1,238 research outputs found
The massive star binary fraction in young open clusters I. NGC 6231 revisited
We present the results of a long-term high-resolution spectroscopy campaign
on the O-type stars in NGC 6231. We revise the spectral classification and
multiplicity of these objects and we constrain the fundamental properties of
the O-star population. Almost three quarters of the O-type stars in the cluster
are members of a binary system. The minimum binary fraction is 0.63, with half
the O-type binaries having an orbital period of the order of a few days. The
eccentricities of all the short-period binaries are revised downward, and
henceforth match a normal period-eccentricity distribution. The mass-ratio
distribution shows a large preference for O+OB binaries, ruling out the
possibility that, in NGC 6231, the companion of an O-type star is randomly
drawn from a standard IMF. Obtained from a complete and homogeneous population
of O-type stars, our conclusions provide interesting observational constraints
to be confronted with the formation and early-evolution theories of O stars.Comment: 16 pages, 14 figures. Accepted by MNRA
The Struve-Sahade effect in the optical spectra of O-type binaries I. Main-sequence systems
We present a spectroscopic analysis of four massive binary systems that are
known or are good candidates to display the Struve-Sahade effect (defined as
the apparent strengthening of the secondary spectrum of the binary when the
star is approaching, and the corresponding weakening of the lines when it is
receding).
We use high resolution optical spectra to determine new orbital solutions and
spectral types of HD 165052, HD 100213, HD 159176 and DH Cep. As good knowledge
of the fundamental parameters of the considered systems is necessary to examine
the Struve-Sahade effect. We then study equivalent width variations in the
lines of both components of these binaries during their orbital cycle.
In the case of these four systems, variations appear in the equivalent widths
of some lines during the orbital cycle, but the definition given above can any
longer be valid, since it is now clear that the effect modifies the primary
spectrum as much as the secondary spectrum. Furthermore, the lines affected,
and the way in which they are affected, depend on the considered system. For at
least two of them (HD 100213 and HD 159176) these variations probably reflect
the ellipsoidal variable nature of the system.Comment: 12 pages, 20 figures, in press A&
The rotation rates of massive stars: the role of binary interaction through tides, mass transfer and mergers
Rotation is thought to be a major factor in the evolution of massive stars,
especially at low metallicity, with consequences for their chemical yields,
ionizing flux and final fate. Determining the natal rotation-rate distribution
of stars is of high priority given its importance as a constraint on theories
of massive star formation and as input for models of stellar populations in the
local Universe and at high redshift. Recently, it has become clear that the
majority of massive stars interact with a binary companion before they die. We
investigate how this affects the distribution of rotation rates.
For this purpose, we simulate a massive binary-star population typical for
our Galaxy assuming continuous star formation. We find that, because of binary
interaction, 20^+5_-10% of all massive main-sequence stars have projected
rotational velocities in excess of 200km/s. We evaluate the effect of uncertain
input distributions and physical processes and conclude that the main
uncertainties are the mass transfer efficiency and the possible effect of
magnetic braking, especially if magnetic fields are generated or amplified
during mass accretion and stellar mergers.
