1,639 research outputs found
Optical Interferometry of early-type stars with PAVO@CHARA. I. Fundamental stellar properties
We present interferometric observations of 7 main-sequence and 3 giant stars
with spectral types from B2 to F6 using the PAVO beam combiner at the CHARA
array. We have directly determined the angular diameters for these objects with
an average precision of 2.3%. We have also computed bolometric fluxes using
available photometry in the visible and infrared wavelengths, as well as
space-based ultraviolet spectroscopy. Combined with precise \textit{Hipparcos}
parallaxes, we have derived a set of fundamental stellar properties including
linear radius, luminosity and effective temperature. Fitting the latter to
computed isochrone models, we have inferred masses and ages of the stars. The
effective temperatures obtained are in good agreement (at a 3% level) with
nearly-independent temperature estimations from spectroscopy. They validate
recent sixth-order polynomial (B-V)- empirical relations
\citep{Boyajian2012a}, but suggest that a more conservative third-order
solution \citep{vanBelle2009} could adequately describe the
(V-K)- relation for main-sequence stars of spectral type A0 and
later. Finally, we have compared mass values obtained combining surface gravity
with inferred stellar radius (\textit{gravity mass}) and as a result of the
comparison of computed luminosity and temperature values with stellar
evolutionary models (\textit{isochrone mass}). The strong discrepancy between
isochrone and gravity mass obtained for one of the observed stars,
\,Lyr, suggests that determination of the stellar atmosphere parameters
should be revised.Comment: 13 pages, 9 figures, accepted for publication in MNRA
Arresting bubble coarsening: A two-bubble experiment to investigate grain growth in presence of surface elasticity
Many two-phase materials suffer from grain-growth due to the energy cost
which is associated with the interface that separates both phases. While our
understanding of the driving forces and the dynamics of grain growth in
different materials is well advanced by now, current research efforts address
the question of how this process may be slowed down, or, ideally, arrested. We
use a model system of two bubbles to explore how the presence of a finite
surface elasticity may interfere with the coarsening process and the final
grain size distribution. Combining experiments and modelling in the analysis of
the evolution of two bubbles, we show that clear relationships can be predicted
between the surface tension, the surface elasticity and the initial/final size
ratio of the bubbles. We rationalise these relationships by the introduction of
a modified Gibbs criterion. Besides their general interest, the present results
have direct implications for our understanding of foam stability
Resolving Vega and the inclination controversy with CHARA/MIRC
Optical and infrared interferometers definitively established that the
photometric standard Vega (alpha Lyrae) is a rapidly rotating star viewed
nearly pole-on. Recent independent spectroscopic analyses could not reconcile
the inferred inclination angle with the observed line profiles, preferring a
larger inclination. In order to resolve this controversy, we observed Vega
using the six-beam Michigan Infrared Combiner on the Center for High Angular
Resolution Astronomy Array. With our greater angular resolution and dense
(u,v)-coverage, we find Vega is rotating less rapidly and with a smaller
gravity darkening coefficient than previous interferometric results. Our models
are compatible with low photospheric macroturbulence and also consistent with
the possible rotational period of ~0.71 days recently reported based on
magnetic field observations. Our updated evolutionary analysis explicitly
incorporates rapid rotation, finding Vega to have a mass of 2.15+0.10_-0.15
Msun and an age 700-75+150 Myrs, substantially older than previous estimates
with errors dominated by lingering metallicity uncertainties
(Z=0.006+0.003-0.002).Comment: Accepted for publication in ApJ Letter
Modelling of the reef benthic habitat distribution within the Cabrera National Park (Western Mediterranean Sea)
Habitat spatial distribution is essential to know where to focus the protection of the seafloor resources. In this work, the bathymetry and backscatter seabed data show the importance of remote sensing applications and geospatial tools to have detailed information of the areas studied. The highresolution data enable to explore the environmental characteristics of selected Mediterranean habitats. These data were combined with available samples for ground truthing the habitat distribution model in the southeast of Cabrera National Park. The habitat modelling results show the high value of the studied area for ecological research. Unique communities of large filterers, including sponges, ascidians and bryozoans, were detected in this area. This study presents a potential habitat distribution map of the vulnerable reef habitat 1170, protected under the UE-Directive on the conservation of Habitats, Flora and Fauna, on the southeast margin of Cabrera Island.VersiĂłn del edito
