifos) and
ii) treatment with an aqueous extract from the plant Eclipta alba .
Both treatments were found to produce a yield increase (Medians:
Calthio C +199 kg ha-1, P<2x10-9; E. alba +90.5 kg ha-1
P<4x10-4). A strong relative effect of Calthio C on yield (+36%) was
found for field experiments with a low baseline yield. A strong
relative effect of E. alba extract on yield (+22%) was found for
experiments with a low baseline of emergence. ANOVA of the 118 field
tests showed that baseline crop performance (yield and emergence) and
the effect of seed treatments were strongly linked to geographical
location (twelve different villages included). Roots from sorghum in
the village showing the strongest effect of both seed treatments
(>40% yield increase) were found to carry a comparatively high load
of the infectious ascomycetes: Fusarium equiseti , Macrophomina
phaseolina and Curvularia lunata .Le sorgho [ Sorghum bicolor (L.) Moench] est une culture de
subsistance de premi\ue8re importance dans toute la r\ue9gion du
Sahel. Exception faite des semences et de la main-d\u2019oeuvre, aucun
intrant agricole n\u2019est en g\ue9n\ue9ral utilis\ue9 dans la
production \ue9tant donn\ue9 que le grain a une valeur commerciale
relativement faible et le risque de perte de culture par la
s\ue8cheresse, les inondations, etc. est \ue9lev\ue9. Une
macro-analyse portant sur 118 essais au champ a \ue9t\ue9
effectu\ue9e pour d\ue9terminer les conditions selon lesquelles
deux traitements de protection de semences pourraient soutenir une
augmentation de rendement du sorgho au Burkina Faso. Les deux
traitements ont \ue9t\ue9: 1) saupoudrage de semences avec le
pesticide Calthio C (thirame et chlorpyrifos) et 2) trempage des
semences dans un extrait aqueux de la plante Eclipta alba . Les deux
traitements ont occasionn\ue9 un accroissement du rendement (valeurs
m\ue9dianes: Calthio C +199 kg ha-1, P<2x10-9; E. alba +90.5 kg
ha-1, P<4x10-4). Un effet relatif \ue9lev\ue9 du Calthio C sur
le rendement (+36%) a \ue9t\ue9 not\ue9 pour les champs
exp\ue9rimentaux ayant un rendement initial faible. Un effet relatif
\ue9lev\ue9 de l\u2019extrait de E. alba sur le rendement (+22%) a
\ue9t\ue9 not\ue9 pour les exp\ue9rimentations ayant une
\ue9mergence initiale faible. L\u2019analyse de variance des 118
tests a montr\ue9 que la performance de la culture (rendement et
\ue9mergence) et l\u2019effet du traitement des semences
\ue9taient fortement li\ue9s \ue0 la localisation
g\ue9ographique (12 villages diff\ue9rents impliqu\ue9s). Les
racines des plantes dans le village ayant montr\ue9 le plus fort
effet des deux traitements de semences (accroissement de rendement >
40%) portaient une charge relativement \ue9lev\ue9e
d\u2019Ascomyc\ue8tes infectieux : Fusarium equiseti , Macrophomina
phaseolina et Curvularia lunata
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