645 research outputs found
Fundamental parameters of massive stars in multiple systems: The cases of HD17505A and HD206267A
Many massive stars are part of binary or higher multiplicity systems. The
present work focusses on two higher multiplicity systems: HD17505A and
HD206267A. Determining the fundamental parameters of the components of the
inner binary of these systems is mandatory to quantify the impact of binary or
triple interactions on their evolution. We analysed high-resolution optical
spectra to determine new orbital solutions of the inner binary systems. After
subtracting the spectrum of the tertiary component, a spectral disentangling
code was applied to reconstruct the individual spectra of the primary and
secondary. We then analysed these spectra with the non-LTE model atmosphere
code CMFGEN to establish the stellar parameters and the CNO abundances of these
stars. The inner binaries of these systems have eccentric orbits with e ~ 0.13
despite their relatively short orbital periods of 8.6 and 3.7 days for
HD17505Aa and HD206267Aa, respectively. Slight modifications of the CNO
abundances are found in both components of each system. The components of
HD17505Aa are both well inside their Roche lobe, whilst the primary of
HD206267Aa nearly fills its Roche lobe around periastron passage. Whilst the
rotation of the primary of HD206267Aa is in pseudo-synchronization with the
orbital motion, the secondary displays a rotation rate that is higher. The CNO
abundances and properties of HD17505Aa can be explained by single star
evolutionary models accounting for the effects of rotation, suggesting that
this system has not yet experienced binary interaction. The properties of
HD206267Aa suggest that some intermittent binary interaction might have taken
place during periastron passages, but is apparently not operating anymore.Comment: Accepted for publication in A&
Development of high energy density primary batteries First quarterly report, 22 Jun. - 21 Oct. 1965
Electrode and electrolyte studies for lithium- copper fluoride batterie
Development of high energy density primary batteries 200 watt hours per pound total battery weight minimum Final report, 10 Jun. 1964 - 9 Jun. 1965
High energy density lithium-anode primary cells developed with energy-to-weight ratios over 200 watt hours per poun
Apsidal motion in the massive binary HD152218
Massive binary systems are important laboratories in which to probe the
properties of massive stars and stellar physics in general. In this context, we
analysed optical spectroscopy and photometry of the eccentric short-period
early-type binary HD 152218 in the young open cluster NGC 6231. We
reconstructed the spectra of the individual stars using a separating code. The
individual spectra were then compared with synthetic spectra obtained with the
CMFGEN model atmosphere code. We furthermore analysed the light curve of the
binary and used it to constrain the orbital inclination and to derive absolute
masses of 19.8 +/- 1.5 and 15.0 +/- 1.1 solar masses. Combining radial velocity
measurements from over 60 years, we show that the system displays apsidal
motion at a rate of (2.04^{+.23}_{-.24}) degree/year. Solving the
Clairaut-Radau equation, we used stellar evolution models, obtained with the
CLES code, to compute the internal structure constants and to evaluate the
theoretically predicted rate of apsidal motion as a function of stellar age and
primary mass. In this way, we determine an age of 5.8 +/- 0.6 Myr for HD
152218, which is towards the higher end of, but compatible with, the range of
ages of the massive star population of NGC 6231 as determined from isochrone
fitting.Comment: Accepted for publication in Astronomy & Astrophysic
Recommended from our members
The spatial relationship of human chromosomes within the nuclei of normal and emerin-mutant cells
Development of high energy density primary batteries Second quarterly report, 22 Sep. - 21 Dec. 1965
Copper fluoride-lithium high energy density battery developmen
Recent HIV prevalence trends among pregnant women and all women in sub-Saharan Africa: implications for HIV estimates
OBJECTIVES: National population-wide HIV prevalence and incidence trends in sub-Saharan Africa (SSA) are indirectly estimated using HIV prevalence measured among pregnant women attending antenatal clinics (ANC), among other data. We evaluated whether recent HIV prevalence trends among pregnant women are representative of general population trends. DESIGN: Serial population-based household surveys in 13 SSA countries. METHODS: We calculated HIV prevalence trends among all women aged 15–49 years and currently pregnant women between surveys conducted from 2003 to 2008 (period 1) and 2009 to 2012 (period 2). Log-binomial regression was used to test for a difference in prevalence trend between the two groups. Prevalence among pregnant women was age-standardized to represent the age distribution of all women. RESULTS: Pooling data for all countries, HIV prevalence declined among pregnant women from 6.5 [95% confidence interval (CI) 5.3–7.9%] to 5.3% (95% CI 4.2–6.6%) between periods 1 and 2, whereas it remained unchanged among all women at 8.4% (95% CI 8.0–8.9%) in period 1 and 8.3% (95% CI 7.9–8.8%) in period 2. Prevalence declined by 18% (95% CI −9–38%) more in pregnant women than nonpregnant women. Estimates were similar in Western, Eastern, and Southern regions of SSA; none were statistically significant (P > 0.05). HIV prevalence decreased significantly among women aged 15–24 years while increasing significantly among women 35–49 years, who represented 29% of women but only 15% of pregnant women. Age-standardization of prevalence in pregnant women did not reconcile the discrepant trends because at older ages prevalence was lower among pregnant women than nonpregnant women. CONCLUSION: As HIV prevalence in SSA has shifted toward older, less-fertile women, HIV prevalence among pregnant women has declined more rapidly than prevalence in women overall. Interpretation of ANC prevalence data to inform national HIV estimates should account for both age-specific fertility patterns and HIV-related sub-fertility
Linking concepts in the ecology and evolution of invasive plants: network analysis shows what has been most studied and identifies knowledge gaps
In recent decades, a growing number of studies have addressed connections between ecological and evolutionary concepts in biologic invasions. These connections may be crucial for understanding the processes underlying invaders’ success. However, the extent to which scientists have worked on the integration of the ecology and evolution of invasive plants is poorly documented, as few attempts have been made to evaluate these efforts in invasion biology research. Such analysis can facilitate recognize well-documented relationships and identify gaps in our knowledge. In this study, we used a network-based method for visualizing the connections between major aspects of ecology and evolution in the primary research literature. Using the family Poaceae as an example, we show that ecological concepts were more studied and better interconnected than were evolutionary concepts. Several possible connections were not documented at all, representing knowledge gaps between ecology and evolution of invaders. Among knowledge gaps, the concepts of plasticity, gene flow, epigenetics and human influence were particularly under-connected. We discuss five possible research avenues to better understand the relationships between ecology and evolution in the success of Poaceae, and of alien plants in general
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