The fraction of rapid rotators we derive is similar to that observed. If
indeed mass transfer and mergers are the main cause for rapid rotation in
massive stars, little room remains for rapidly rotating stars that are born
single. This implies that spin down during star formation is even more
efficient than previously thought. In addition, this raises questions about the
interpretation of the surface abundances of rapidly rotating stars as evidence
for rotational mixing. Furthermore, our results allow for the possibility that
all early-type Be stars result from binary interactions and suggest that
evidence for rotation in explosions, such as long gamma-ray bursts, points to a
binary origin.Comment: 14 pages, 5 figures, accepted for publication in ApJ., no changes
with v1 apart from fixed typos/ref
Updating OWL2 ontologies using pruned rulesets
Evolution in Semantic Web content produces difference files (deltas) that track changes between RDF versions. These changes may represent ontology modifications and be expressed in OWL. The deltas can be used to reduce the storage and bandwidth overhead involved in disseminating ontology updates. Minimising the delta size can be achieved by reasoning over the underlying knowledge base. OWL 2 is a development of the OWL 1 standard that incorporates new features to aid application development. Among the sub languages of OWL 2, OWL 2 RL/RDF provides an enriched rule set that extends the semantic capability of the OWL environment. This additional semantic content can be exploited in change detection approaches that strive to minimise the alterations to be made when ontologies are updated. The presence of blank nodes (i.e. nodes that are neither a URI nor a literal) in RDF collections provides a further challenge to ontology change detection because of the practical problems they introduce when comparing data structures before and after update. In the light of OWL 2 RL/RDF, this paper examines the potential for reducing the delta size by pruning the application of unnecessary rules from the reasoning process and using an approach to delta generation that produces the smallest number of updates. It also assesses the impact of alternative approaches to handling blank nodes during the change detection process in ontology structures. The results indicate that pruning the rule set is a potentially expensive process but has the benefit of reducing the joins when carrying out the subsequent inferencing
Serum ferritin level and its association with gestational diabetes mellitus in pregnancy
Background: Short term as well as long term effects of GDM on both the mother and the child are preventable if screening and diagnosis are done at an early stage. Efforts have been made to try and identify clinical and biochemical markers that could predict GDM. Ferritin, an acute phase reactant is one such protein. This study was undertaken to know if there is an association between serum ferritin level and GDM in pregnancy.
Methods: A prospective study conducted in the Department of OBG, ESIC-MC-PGIMSR from January 2020 to June 2021. 388 gravid women satisfying the inclusion criteria were enrolled for the study after obtaining an informed written consent and maternal serum ferritin was assayed between 24 to 28 weeks of gestation and was statistically analysed.
Results: Both group demographic characters were matched and they were also matched for Hb% thereby eliminating anaemia, a confounding factor for the study. The mean serum ferritin level in GDM group was 46.4 ng/ml and in non-GDM group was 37.3 ng/ml (p<0.001). With ROC (Receiver operator characteristics curve) the cut off value of serum ferritin is 34.7 ng/ml with 95% CI, with sensitivity of 71% and specificity of 63%.
Conclusions: In this study S. ferritin value of >34.7 ng/ml at 24-28 weeks of gestation, there is 63% risk of developing GDM. Thus, we conclude that elevated serum ferritin level could be used as a biochemical marker for prediction of GDM
The Struve-Sahade effect in the optical spectra of O-type binaries I. Main-sequence systems
We present a spectroscopic analysis of four massive binary systems that are
known or are good candidates to display the Struve-Sahade effect (defined as
the apparent strengthening of the secondary spectrum of the binary when the
star is approaching, and the corresponding weakening of the lines when it is
receding).
We use high resolution optical spectra to determine new orbital solutions and
spectral types of HD 165052, HD 100213, HD 159176 and DH Cep. As good knowledge
of the fundamental parameters of the considered systems is necessary to examine
the Struve-Sahade effect. We then study equivalent width variations in the
lines of both components of these binaries during their orbital cycle.