Interferometric radii of bright Kepler stars with the CHARA Array: {\theta} Cygni and 16 Cygni A and B
We present the results of long-baseline optical interferometry observations
using the Precision Astronomical Visual Observations (PAVO) beam combiner at
the Center for High Angular Resolution Astronomy (CHARA) Array to measure the
angular sizes of three bright Kepler stars: {\theta} Cygni, and both components
of the binary system 16 Cygni. Supporting infrared observations were made with
the Michigan Infrared Combiner (MIRC) and Classic beam combiner, also at the
CHARA Array. We find limb-darkened angular diameters of 0.753+/-0.009 mas for
{\theta} Cyg, 0.539+/-0.007 mas for 16 Cyg A and 0.490+/-0.006 mas for 16 Cyg
B. The Kepler Mission has observed these stars with outstanding photometric
precision, revealing the presence of solar-like oscillations. Due to the
brightness of these stars the oscillations have exceptional signal-to-noise,
allowing for detailed study through asteroseismology, and are well constrained
by other observations. We have combined our interferometric diameters with
Hipparcos parallaxes, spectrophotometric bolometric fluxes and the
asteroseismic large frequency separation to measure linear radii ({\theta} Cyg:
1.48+/-0.02 Rsun, 16 Cyg A: 1.22+/-0.02 Rsun, 16 Cyg B: 1.12+/-0.02 Rsun),
effective temperatures ({\theta} Cyg: 6749+/-44 K, 16 Cyg A: 5839+/-42 K, 16
Cyg B: 5809+/-39 K), and masses ({\theta} Cyg: 1.37+/-0.04 Msun, 16 Cyg A:
1.07+/-0.05 Msun, 16 Cyg B: 1.05+/-0.04 Msun) for each star with very little
model dependence. The measurements presented here will provide strong
constraints for future stellar modelling efforts.Comment: 9 pages, 4 figures, and 5 tables, accepted for publication in Monthly
Notices of the Royal Astronomical Societ
Pancreas agenesis mutations disrupt a lead enhancer controlling a developmental enhancer cluster.
Sequence variants in cis-acting enhancers are important for polygenic disease, but their role in Mendelian disease is poorly understood. Redundancy between enhancers that regulate the same gene is thought to mitigate the pathogenic impact of enhancer mutations. Recent findings, however, have shown that loss-of-function mutations in a single enhancer near PTF1A cause pancreas agenesis and neonatal diabetes. Using mouse and human genetic models, we show that this enhancer activates an entire PTF1A enhancer cluster in early pancreatic multipotent progenitors. This leading role, therefore, precludes functional redundancy. We further demonstrate that transient expression of PTF1A in multipotent progenitors sets in motion an epigenetic cascade that is required for duct and endocrine differentiation. These findings shed insights into the genome regulatory mechanisms that drive pancreas differentiation. Furthermore, they reveal an enhancer that acts as a regulatory master key and is thus vulnerable to pathogenic loss-of-function mutations
Critical disorder effects in Josephson-coupled quasi-one-dimensional superconductors
Effects of non-magnetic randomness on the critical temperature T_c and
diamagnetism are studied in a class of quasi-one dimensional superconductors.
The energy of Josephson-coupling between wires is considered to be random,
which is typical for dirty organic superconductors. We show that this
randomness destroys phase coherence between the wires and T_c vanishes
discontinuously when the randomness reaches a critical value. The parallel and
transverse components of the penetration depth are found to diverge at
different critical temperatures T_c^{(1)} and T_c, which correspond to
pair-breaking and phase-coherence breaking. The interplay between disorder and
quantum phase fluctuations results in quantum critical behavior at T=0,
manifesting itself as a superconducting-normal metal phase transition of
first-order at a critical disorder strength.Comment: 4 pages, 2 figure
'It's a Form of Freedom': The experiences of people with disabilities within equestrian sport
This paper explores the embodied, gendered experiences of disabled horseâriders. Drawing on data from five inâdepth interviews with paradressage riders, the ways in which their involvement in elite disability sport impacts upon their sense of identity and confidence are explored, as well as the considerable health and social benefits that this involvement brings. Social models of disability are employed and the shortcomings of such models, when applied to disability sport, are highlighted. The data presented here demonstrates the necessity of seeing disability sport as an embodied experience and acknowledging the importance of impairment to the experiences of disabled athletes. Living within an impaired body is also a gendered experience and the implications of this when applied to elite disability sport are considered
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