In the case of these four systems, variations appear in the equivalent widths
of some lines during the orbital cycle, but the definition given above can any
longer be valid, since it is now clear that the effect modifies the primary
spectrum as much as the secondary spectrum. Furthermore, the lines affected,
and the way in which they are affected, depend on the considered system. For at
least two of them (HD 100213 and HD 159176) these variations probably reflect
the ellipsoidal variable nature of the system.Comment: 12 pages, 20 figures, in press A&
The mass of the very massive binary WR21a
We present multi-epoch spectroscopic observations of the massive binary
system WR21a, which include the January 2011 periastron passage. Our spectra
reveal multiple SB2 lines and facilitate an accurate determination of the orbit
and the spectral types of the components. We obtain minimum masses of
and for the two components of
WR21a. Using disentangled spectra of the individual components, we derive
spectral types of O3/WN5ha and O3Vz~((f*)) for the primary and secondary,
respectively. Using the spectral type of the secondary as an indication for its
mass, we estimate an orbital inclination of and
absolute masses of and , in
agreement with the luminosity of the system. The spectral types of the WR21a
components indicate that the stars are very young (12 Myr), similar to the
age of the nearby Westerlund 2 cluster. We use evolutionary tracks to determine
the mass-luminosity relation for the total system mass. We find that for a
distance of 8 kpc and an age of 1.5 Myr, the derived absolute masses are in
good agreement with those from evolutionary predictions.Comment: 7 pages, 4 figures; accepted for publication in MNRA
Pathways and Mechanism of Caffeine Binding to Human Adenosine A2A Receptor
Caffeine (CFF) is a common antagonist to the four subtypes of adenosine G-protein-coupled receptors (GPCRs), which are critical drug targets for treating heart failure, cancer, and neurological diseases. However, the pathways and mechanism of CFF binding to the target receptors remain unclear. In this study, we have performed all-atom-enhanced sampling simulations using a robust Gaussian-accelerated molecular dynamics (GaMD) method to elucidate the binding mechanism of CFF to human adenosine A2A receptor (A2AAR). Multiple 500–1,000 ns GaMD simulations captured both binding and dissociation of CFF in the A2AAR. The GaMD-predicted binding poses of CFF were highly consistent with the x-ray crystal conformations with a characteristic hydrogen bond formed between CFF and residue N6.55 in the receptor. In addition, a low-energy intermediate binding conformation was revealed for CFF at the receptor extracellular mouth between ECL2 and TM1. While the ligand-binding pathways of the A2AAR were found similar to those of other class A GPCRs identified from previous studies, the ECL2 with high sequence divergence serves as an attractive target site for designing allosteric modulators as selective drugs of the A2AAR
B fields in OB stars (BOB): low-resolution FORS2 spectropolarimetry of the first sample of 50 massive stars
Within the context of the collaboration "B fields in OB stars (BOB)", we used
the FORS2 low-resolution spectropolarimeter to search for a magnetic field in
50 massive stars, including two reference magnetic massive stars. Because of
the many controversies of magnetic field detections obtained with the FORS
instruments, we derived the magnetic field values with two completely
independent reduction and analysis pipelines. We compare and discuss the
results obtained from the two pipelines. We obtained a general good agreement,
indicating that most of the discrepancies on magnetic field detections reported
in the literature are caused by the interpretation of the significance of the
results (i.e., 3-4 sigma detections considered as genuine, or not), instead of
by significant differences in the derived magnetic field values. By combining
our results with past FORS1 measurements of HD46328, we improve the estimate of
the stellar rotation period, obtaining P = 2.17950+/-0.00009 days. For
HD125823, our FORS2 measurements do not fit the available magnetic field model,
based on magnetic field values obtained 30 years ago. We repeatedly detect a
magnetic field for the O9.7V star HD54879, the HD164492C massive binary, and
the He-rich star CPD -57 3509. We obtain a magnetic field detection rate of
6+/-4%, while by considering only the apparently slow rotators we derive a
detection rate of 8+/-5%, both comparable with what was previously reported by
other similar surveys. We are left with the intriguing result that, although
the large majority of magnetic massive stars is rotating slowly, our detection
rate is not a strong function of the stellar rotational velocity.Comment: 20 pages, 10 figures, 4 tables; accepted for publication on Astronomy
& Astrophysic
The properties of single WO stars
The enigmatic oxygen sequence Wolf-Rayet (WO) stars represent a very late
stage in massive star evolution, although their exact nature is still under
debate. The spectra of most of the WO stars have never been analysed through
detailed modelling with a non-local thermodynamic equilibrium expanding
atmosphere code. Here we present preliminary results of the first homogeneous
analysis of the (apparently) single WOs.Comment: 2 pages, 1 figure, Proceedings IAU Symposium No. 307, 2014, 'New
windows on massive stars: asteroseismology, interferometry, and
spectropolarimetry
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